PTTOIOCIIEMICAL CYCT,OIEHTDROæ}{ATTON

MACTIONSi"

A

THESXS

IAESffiNTED FOR TIfl DEffiEE OF

DOCTOR OF PIÍTLOSOHIT

Lrl

lTfE UNTITBR,SIÍT OF ADEI,ATDE

C.P. JOSTIUA

Deparbment of Organi.c Cheni.stry,

1967.

by

GTAPTER II.

II.1

TT..2

rf"t

CIIAPTER IIT a PTTOTOCHETtrSTRY

rlr.1

TI,I,"2

rllr5IIIo¿+

coNmNmi

nuB.oDUsxïo}i

A Review of Photoc̡emical Cyclo-d.ehyd.ro genation Re actions

Quantum ÏÍe1ds

Mechanistic Consid.erations for Photo-chernical" Cyclizat ions

Benzala¡iU¡¡e

Other Sr¡bstih¡ted. Schiff Ba,ses

ExperlmentaJ.

pHorocirErvrrsTRY 04 qE¡qzÀia¡[ILnE_ AND 0 _!B

ACID 3t+

t6

37

43

Paqe

(i)

(i")(")

CIIAPIER I.

r"l 1

T¿2

T..3

19

21

49

49

6t

65

ACETTT

Ami¡ro Azobenzenes

lyrAnino Azobenzene in the presence ofCarbor¡y1 compouncLs

Aoetyl, and. N1tro Azobenzencs

Ercperi.mental

59

CITAPIER, W.

nilo1

\I"2

ntrl o3

IV"4

ffil

tn 9V" Sulphuric acid

In benzene solutions

A comparative stud¡r of ratos ofcyclization

Ðcperinental

Er¡terinental

77

79

8¿r

89

96

106

115

122REFEREN@S:

PTJBIJIE'ATTONSI

(r)

S,Ul,{lvARY

lhe photoctremicai. reactions of benzalaniLine and- other sr.¡b-

stituted. Schiff bases ín 9t/, sulphuric acid. have been exanined. BenzaL-

anil-ine was found to und.ergo photochemical cyclodeLsrd.rogenation to

phenanthridi¡e and. simulta¡reous :red.uction to N-ber¡zy1anili:re" Substi-

tuted. Schiff bases, howeverr-dü nob r:r¡d.ergo $rotochemicaL cyelízatíon;

and possible causes of the pleotochemical stability of these compound.s

are d.iscussed.o

The photochemical reactions of amino-, nj-tro-, anct acet¡rI-

azobenzenes in !tr/ó sulphuric acid. have been stud.ied.o þAmi.no ard. 4r4.t-

d'ia¡rinoazobenzenes were not cyc];ízed, but their benzílid.ene d.erivatives

were shoun to und.ergo ¡ùiotochemical cyclod.ehyd.rogenation to give 2-amino-

and, 2 r)-dia¡ninobenzo lg] cinnoline respectively. J-Lmínoazobenze ne ard.

J-benzalamin oazs6.^r.ne both gav e J-aminobenzo þ] ciruroli-ne. 4-Nit ro-

and. þace tyl-azobe rLzerLe gav e 2-rit ro. and. 2-acetïLben zo þ]cinnofi-nerespectively, and. J-nitrn- and J-¿sstylazobenzene yielded. J-ni¡ro- anfl

5-acetylbenzop]cinnoline. The effects of substituents (eleotronis

i¡¡fl"uences and. positions of substitution) on the photochemical cyclo-

d.e\rd.rogenation reaction of a.zobenzene are discussed in tlre light of a

mechanism postulated. by Bad.ger, D:reler and llewiso

A stufrr of the photochemical- prcperties of azobenzene-Z-

carboxylic acid. and. its [-chloro-, 4'-chlo¡p-, l¡-methyl- and. l+r-metJ:yl

d,eriva.tives has been mad-eo A1I these compound.s were photochemically

cyclodetgrd.rogenated, ir: 9g/" sulphuric acid. to the reJ-ated benzoþlcinnolj-ne-

þcarborylic acidso In the cases of azobenzene-?-cùrboxylic acid. ar¡d.

I ar/

its l¡r-methyl d.erivative ejection of the carboxyl group occu¡red to a

small extent. Attempts to prepare tlie cis-i.someris of the varior¡s azo-

benzene-Z-carbo4ylic acids (for photo kinetic studies) by irrad.iation

in benzene solutions were unsuccessful, but photochemicaf d.ecarboxylation

was for:nd. to occur. Azobenzene-2-carboxllic acid. and. its 4r-methyl-r

,Lr -chlora-, and. 4t -d.imethylamino- d.erivatives wer3 thus par:biaIly

d-ecarbo4yl,ated. on j-rrad.i.ation j¡r benzene solutionso Extension of t'Lrjs

reaction to anthra¡rilic acid. and. its benzal d,erivative shorveð that partial.

d.ecarbo4ylation takes place in these cases a-Lsoo Azobenzene-J-carboryIic

acid. and. azobenzens-þcarbo4ylic acid. were stable und,er these conditionso

The possible i¡tervention of a zwitterion:ic form j¡r the photochemical

d.ecarboxylation is d.iscussed. The infrared. absorption of the neutral

corrpowrd.s have prrovid.ed confirrnation for intramolecular hydrngen bond.ingt

ancl the photochemical properties of azobenzene-z-càrboxylic acids in

relati.on to this phenomenon is d.iscussedo A comparative stu{¡r of the

rate of cycLizatíon of azobenzere-2-carboxylic acid. has been wd.ertaken

a¡rd the rates of eycLízation was found. to dec¡ease j¡r the orcler¡ Ãzo-

benzene-2-carbo{yfic acj'd ) lrchloro d.erivative ) l+t -chlon¡ aerivativ}

þmethyl d.erivative) [r-met]¡rl d.erivativeo An attempt has been made

to rationalize the effect of substituents on the rate of cyclization.

The photochernlstry of 2 r2r -azod.iphenylmethane has been exam-

ined. since this compound. was of r.e]-ated intertest to metkgrlazo]oenzerÊs.

No reaction was evid,ent on its i¡rad.iation in neutral" solver¡tsc However

in 1% ethanolic sulphuric acid, a photo-ind.uced. reaction took place and.

d.ibenzo Fdl fl ,2] alazapin-11-one , 2 ,2'-d.iaminobenzophenone, ar:d. two other

(iii)

prod.ucts (probably 2 r2r -díarnínod.ipher¡rLnethane arÊ, 2 r2r -ltydrazobenzo-

phenone) were fo:cnedo The last trrro pnod.ucts were not fully charact'etizeð.o

Irrad.j.ation of 2 r2r -azodiphergr}nethane in 9V" sulphuric acid. fo¡med. on\r

one prod.uct; a sulphonic acid. of composition Ctfl,*NZO5S, pmbablg 2¡2'-

d.ianrinobenaophenone-5-sulphoniþ' acid.. On irrad.iation of &ibenzoprg]-

Fre]-¿i"zap)n-11-one ín 1/å ethanolic sulphuric acid. the onþ prcduct

formed. yt¿s 2r21.-d.iamjnobenzophenoneo A pnobable mechanism for ttre photo

¡¡eaction in etkranolic sr.ùphurio acid. is d.iscussedo

**t*

( i")

STATEI\E}TT'

fhis thesis contains no material previous\r submj.tted

for a degree or d.iploma in aly Universityr and. to the best

of my knowledge and. belief, contains no material previousþ

published, or written by another person, except v¡hene due

refererce is mad.e in the texto

(")

A C IC'lOr¡r¡LE D ÉÎvE lf IS-

I welcome tÌús opportr:nity to exp:ress 4y sJlcere thanks

to Dr. G.E. Lewis and. Professor G.M. Badger for their guidance and,

encouragement during the course of these investigationso

G¡ratefr:l acknowled.gement is mad.e to the Petroletxn Research

Fwrd. administered. by the American Chemical Society for the suppoz'b of

this work"

Ad.d.itional financial supporb was received. from lhe University

of Ad.el¿¡:iae (1965-1967) and. CIBA of Ind.ia Ltd.. ?geù. Gratef\¡l acknow-

led.gement is mad.e for this support.

I Ìy:ish to express qy apprcoiatÍon to Dro R.B. Johns, The

University of Melbourne for provid.ing a reference sample of dibenzo-

tS$ 0 rZ)aiu"upin-11-one, to Dro J"H. Bowie for d.eternrining severa.l mass

spectra ar¡d. to Dro Î.Mo Spotswood. for the rrrrtrorc spectrum"

***

CHAPM:R I

ITIIRODUCITON.

I o

I.1 Ä Revierv of Photochernlcal C¡¡clo-dehyd¡pfrenation Reactions

lhe earliest obse¡vation of a photochernical- cyclod.ekSrckagena-

tion reaation uas by Stobbel in t9O7 r¡ihen l-phergrlnaphthalene-2r3-

d.icarboxyii-c arù1yd.riae (Z) was isolated. from tlre ilrad.iated. solution of

d.ibenzalsuccj-nj-c arrkryariae (1) in chLoroforrn or benzene containing traces

of iod.ine. But it was not r¡ntil 1950 anottrer such photo-induced. reactÍon

_>

6H5

(r) (z)

2was reporbed.¿ when phenanthrene (4) was isolated. from an irrad.iated

solution of stilbene (J). Ear1j.er, Smaln:1"5 t rd. Lewis4 had. observed

tlre fo¡rnation of a nelv compound. shorvi4gÀr-, 2+7 ryt during their stud'ies

on photoctrenrica-lly irrd.uced. gq-!¡gnå isomerization of stilbene solutions

but they <Ìld. not attempt to isolate and. characterize the compoundo ItÂ

was Buclcles' vÈro later isolated. and' id'entified' the compound' as phenart-

threneo

In recent years 1ùotochemical cyclod.ehyd.rogenation reactions

have receíved consid.erable attention and severa-t publications have

appeared. on tkre photockrenica-t cycli zation of stilbene d.erivatirr.t6-18

a¡rd its analogues .19-22 nipherylanine a¡¡d. its N-substituted. d.eriva-

2.

ß) (+)

tiv"t23,24 a¡:ð. azobenzene and. its d.erivu.tiv.s26-32 h^u" also been photo-

chemica$r cyclod.et¡rd.rcgenated. lhe successfi:-l photo-induoed. cyclization

of a few Schiff ba.ses a:¡e likewise on recoñ.33-t6 Althougþ varior¡s

other photochemical cyctizations of conjugated. dienes (5), trienes (6),

ard. relateô oompound.s are ls:,ornn9t59 thi" review wiJ.l be li-mited' to the

rllscussion of ¡ùoto-cata\rsed. cyclod.ek¡rd.rogenation reactior¡s of stiLbene

'd,ipher¡ylamíræ, benzalar¡iline, and. azobenzene and. their derir¡atives.

(¡)

3

-->(6)

rS ion of stiLbene and its d.erivatives.

Ihe photo-in¿uced. cyeLízatíon of stilbene to phenanthrene

has been extend.ed. to stilbene d.erivatives with sr¡ccess for the prepara-

tion of mar¡y sgbstituted. phena-nth:rerru"o15 Thus the photoæornrersion of

stilbene bearing bromo, chloro, carboxy, fluoro , ræthyL, methorrry, pher¡fI,

and. trifluoromethyl substituent to the related' phenanthrenes has been

achieved. ,.9-r -prr -and. ClFsubstituted. stilbenes affordeè 1-2 3-t ard' 9-

sr¡bstituted. p):enanthr€nes respectiveþ and. m-substituted. stil-bene yield'ed'

a nixtuæ of 4- ard. 2-substi,tuted. phenanthrenes. No cyclization Ï¡as

obse¡ved.15 nh"r, an acetyl-, d.i-methylamino-r nitro-, i.od.o-, or a¡Lino-

substituent was present in the stj-Ibene' However, i¡rÀren iracetyl-stilbenet

þacety¡-stilbene an5l, and. þpher¡rlazostilbene were irrad.iated. in strongJy

aciðic solutions spectral changes characteristic of cycLízation were ob-

""*"d..J7 rhe presence of an oxj-d.ant was necessarylo ir, "^.h case for

the cycliza1,::orL to occur. In atl the above experinents iod.ine was present

or. the irrad,iatcd. solutions wsre exposed. to air. Relnrts to the con-

7 a -10ttaryl rY have been elq)la1¡.¡ed on the basi-s of olrygen or some other

oxid.ant bej-ng inadvertent\r present. lÀkren Grdr-d'icyano stilbere (7r

R s Rt , CN) rivas i.¡zad.i.ateô in the presence of o:qygen or iod'ir¡e 9 r1O-

4

dicyanophenanthrene (9r R = Rr= Cl{) was fo:med. in good. yiefalg lhen

the presence of a¡ oxidant was carefulLy exclud.ed a¡r alnost quantitative

yie3-d. of trans-g,10- dÍhydro-9, 1o-d.icyanophenaathrene (8, R = R, = cI{)

rras obtalo"d.l8 Similar results were obtained. vlren d.iphenyJ.naLeic

anhydride (7, RrR = c0.0.c0) a¡d d.iphenyrnaleimid,e (2, R,R'= c0.NE.cO)

were irracl'iatecl. l?hen stilbene was j.nadiated in carefu].ly d.egassed,

hv_> 0c

ER

ft) (e) (e)

solutions only gis-Jrarxs. fsomerization took place wj-th virtuarly no lossof stilbenel4

letraphenyl eth¡¡lene (lo) has been photoconverted to 9110-

ciipheqylphenanthren" (1t) Uut a second ring closure to (lZ) f¡as not been

( to¡ (tz¡

-+

(tt¡

Ã

1)+aohleved, even on prolonged. irrad.iation"

The failure of o-terpher¡yI (ç) to q¡rc\l-;ze photochemi""uyl4

to tripher¡yLene (14) Ied. Mallory and coworkers to postul ^t.14 that the

necessary conòition for cyclization was that the centra-l d.ouble bond.

shor:ld. be olefi:uic i¡ character, but thj.s assumptioll Ìvas found. to be

incorrect when it was later found. thatc-terphenyl (15) cycf lruuð'17 to

terpher¡rlene (tL) on being irrad.iated. in solutior¡s j.n the presence of

iod.ine,

--

(r¡) ( 1L)

lhe ¡nost satisfactory oond.itions forud. for the preparative-

scale photo-cornrersion of stilbenes irnrolve the use of a combination of

oxid.ants, o)$rgen and. j-od.ine, in cyclohexane so]r.tionsol+ Sulphur,

telluriurn, seleniurn ðioxid.e and. palla*ium on carbon we¡æ not satisfao-

tory as orid.ants. Chloranil and. selenir¡n were effective but these had.

experjmental tisadv*tug"".1+ the presence of copper h4lid'es was f'ound.

to i-rnprove the yield. in oertai n cycLízabio*.,8

6.

Cyclization of s¡UÞc4q analoques.

Load.er, sargent and. Ti¡mon"19 ",r"."ssfurly prepared. azap¡¡ena¡

threnes follovring the irzad.iation of 2-t 2-t and þstyryI pyridines.

This was contrary to previous report=14115 that stilbazoles resistphotocyclization. Thr:s benzop]isoeuinoline (t6) was isolated. in good.

yield following imadiation of J-styrylpyridine ('ts) " Further work þBortolus and. cov¡orku""2O cor¡fi::ned. the find.ings of Load.er.-g! d, rhey

a-lso duccessfully cycLízed. j-, l+-r 5-, and. 6-methyl sr:bstituted. 2-styryI-pyrid.ines to the æIated. azaphenanth¡enes; wittr tl:.e ejection of the raetþ1gnoup ín the case of J-netþI 2-styry1pyridi.¡re.

-->

(tÐ (16)

Perkamlrus and. Senger2l stud.ied. the quantum yield. for the d.isap-

pearance of several 1r2-dipyrid¡rlethylenes when these r¡rcre i¡raùiated.in solution a¡rd they attributed. the fina.l slrectnur to the corresponding

¡henanthrolenas, althougþ noræ of these we¡e isolated. a¡,¡d. l-d.entified..

thiophene analogues of stilbene have al-so been ¡hotocornr et1,eda?

ir¡to the reIated. cyclized. productso Thus, follovring the i¡rad.iation of

7.

solutions of 2-styrylthiophene (t7, n = n) and. i-ts methyl d.erirratives

in the presence of j-od.ir¡e, near quantitative yields of tåe correspond.ing

naphtho [Zr1-Ðthiophenes (ta) uere obtainedo Sirnilarly 11-thiabenzo-

þ]fluorene (ZO, R = H) v¡as obtained from J-styryI benzo[Þ]thiophene

(t9, n = H).

B' B

(tt) ( re)

(tg) ( zo)

ïlhen Jt-nett\y1-2-sty¡y1 tLriophene (17, n = lr-Me) viras irrad.iated., both

possible j-someric prod.ucts være fo¡rned. and. in the case of 2r -alethyl.

d.erivative (17rR = 2'-Me) a parbial ejection of the metì:ry} group also

was obse:¡redo Si¡rilar results were obtaj¡red. witb Jr -¡netttyl J-styryl

benzo[b]thiophene (t9, n = J'-Me) and. 2t -met]¡yl J-styryl benzo[lJthiopher:e

(t9, n 'n 2r-Me)o

8n

Phntonw¿':'l å-q]-.inn nf zlin and. its d.erirmti-ves

During the iryad.iation of d.iphenylamine and. its N-methyl and.

N-plrer¡yl d.erivatives (Zl) in sotutions Grellman and. coworkarszS obseied.

the formation of the appropri-ate carbazole, (ZÐ" N-Methyl and. irt-pher¡rI

d.ipherylamines fo¡med. corespond.ing N-netliyl-, and. N-pheryl-carbazoles

i-n about 70 arÊ, 65/" yíeLd. Ihe yi.eId. of car}azole from d.iphergrlaar:ine

lvas poor due to sid.e reactions. An j.on:lc mechalism has been p*po""d.25

i¡¡ which the intermed.iate þ-, j¡b-d.i}yd.rocarbazote (ZZ) :regard,ed. as arisi.¡¡g

from the excited. ionic species is converted. to carl>azoLe by oiçygen or

at least 5n part by elimination of molecular Ì5rd.rogen.21+'25

H

hv_>

(zt) n = H, Me or Ph (zz)

Photo-corwersion of Schiff bases

Oc

(4)

the neptacement of a CH= group in the ethylenic linkage of

stilbene with a nj.trogen atom gives a Schiff base.' Attempts mad'e by

several *ork"""7'14 ao photocyclize Sohjff bases rr¡ere unsuccessful and.

I{a11ory and. cowo"k"""1b were led. to suggest that it was due to the rapid'

therr¡raI Slg-jgg¡å isonerization of gcllj.ff bu."u".@-4J llrcreover due to

ct

their instability prolonged. irradiation destroys Schiff bases conpletely.

Recently Cava a¡¡d Schlessin ger73 for.¡nd, that 1-naphtbal-1 '-naphthylamine

(24) ror¡oed. dibenzoLg'Ð phene.:nthridine (25) -

---4

(24) (25)

Mallory et aI. reexa.mine¿,4 ttr"i" earlier workrl4 or, .this

report, and confÍrmed their previous find'ings that at room ternperature

no cyclization occurred. However at low tenperatures (1Oo) they were

able to detect snall qua.utities of the cyclized prod'uct (27) ¡ut pro-

Ionged irradiation again d.estroyed benzalar¡iline (26,R =H).

->

(zø) Q7)The stereochemicaf interpretation for the lack of photo-

R

10.

cyclization of benzala¡iline at roorn temperature has boen substantiated

by two experinents. Firstly by írradiating solutions of benzalanil-ine

at 10oC in order to reduce thermat -crs-lrans. rate and hence Íncrease the

photostationary concentration of the gþ-isonor, tbey were able to d.etect

up to *¡4" conversion to phenanthridine.

Second.ly N-d.iphenyhoethyleneaniLine (26, R = C6E5) a conpound'

whose photocyclization is not subject .to the stereochemicaL iubÍbttion

nentj.oned. above, was found to be converted pbotochenical-Iy to 6-pbenyl-

phenanthridine (27, n = C6U5). Àgain the photoreaction did not occur in

the absence of a¡ oxida¡rt.

g-DÍraethyla.minobenzylid.ineanil"ine (eg) afso has been ""po=ted't5

to fo::n 9-d.inethyla.minophena¡thridine (29) ín about 1f/o wlrøn irradiated

in etha¡o1ic solution. fn add.ition azobenzene (7fl") a¡d 4,4r-bis(dinethyl-

anino)stllbene (Zy/") were isolated. These appeared to have been fortoed

"z

(zg)(28)

by a sid.e reaction, presnably through the inte::mediacy of a substituteti

diazetid.ine.

11.

Products of an unerpected. type were encountered by sbanaon

and. cowork.rrT6 during tbe course of sorne photochenicaL investigations

of ring closure reactíon in Sciff bases. Ilhen benzal-2-naphthyJ-a:cine

(rO, n + H) was Írradiated. in ethe¿roI erposed. to aÍr 2-pihenyl-5¡6-

benzoquir^oli¿e (rt, n = E) was forned. with the Íncorporation of a C,

fragment fron the soLvent., À sinilar reactioÍr was observed when 4t-nothory

benzal-2-naphthylanine (rO, R = O-Me) was irradiated in ethanolic solution.

$o¡ (t1)

Photochenical-. Reactions of Azobenzene and its d.erivatives.

The cis#trans equilibretion of azobenzene on Írrad.lation in

neutral soLutions or in acetic acid. has been l¡eown for a tons tinel4

Although benzo g cirurollne was obtaÍned.45'46 'þy tbemal cycl"ization of

azobenzene in alunÍniur¡ chloride ne1ts, it was not until recently that

such a reaction was shoÌrn to occur pbotochenically'

l,e*is26 in 1960 isorated benzo[e]cinnorine (¡¡) rorrowing

prolonged. irrad.iation of strongly acid,ic solutions of azobenzene (32),

4oaLa

a reaction approximately 100 tj¡nes slower than that of the -gjg:!¡3!åequilibration, A si¡lilar reaction was observed. i-:rd.epend.ently and.

-,si¡nrrltaneousþ by Hugelschofer, Kalvod.a, and, Schaffnerr when acetic

acid. solution of azobenzene ï/as irrad.iated in the p¡esence of ferric

chloride.

ßz¡ 0s)

In 2{ sulphuric acid. azobenzerLe exists almost enti-rely in

the pnotonated. form and. it has been shown2T tn^t the cycti- zati.:on is pre-

ced.ed. by rapl-d. trans<=+ cis equilibration of the catioto (¡+ -l¡¡).

+

(¡t*) 3t)

In later e:çerim"r,.t"47 it has been found. that benzíd.ine was fo¡sred.

approxinately in the sa.me yie1d. as benzofclcir¡r¡oline. In view of thj-s

13"

fact it is assr:riea28 tfr".t in 22N sulphuric acid. the cyc)s-zatíon is a

photoc)remical d.isproportionati;. Protonate d. azobenzene has been re-

pott"a48 to be a po'rverful abstractor of hyd.ride ions a¡rd. it is reasonable

to conclud.e that the hyd.rogen eliminated. in the cyclization process re-2¿l

d,uced/ a second. molecule of azdoenzene to hydrazobenzene (¡6) wfricfr

rearranged. r:nd.er the acid. cond.itions used., to give benzid.ine (lù.

Gc) 3t)

Following the initial success with azobenzene, photocate-r-ysed.

cyclízatíon of severaL azobenzenes sr:lcstituted. with chlo4s-, carboxy-¡

iod.o-r methylT and. phergrl- groups has been investigaæaãU3} in 22$

sulphunic acid.. JpSu.bstituted. azobenzenes formed. 2-substituted. benzo-

l-c'lcínnolines. J-Sr:bstituted. azobenzenes as expected., fonneô a nrixtr:re

of both the possible I-t and. J-substituted. benzo[c'lcinriolines, the

proporbion of the J-ess stericalþ hind.er.ed. J-substituted one pred.omina-

ting over the other, From 2-substituted. azobenzenes [-substituted.

berøol"c''lcinnolines were obtained. with tkre accompaniment of small quanti-L-¡¡

ties of the parent Uenzo[g] ciruroline formed. by the ejection of tk¡e 2-

substituent. $'imif¿¡ ejection of the 2-substj.tuent was also obse¡ved.

in the case of 2-methoxystilbenerl5,'-methyJ,-2-styrylthioplrerru22r ad

J-ic,e tL¡r1-2-s tyryIpy"iùirr". 20

1 l¡'.

lfhen 2r2¡r6-trjrnettrylazobenzene (58) was inad.iated. in acid.

soru'r,ion the e>1oected. 2r4-dirnethylbenzo[g]cinnoline (rg) u*" formed..by

the ejection of a methyl grou;o from the 2-position. In ad.d.ition a sma|L

amou¡.t of l r2lytrimethylbenzo[g]cinnoline (æ) *a" :arso isolated.o The

latter was fomed. due presumably to a migration of the ræthyl group in

the 2-pos ítLon"Z9

MeMe

Me Me Me

(¡e) (+o¡Gg)

trn all the 1ùrotochemical cycU-zation reactions of azobenzenes

the erpected. benzid.ine rearrangement prod.ucts were also j-soIated. except

i¡ the case of 4-netlgrl-r md 2r\r6-itimethyl azobenzeneso Abnorma-l

rearrangement prod.ucts were fo::ned, i.n these caseso28o29

P¡eriminary quatitative experiments showe¿49 that strongry

conjugating substituents in the J¡-position irùribit cyclod.ehyd.rogenation

reactior¡s and. no qycLization cor¡ld" be d.etected. when l+-anrino-r49

þd.irnethyl"*irro-r49 and. þphenylanr:ino-17^tob"*enes wer¡e irrad.iated. in22I sulphurj-c acid.o

. The photockrenrical reactivities of a few azonaphtlnalenes and.

4^

phenylazonaphthalenes have been e>taminedSo l"t"lyo 1r1t-, tr rzt-, anð' 2r2t'

Azonaphthalenes rt¿ 2-phe4y¡! azorøphthalene were not photocyclizecl und'er

the cond.itions i¡r wk¡-ich azobenzene was converted. to benzofgci-nnoLir^e"

However 1-phenylazonaphthalene (41) cyclized' to give naphtho fûrz-ij -

ciruroline (+Z¡.

(+t ¡ (+z¡

More recently photochem:icaI reactions of azobenzeres have

been extend.ed. to l¡-styryla zobenzene and' two conjugate a32 and two non-

corr.jugateå bisaro "o*po*rd.""J7

Altkrougþ dilute solutj-ons of ,l¡-styryJ-a.7s-

benzene on irrad.iation showed strrectral changes clraractpristic of cycLíza'

tion to a benzofs]cinnoline d.erivative, the q¡rclízed prod.uct could. not be

isolateô.Jo

lbe bisazo compou'.ids on irrad-iation in 9% sv¡phuric acid.

u¿""" "ho1,^Jz

to cy"Iize around. one azo ljnkage, accompanied. by reduction

a¡rd. rearra¡gement at the other group. Ihus þpherryrLazoazoUenzene (À-J)

on photocyclization aff ozrd.ed 2-ewmct-1-(4-arÈnophenyl) benzo[gl cinnoline

(¿+) an¿ Z-(¿r-am:lnophenyl)anÍnobenzofc-l cinnoline (+¡). Some n-,inor

16.

Gs) (r+) Gs)

d.ecomposition prod.ucts accompanj.ed. the prod.ucts. No d.oubly cycJ-ized

compowrds røere fo¡med.o

4rl+r -bis(pher¡ylazo)lipfreryf also underwent a sj-milar cyeLíza-

tion ¡eaction affordjng 2-(t'-a¡ninoIùrer¡y1)benzo[glcir,:eoline arrd. 2- 4'-

a¡uj¡o.Jt-(4,-^r¿tropher:y1)pherqyl benzolcJ cinrroline. Both non-conjugated.

4¡4t-bis(phenylazo)bipher¡yr methane (¿*6, n = "úIr.) aria 4r)+r-bis(pher¡r1-

azo)blben?,Vl (\6, R = .úId{,t12.) also cyclized arsund. one aza linkage

ard concoi¡r:itantþ urderwent red.uction and. rearrar¡gement at the otlv¿c azo

grþupo thus 4r4r-bis(phenytazo)uipnerlylmethane (¿6r fl c .CH2o) on photo-

oycliøation gave 2- l+t -araino-J | - ( t¡' -arninophor¡¡I) benøyl benøo [s.] cinnoline

(+7, R = .CEI2.)

2

IJ

17"

H2

(¿rß) (t.l)

lhe photocata$rzed. cycTiza'aion of 2-pherylazobenzol*cinno-

rine (+8) ín 9% sr:lphurio acíd has been "ho*J2 to give a pentacyclio

prod.uct probabþ a benzo V r2-rl+r5-Sl dicl¡rioline (49) along with two

decompositi.on proèucts (U+) and (45).

(4s) (+g)

18.

Although þCi:rrethylam:lnoazobenzene cou1d. not be photocyclized

to the benzofclciirnoline d.erivative, more recent work in this Labotatoryt- I

"Ir.ow"d5o tJrat N-oxid,e of the 4'-d.imethylaminoazob enzene (50) can ¡e

photochemically cyclod.ehydrogenated. to the related. benzofJ einnoJ-lne (51).

e },rlúe2

-)

0 2

(ro¡ (¡t )

An i¡rteresting photochenr-ical reaction of azobenzene v'ras

obsezvede'1'52 when it was irrad.iated. i-n acetyl chLorideo NrN¡-

d.iacetyl-þchlorohydyazúenzene (52) vuas fornred i¡r high yield. In th-is

case concomitant substitution in one æglg position and. reductive d'i-

acetyLatíon at tlne azo linkage occur.

cl_

$z¡

hYry$z¡

^ü

cH-)

19"

TT.2 Quantum Yields"

The quantwr yielcls for the cycl-:Lzat.Lon of stilbene, dipher¡¡l-

arnine, Schifft s base a¡rd. azobeflza\e have been d.eterrninedo On1y broad.

cornparisor/s are trnssible, horvever, because of d.iffe¡ent corditions used.'

Stilbenes when irrad.ia'ced in cyclohexane solution (/+ * 10þ

at J1J mF in the presence of oxygene to form phenanthrene, shorveerl? o

quantum yield of þ o.oz. When lolver concentratio.,. (td5y) of gþ and.

tranq stilbene were irracliated. in hexane thre quantu* yi"fau were much

higþer.B the quantum yietd. for.the eycLlzation of triphenyl etL¡r1ene

to r&i;låH$#"ff,i" d,etermined. by Mart ory et ù.3'* and. values of / o.o5

ancl over være obtained.o

. the quanturn yield.s for the cyclizations of d.ipherylamines to

carbazol-es were sholrrn to òiffer at ùifferent o¡ygen concei'itrations. In

hexane at rpom tempera.ture, in thre presence of o4ygetl, the quantun yie1d.

of carbazole prod.uction trr.sses througþ a naxi¡num.%tþ Thus for ùiphenyl-

amine þ ^* was câcO.O8 at [Oj mær z x 1O+'y. In air saturated

hexane LOã= 3 x lü3y þ *u, much Less (ca.O.O2)" O4ygen inLribj-tion

was found.Z4 to be more apparent for d-iphergrlarnine than the other N-

subs tituted. diphe rrylaraines o

Itre quantum yie1d. for the photocyclizatLon of N-C.iphenylmethylene-

an:L1ine to 6-phenylphenarrthrid.j:re v,ras d.etemined.. 5 x 1O-lg Cyclohexaae

solutior¡s were irrad.iated. at J'lJ my,. The values lrere fou¡¿Jh to be of

the ord.er of (ø 1 x 1O{) extremely lovr i¡r comparison to that of tripher¡yl

etl¡rlene (Ø S * 1O-2) wrder the same cond.itions.

ô^LVa

lhe quantum yield.s for the photochemical cyclízal.íon of azo-

benzene in vario's normalities of sulphuric acid. vrith +36 nY and. l4ol n*

rad.iation have al-so been stuùied.oJ1 A *a"ked- d'ecrease in quantum yieLd'

(þ O.OID5 to þ O.O11f+) w-ith increase in acidj-ty of the rreaction has been

observed.o There were only relativel,y small changes when temperatrre lqas

Iov,¡ered. or when the wavelength of racLi¿tion was changed. the quanturi

yield.s for the cyc!ízatíon of azoioenzene ta benz.olg] cirrnofine has been

forrnd. to be lower than those for the photocatalysed. cye1'i-zatLon of stil-

bene to p)eenanthrene.

21"

r"3 a

C.yc1izati.on of stil-bere.

Ihe photoeycLization of stilbene to phenanthnene is generally

thougtrtS'1ot11 to occur by the internar coupling of a d.i¡aclica.l- (5t).

In the cis-trans isome r,zatíon of stiJ-bene Schaffn""T n"onosed. a coffinon

excited. state intermed.iate (fi) which had. the gþ-configuration. The

intermed.iate wouLd. have oth¡er resonance for:'ns or¡e of which ttras (51+).

+

$Ð (¡+)

-,It was praposed.r that this i-ni;e:xred.iate resonance form q¡rc!ízed. to give

þrl+b-dihyd.rophenanthrera (Sg), which was d.ehyd.rogenated in a dark

reaction to give phenantlrrene.

fhe initial suggestion by Schaffner7 has been refuted. byo

$tegemoyer'vÈro obsenred. that initial- rate of formation of phenanthrene

from trans-stilbene was zero where as from cis-stilbene it was fj¡lite"

IIc LeIü. tl¡.e viev¡ Lh¿L'Lhe cyc;U.za'bj-on of t¡'arl;s,-sLill¡e¡re sÌ:.c¡uId proct;ud.

vig arr excited. state available only to cis-stilbene" He further p:roposed.

that the excited. singlet state corrtd. be repre,sented. by the dirad.ical (54)

ï/hicÌÌ cycJJrzeð. to give the d.ihyd.rophenanthrene (59) and. then und.e¡went

22"

d.ehlyd.rogenation to give pherranthrene.

frrad-iation of c:is- or @anq-stilbene in the absence of art

oxidant failed. to prod,uce any pherra:rthrene but resultecl in cls-tz'ans

equilibration viy'cually without ar¡g loss irr the total amou¡:t of s'cil-

bene.11 t1)+ Ilence the ô.ihydrophenanthrene intezmed.iate (¡g) no*t i.:nde:'go

rj¡rg.opening under these concÌiti-ons at such a rate that the stead.y state

concen'uration of this in';ezn:ed.iate i-s Iow relative to that of stilberu.'4

Ev'rdence hr" b""rr*å*t?1" trr" thenr,alú1 trrd. peoiochenti.uZ53 ri:rg open-

i:rg of the &ihyd.rophenanthre"* (Sg). Àn exception to the non-clcllzation

r¡icler anaercbic cond.ítions has been for:nd v¡hen trvo strongly electr"on

attracting groups are on ë¡Ci!-positionso In such cases double tautonerism

occurs in the d.ihyd-rophenanth¡ene intermed.iate to prod.uce a ) r1O'. 18

C-ihyd.rgphenanthtene o -

Moore .t uL.1'l ot¡tained. further spectroscopic evid-ence for

the existanoe of U]*"U""nnenanthrene intermed.iate j¡r the eyc'lízatton

plocesso A yellovr substance vrith à ^u*

&7 mP v/as prod.uced on irrad'iation

of giÊ- or jl3lg-stilbene jn degassed. solutions with nravelength less tha¡r

J1O my. Sr.:bsequent exposure of this yellow solution to air causeô C.e-

col-ourization to give phenanthrene a¡d. it d.isappeared graclualiy in the

absence of ar¡r oxidant to give mainly c'is-sti1ber,e.11 Mo"" recent evi-

d.ence both for the structure of d.ihyd.rophenanthrrene ar¡d the role of orygen

has been reported by T,:o=rnrt?l'' Soiutions of 2r2t-, +rl+t-o 6r6r-hexa;re-i;h}I

stif-oene (55) on iruacliation even irr the presence of an oxid.ant aff'orccå

a reC compor:nd assr:¡neCr -r,o be l rjrL¡arLy'or6r8-hexamethyl À-arbb-d.iJayCrc-

pleenanthrene (56). lhe stabiJ-ity of thj-s compowrcl is explained. by the

absence of þ- and. l+tr- hydnogens.

2.3.

I{e

+

Me

I¡leMe Me

Me

Me Me

$s) $e)

lhe &ihyd.rophenanthrene (59) fozmed durj-ng j-r¡acliation of

gþ- and. trans-stilbene i.s beli-eved. to undergo tn'o successive abstrac-

tions of the d.oubly a]þIic J¡a- anfl l+b-hyd¡pgens j.:r thre presence of

oy-ygen to gir¡e phenanthrene" lhe p¡esence of hyd.rogen peroxid.e in

irracliated. solutions exposed. to air has been aetecteA]l

Ma11ory and. coworku""l0 fu.rro.,-=d " jrc-configuration for

the two tertiary lgrd.ncgens in the d.iåyd.ropherianthnene i,nte:med.iate

produced. in sol,ution" Srinivasan and. Pounu""tr2 f.lro,o a cis-configuration

for the d.ihyd,rophenanthrene fomed in vapour phase but.there is no d.:irect

evidence j¡l either câs€o Sargent an{ limmoJ"B *iro isolated. 9 r't}-

C.ihycì.ro-!r10-d.:ic¡'annphenantJrrenn foJlovri:rg the irradiation of õrøs-

d-ic¡'aneuSilbene in d.egassed. soiutions favoured. a cis-configuration for

9r1O-hyd,rtgens after rtolrlero stud:es of this compor:nd..

f,he @-configuration for lr-a¡4b-hydrogens in d.ihyd.rophenaJ!-

24"

threnes is d.eferd.ed. by ltattorylo'1L ot steric grounds and. by the expec-

tation that a cis-configuration lvouLd rridergo spontaneons d.ehyd.rogerstion.

AIso ana-logousi photochen.r.ical cyclizailion of 2sfsí-octatriene (57) tras

6zbeen shown-- to give trans-1 ,2-d.i-urethylú+,3¿5-cyclohexad.iene (¡g) "

-\--

Me

Me+

Me

Ir{e

$t) (la¡

Photocyclization of stil-bene to di-tryd.rophenanthrene is be-

1ieved.1L to occur from a first excited. singlet state of cis-stj.lbene.

The evid.ence put forward. for these arguments were that large concentra-

tions of d.issolved. ozygen d.o not inhibit cyclizatíon and. that the forrna-

tion of d.ihyd.rophenanthrene is not obse:¡¡ed.5J "À."r,

triplet state stilber¡ea

is prod.uced. d.irectly by enerry tra¡sfer from/wtde variety of triplet-

state ¡ùrotosens ítiuere.57 The overall reaction in the photochemical

cyelízatíon of gig- and trans-stilbene may be shown as j-n Scheme 1o

'C¡¡clization of diphenvlarn-ines,

Diphe4ylarnj.ne has been reported.2S to phot ocyc!íze to an

intermed.iâte which was foruml-ated. as dihyd.rucarbazole of the structure

(ZZ) cl.osely related. to the d.iJeydrophenantLrrene intermed.iate in the

cycLízatíon of stilbene. ThJ-s intermed.iate was observed. to t:rtd.ergo

25"

/\

(¡+)

\ ¡/

$t)

1v,

e

/

Oo

$g)Sckrere 1"

(+)

(zt)

Zoo

hy"

O2ê-

(60)

I't)IL

L-'

1L

HH

(4) (zz¡

I

RR

ring-spst'¡:ing to regenerate ôiphenylamine and. also to und.ergo aroma'ùiza-

tion to form carbazole (4). the similari.,ty of this reaction to those of

d.ihydrophenant}:¡ene is striking. HoweVer botlr reactions aze not analogous

as an ion:ic mechanlsm has roeen proposed for the q¡rc1-i.,zatíon of diphenyl-24

arn-ines. -'

Photocyctízatíon of d.:iphenylarnine involves a triplet-state

molecule' (60) wfrich irr_ turn is d.eriveC. by intersystem crossing from the

first excited. singlet state. fhe trrar¡si-ent d.iÌgrd.ro inte¡rned.iate (ZZ) cart

wrd.ergo conr¡ersion to carbazole (ZÐ t" two concurzent pa'chv'rays: one

pattrwqy requires oxygen as a reagent wl'lile the other involves a r:ni-

rnolecul¿r step with elimj¡ration of molecular hyd.rogen of very Iov¡ or zers

activation "n"rg;¡,?Ç'þ lhe assj-grunent of the structure (zz) for the

cyclized. j-ntermed.iate is supported. by the high acti.¡ation energr for

d.ecay and. by the formation of car'oazoLes in higþ yield. vuhen amines are

irrad.iated. in organic solvents exposed. to air.24

27'

Ç.vclj.zation of Sch1ff, bases.,

By anaiogy rvith i;he pirotocyciízation of cís- ¿rrc^ tra-ns,-

stil-bene which has been dennonstrated. to occur onJ'y foIlov,'i-ng the phc'oo-?,t,

excitation of gþ-j-somer anì not the trans-isomer¡ Mallory and. Trlocå'-'

suggested. that the cycl-i-za'cíon of Schíff base also might be expecceC. to

occur on\r on photoexcitation of the gig-isomer" Since 'che photo-

conversion d.oes r¡ot occur in ihe absence of o4ygen it was sugges';er7¿ ri|

that the reaction proceed.s by the way of an intermed.iate dj-hyd.ropheilårt-

'ohrid,i¡ie.

lhe small,er quantum yie1d. observed. for photocyclízatíon of

Schiff base was attributed. to various reasonso .Ihe thermal isomerizatíon

oí'benzalanjJ"Íne is found. to be extraozdinarily fast; the half life of

the cis-isomer being about '1 sec. at rr¡om temperature" Althougþ the

t.{q4q-isomer of benzalaniline is lcnor"¡n to und.ergo photoisorneriza'uio;:r to

cis-benzala:riline the photostatiorrary SV¡ggæ concentration rat,io has

been fourld. to be extreme\r small except at fow temperatr:res.A0r4î

In the case of Schiff bases the }ov,¡es'o excited. state is of the

n î* t¡pe (on z.o) suckr that 'ühe lifetime of o'rr 7ro exci-ted. nolecui-es

wouLd. be prohibitively short as far as the cyeLízztíon is corÐerrie.ê." it

has been argued that stilbenes und.ergo this type of cycLization wi'bh+

reasonabie efficiency only when tliey are in'che lov¡est îfà'if excited.

singiet stateo Althougþ no spect:vscopic evid.e¡rce has been aô.vanc;ü,

Jaffe ancì cowork"*55 assignrnent of the o n Tf as the lor'¡est excitea singlet

s'ba-ce of benzaLanj-line ind:irectly supports the l-ow photo-reaciivity of

Schiff bases.

OQ¿-V þ

Cvclí.zation of azo'oenzçrnes.

It has long been kncwn ihat the irracLiation of azolcenzer,e ín

neut:.al solutions or acetic acid. resul-ts in gÞ-jrans isomerj.za ti.or,o\)'

[he photostatÍonary composition r'¡as fourrd. to be indeperrC.en'c oÍ' thec(

ini'cial- conçosition or ligþ'c iróensity but d.epend.ent on vravelength""

Sj¡rce the sum of '¿he quantunr yieLds fo" gþ-.!gg4g isomerization is l-ess

than unity, it appears -ühat 'r;here c¿tr¡oot be a cor¡unon excited sta'ce

irrespective of wl::ich isorner is excite,L.58 Stuclies of the isomerizationÁo

at lov¡ -i;emperatures" supporteC L)nrnenmrrî s suggestion that the iso¡',rezi-24-

tiorr is a therma-l- one occurri-ng bet'ureen i;he excj-ted. ci.s- ancl trans-stateo

Althougþ stilbenes, d.iphenyl-anrines and. Schiff bases undergo

pho'tochenrical cycli.zati-.on in orgarric solvents, azobenzene d.id. noi: cyclize

r¡nd.er these cond.itions.T'58 The fai-l-ure of azobenzene to photoeycAíze

in neutral solutions 1,¡ras attributealh to the lowest excited. state being*+

of the n T type rather thar¡ tlne Ti->îf type, which j-s apparent3-y

necessary for cyclizatíon to occuro lrfte55 who examined. 'the spect:'um of

azobenzene irr organic solvents assigned. the longest.vravelength band. at

l€O mu to an n+'f* transition"

Hovrever the photolysis of acid. sol,utions of azoþenzene \Nas

eq cfr'uâeshov,al-' -to uÉd'erÊe cyclod.éhyd.rogenation reactions. Tlre longest r'¡ave-

lengtlr absorptJ.on band of aciclic solutj-or:s has been assigned to a fr-r¡i

tra¡sition ard. it was associa'üe¿60 u¿tt a¡r increase in basicity of ihe

exci'ced azabenzene i-n compari"orl ui.t¡. the gror.md. state molecule.

DA1/O

Analogous to the photocycllza+uion of stilbene i'3 i':.as been

9-7shol,¡ntl thr"t trars4,ci.s iso¡nerization must occur before a i'rars-azo

componnd. "r* I" rise to a cycLízed. prod.uct" A mechanisrn proposed. by

).trBad.ger, Drewer and Lewis"t' foÍ. the pho'cocyclízation of acid.ic soiutiorrs

of azobenzene is d.etailed- in Scheme 2. It is believed' tnaþ azobellzene

ín 22! sulphuric acid. is virtual-ly entiræ}y prrztonated. axd- that ti:e

cycls-zing species is probably a first excited- singlet s'üate j-n wrdch 'che

positivechargerepresented.originall¡lglltheprotonateôazon:-tro¿enin

the growr¿ state of the cJ-s-conjugate acid. (61) rnay be regard.ed as being'

more effectively shared. v.rith 'she ce.rbon atoms at the 2-, þ, ¿¡¿ $*.oositj-onso

The photo excitation of the ci.s-eonjugate acid- fbom the ground E-la'Ue 'c'o a

first excited. singlet state is shor',,-n by'uhe step (61) to (eZ)" Str"ucture

(62) nay therefore be consid.ered. arr importani exci'ced-state resoiiance

stzlcture arrd this is mechanistically significant jJ the rirrg-closure

step of this reaction invol,ves an excited. singlet sta'oe of ti¡e îf*'tf

t¡rpe" It v¡as therefore reasonably assumed. tha'c the cis-conjugate acid'

i¡r the photoexcited. state rindergoes ring closuze to give the conjugate

aci.d. of lOarlOb-d.iJryd.roberizoþ]cilvrofine (6J), whiclr j-n turn would ccn-

ceivably r:rrd.ergo two fast prototrapic rearrangenrents in succession for¡r-

irg .;he conjugate acid. of 5,6-d)hydrobenzolgcj.nnoline (6+). The ring-

closu¡e step is believed. to be irreversible and. the rate d.eterm'ining

etep. The tv¡o steps lead.ing io 5 r6-dÍhyr-rlr compor:nd. (64-) each iavoive

the transfer of a hyd.rogen atcrr from a tertiarXr carbon to a nitro3,err aiom

ai: ihis is regard.ed. as fasi a::Cr i¡'reversibL""31 5r6-litlyarc;oenzofl-

ci¡¡ooline i" fororo#Í to Ou very easily oxid.ised. and. in view of the

30.

I

22t

g

<hr>

__TH\-.F

+H

',-¡-

.L

10

)1IIv

6

(62(61)

21

o

(63)

4

\H H

+H

L¡:l

10b

(64)

Scieile 2.

(65)

H

J."

ei;ceptiona[y h:igh d.ehyoroge'rÐ."úion pov'¡er of azobenzene in strongly acid.ic

l*8 ^ t.,\solutlon- the cor¡jugate acid. (61-) is read.ily converbed. to'ohe fuily

aromatic compound- (65) on irrteraction v¡ith the conjugate acid. of azo-

be¡:.zene (61).

Ring-closure of a triplet s'riate of the cis-conjugate acid of

azobenzeîLe i-s consi¿.ered.J1 r.urlikely because of its relatively long life.

this could. l-ead. to jig -7

irans iso¡:erization arrd. hind.rance to riqg-

closure due to second,ary protoriation"

The effect of acidity changes on quantum yield's for the

cycLízaa;,íon of azobenzene v/as inresti-ga t"ð.u31 Increased. acid.ity d'e-

creased. the quantum yie1d. but jr¡creased. the yield. fraction. T,he d.ecrease

in quan'r;un yield. was explained- on the basis of second.ary protonation of

the photoexcited. conjugate aci.:ð. (62) occurring in competition vri'cìr ring-

cLosule. Thr,e protonati-on of the "p2

hyb"idizeð, nitroçn ï/as expec';ed. to

i-r;nilcit cycLízatíon whjJ.e protonation of "pJ hyb"i ùl;zeð. nitrogen v¡ould

conplete\r prevent ring-closure.

,Îhe effect of substituents on the quantum yield. of tJ-e cyc!íza-

tion of azobenzene also haÇ. been investigated.o A complete and. satis-

factory e>planation of the effects v¡as not possible on the basj-s of the

mechanism proposed. by Bad.ger, Drev,,er ancl. Lev¡is,J1 Of the t,¡¡o-sLrbstituted.

azobenzenes stud.ied. both L-chloro- and. ,l¡-methyl-azobenzenes had. tv,'o

tautomeric (títi and 67) gfå-conjugate acídso 'Ilre ratios of the t.,'¡o forrms

i¡ solutions ïrere un]ffoltâl and. a more critical exa¡rrination v¡as not possible.

A reasonal¡ie rationaltza'oion was nad.e for the 1ov¡er qua:irtum

cI (ivre)

32.

cl (¡¡s)

(et)

rp-substituent wor¡l-d. tend. to irùlibit

+

J,

(66)

yields for the cyeLj-zalLon of 4-chloroazobenzene and. 4-methylazobeztzene.

In structure (66) tlre + M effect of the chloro-substituent v¡or:-ld. red.uce

the charge on the protonated. n:itrogen and. hence also that at t}re 2-

positions; and the rj.ng-closure would. be hind.ered., i.iherelas in struc-h

ture (67) tne -l effect of the {1oh

develo¡xnent of a negative charge at the 2r -posÍtion which is assumed. to

be necessary for cyclization"' Sjmilar reasoning vras applied. to explain the lower quantun

yJ-eld. of J¡-methylaoobenzeneo In structure (66) the h¡per-conjugation

effect of the methyl group worild. hirder the cyclization. 0n the other hand.

in structure (67) tlre electron clensity at 2t-position would be sligþtIy

increased. by the + I effect of the methyJ, group ar¿d. would. enhance the

¡'aì;e of cyclization. It was assumed. ti:at protonation of l¡-rnethyLazo-

benzene gives pneferentially tlretautomer (66) a¡rd. this would. accorint

for 'uhe lor','er qr.rantuor yiel.c:- obse¡r,-eåo

C}I.APTT,R Ti

Photochernj.stry of Benzalarrj.l-ine and

other substituted. Schiff Bases

i-t1

9ffi A.røLar S,ulphuric Acid..

4).

Photochernistrr¡ of Benzalani-]-ine and- other su'i:sti-tuied- Schiff bases in

992 Sul-phuråc Aci-d.,

The photochernical- cyclod.ehydrugerration of stilbene to.lE

pherrar.threne'r in organic solvents anC of azolr,enzene to benz"[g3-

2642cirmoline-- rÉ i-n strongly acid.ic sol-utions has 'oeen shor',rn to be e. gen-

era-L reaction which occur-j w:-th :rnn¡r substl'cuted. stilbenes an,å àza-Ðë!:-

zeneso Attempts rnad.e to extencL this photc-reactj-on to Schiff bases Íor

the preparation phenanthrid.j:les, und.er the cor¡åiì;ions in wlúch stilbene

vras cyclÍ zed, to phenanihlene met ,,,¡i';h failu"."7011+/+Ð Îhe non-cyiiiza-

tj.on of Schiff bases wrd.er these conLitions v¡as satisfactorily acco¡:r¡,ted-

for stereochemicalLy"l4'3+ Ii hers been d.enor¡str¿teô ilrai phot ocycliza-

tion of stilbenetrl "rrd.

of azobenzene2Tc3l occurs onþ after the photo-

e;lcitation of the cis-isomer and not the t"rarrs-isorner. By analogy it

was suggested. tha'c the photocycAlzz'cion of Schjff bases rnight also occur

on\r through photoexcitation of the cls-isomer" The cis -V

f,rans,

isomerization of Schiff bases is extraorüinarily fast,r)û'4n the half l-ife

of the cis-isomer being only aìrou'r; '¡ seco at roon temperatr:re" A.I',:hoqgþ

trans-Schiff bases are l<noi,'u-n to und.e;'go photoisomez'izatj-on to gþ-for:n

the photostatiorrary _"ry¡ge5g ratio has been four,L to be ertnemely sinallr

except at lov¡ ternperati:res"i+0,ì l. zt.

Also i'o has been argueå"';'rr+ that in t!¡e case of anils the

]ov¡es-,, excited. singie-c state is of the n -,'rf t¡,pe such tha-b tÌre lifeiime

of the T s .ll' type excited. noLecul-es ,z¡ould. be almost prohibitivel"y short

zE

as far as cyaLization i-s concerned., olving to a rapirl. int,ernal conversion+to give the n ft excited. molecules. Ëlli1bene and. rel_a,ce¿ conrpound,s

urd-ergo photocyclization rv:ith reaso:rable efficiency only vrhen they are j-n

the Io'.vasi 1l tlf* excíted- singlet ui;u.ieollh The non-photocytclíza.tíon ofazoT¿enzene in organic solvents has also been

".-çl"1l9d- to be clue to the

Iovæst excited. state being of the n o' ,yn."trL

Hovrever when azobenzene .¡¡as irrad.iated. jn strongly aciiüc sol-vents cyclization took p!^.."27 It has been suggested'N/+rJ1 ti.u.t r¡ncter

these cond-itions the photoexcitation of azobenzenes:'prÐduce¿ the lovrestE

1l-> Tr excited' singlet state molecules ancl these und.erwent eycLi1zationo

the:efore it was d'ecided. to examine the photocyelization of Schj-ff bases

in aciðic solution where the catio¡r.s (69) derived. by the protonation ofthe nitzpgen '*rould. possibry not have aJr n -à tf state as their rov¡est

excited. state, but a T f* t¡4>eo 98lrt Lna:rar su]-phurj.c acid. r,.,¿;s chosen

+

+H

(68) (6e)

as the solvent as most of the anils are rapid.ly þ¡rclrolyzed,by acid.-.ueter

mirbuzes.6S

The j-rra.d.iations r¡erì3 car':ried. out j:r a ,,'¿ater*cooiecl P¡itex

apgaratus rrith a Philips lt):i ',21\';r. me-i'cury-qua:ri:a lamloo lhe lamp rras

surrounded. by a '¡¡ate;-jaclcei so tha'c ihe 1igþ'c passed. 'chrough l"¡a'ü3ï'

before j,t entered. the reac'¿icn r¡rixtrr-æ.

TT"'¡ Benzala-niline"

1¡'lhen a dilute solution o! benzaLa.niline (4 * lo-J g¡ tn 9Vl

- '1OO mJ.) was i:r:rad.iated. a slov¡ resillpriunc acra 1't0O mJ-) was i:r:rad.iatec. a slov¡ reaction n-.*ãuo The

progress of the reaction ¡¡¡as fol-lo'r,ved. fron the ul-t:caviolet spectra of the

irra.tl.iated. solutionso the main absorpiion band.s at' 2-16 mP and 3i€' rcr1

progressivety d.im'inisired. in intensity and. a nevÍ bar:d. at 2]+9 tî,j) grad.uali-y

appeared.o l/flnen ,no further change coul-rl- be d.etectea (72 nr) i-rr 'ci.ie

ultraviolet spectrum the ruiy.tui'e -.y"Ërs 'lvorhe'1 up" !-rpm the reaction pro-

ducts the cycli zatíon prod.uct phe;ianthzzCi-::e ( 70) v¡as obtained. in about

J&/" yieLð. along vrith benzylaai-Iine (/1) (g.1J,i6f yLeIð')" Ihe latter

was id.entified. as N-benzyl-NrNß-d.ipheqfithiocarba¡niae (72), vrhioh rras

formed. by cond.ensation lvi.t,L phenyl-isothiocyar¡ate" In view, of the fact

t¿\at the formatiory'tånryr^oifine (71), a re'åuction prod.uct, accompanies

th.e cyclizatioo of benzaLaniline, this Sciriff base appears to be ino-'e

closely related, Lo azobenzene a¡rd. its d.erivatives in its photochei'rricai

properties tJran to the stiloenes, .Lzo cornpound.s 'l',/nen irrao.iated. Ín

strongþ acid.ic solutions give rise to benzicline rearrarigement p"otl;..'r38-3o ú2

in ad.dition to benzo[g]cinnolines, but the conversion of stilbene to

prer:,anthrene appears not to be accornpa:.iieo by f ormation of biÌ:enzJùo "'

2-'tJls

-à+

(6e)

Qt) + PhNcs

->

Ph,ffi

+

( zo¡

N

I

Qt)

2

Ph

Qz¡

In tÌre photocatalyzeð. cyclizatíon of 1-naphthal-1 c-¡raphtlgrlanineSS inbenzene the presence of ðissolved. ols¡gen was shown to be necessaryo

Dispropor-tionation therefore d.oes not play an apparently significant

ncl-e in thi-s case.

Ihe qr:antr:m effÍclency of the photochemical reacti-on of

benzalaniline und.er these cond.itions appears to be rnarkeùLy lolrcr tha:::.74'that of azobenzere, ,in 2?g sulphuric acíd-/' but the two reactions are

otherr,rrise comparable.

rr.2 Other S chiff Bases

Attempts have been mad.e to exter¡d. the photochemical reaction

of ^oenzaLanili¡re ín 9g/" sulphuric acid. to other Schiff b¿¡.ses for the

pzeparation of substituted. phei"ranthrid.ineso Hovrever none of the Schi-ff

38.

bases examined. couId. be induced. to und-ergo photocycJ-l,zatilon under tl¡e

conôitior¡s in which benza-laniU-ne cyclized. to give phenanthridine.

Thus 4-methylbenzalaniline (T, g = Me), benzal-þmettrylaniline (7t¡,

R ' Me)r Þchlorobenzalaniline (7j, n, = CI), ard benzal-lrchloroaniline

(7+, n = CI) failed. to cyc!íze on jrad.iation LrL 9æ/" sulphuric a.cid.

RR

+

Qù B = cr orMe

R

+

(Z+) R = cI or Me

The bis-anils benz aL(þbenzalanilino) aniline ( 75 ) anrl te naphthatat-

d.ianiline (16) a-Iso cou1d. not be induced. to cyclize. The irrad'iations

werv car.r.ictL out 'tlr ,Jìlute solutions ( 1-? x 1O-fD s.t room ternperature.

The absorpti.on band. at the lorvest uavelengt h (J4È360 mF) assigned64'65

,fto the 1f -, T transition in the Schiff bages, grad.uatly d.ecreased. in

39.

\+

+ -X+ AD

\

Qz)

f

@+

Qe)

intensity with respect to the band at 27C' 280 m¡ regíon as ir¡ad.i'ation

was continued. No new peak was fonned j¡ the 2)+5-255 m¡ negion howevert

as was the case with benzalarriline. Prolonged. ir¡:ad.iation r^esulted. jn a

consid.erable a¡nor:nt of cha¡rir¡g, md tltis probabþ grad.ualþ d.estroyed.

the a¡its. No cycLízeð. pmd.uct could be isolated. from the irrad.iated.

solutions.

'llhe decrease i¡r the intensity of the band. at the longest

wavelength (llp - 36O ny) in these cases may be attributed. to tlre d.ecrease

in the nwnber of molecuJ"es of Schiff bases which absorl¡ in this regíon,

ì(+

4oo

as a nesult of grad.uat l¡yd.rolysis in su.lphuric acid..

It is not fully und"erstood. r'dry these substituted. Schif'f bases

resi,st photochemical cyclod.ehyd.rrogenationo The enerry absorbed. by a

molecule during irrad.iation, instead of resulting i.n photochemical r€ac-

tion, could. be d.issipated, by various non-prod.uctive prccesses such as

internal" corn¡ersi-on, intersystem crrcssingr self-quenching, fluorescence

or ¡ùosphorescence.

It has been obser"r"d3l that the stùsti-tuents in azoberrzerLe

had. a prÐnounced. effect on the rate of cycLi-zation reaction and quantun

yield.. I[hen azobenzene is su]cstituted. with a chloro- or nethyl-group in

þposition it was obse¡ved. that there vras a marked. decrease in the guan-

tun yield. and in the rate of reaction. Since the quantum efficiency of

the photochesúcal cyclization reaction of ber¡za1ar:,iline was apparr:ntly

much lower tk¡an that of azobenzene ir, 2ë sulphuric acid, it is asswned.

that sr¡bstituted. benzalaniline will have still folver valueso In view

of these facts and. that Schiff bases are wrstable and.'a:rr grad.ually

lSrcl.rolysed. in the presence of water (above o.ugùl*l it is reasor¡able to

assume that these Schiff bases were grad.ually d.estroyed. before ar¡r

d.etectable amount of photocycl,ized. products were formed.

Eisher anA ¡'rei40 observed. spectral changes when benzalaniline

was irrad.iated. at very low temperature* (-tOOoC) and. these chartges vtere

ascribeô to the photoisomerization of the @Iå-isomer to the cís-isomer.

the activation energy for the d.ecay of glg -+ tra4s isomer was about

1I¡.2-17 koal molo-1. Hence i-f the imad.iations of Schiff bases are

+1.

carried. out at such lorv temperatures at which the photostationary

S!y'j!""g ratio is higþer, it rr.ight be possible to induce cyclizatioris

of these Schj-ff bases. Such experjments have not yet been ma.de.

Cava and. ScLr-lessing"rrSB who obse¡ved. the cyclization of

1-naphthal--1 t -naphthflami¡re to d.ibenz"[gé] phenanthridine in organic

solvents exposed. to air, favoured. a mechanism ana-logous to that of the

eyc!ízat,j:on of stirbene to phenanthreneo Mar1ory et alo ,34 ^ft.r their

stud'ies on tho photocycllzation of benzalar:;iline and N-d.iphenylmethylene-

a¡riIine, aJ-so favou¡ed. the same mechanism for these reactionso A

hy\ O2+

Qt)

d'ihyd.rophenanthrid.ine inte¡med.iate (77) ,r"" bel-ieved. to be formed. in the

cou¡se of the reactiono

Bad.ger, Drewer and. LewisSl y*u. postr:lated. a necha¡isn for

tlre cyclizatLon of azobenzene in strongþ aciòic solutions, vårich has

been d.ealt with in d.etail in ths preood.ing rcvicwo sincc thc photo-

cycLization of be¡rzararü-Line in l8f sulphurio acid. appears to be a

d.isproportior¡,ation reaction akin to that of azobenzere, it j.s suggested.

)+2.

that the nechanism of cyclization of benzal.aniline fol-lor'æ a sjrnilar

Inttenl. Further stu&i-es are essential before a d.efinite mecha¡rj.sm

could. be pncposed,

43"

ExperimentaJ.o

9grgrg!.

Melting points were d.etermined. in capillaries j.n a Gallerùcamp

melting poi.:nt apparatus and. are uncorrected.

Ir¡frared. spectra were d.etezmi.ned. with Perkin-Elmer 137 arLð,

ZJJ spectrophotometers.

Ultraviolet absorption stræctra were d.ete¡¡nined. with an Optica

CF, recorriing speotæphotonreter or a Perkin-Elmer lJ7 ultraviolet speo-+

trophotometer"

Unless othenirise stated., the ligþt petroleum used. had, a boiling

range of 110-600.

All orgalric solvent extracts were d.ried over anlryd.ror.rs mag-

nesiun sr:lphate.

Microana\rses were oa¡ried. out by tkre Australian Mj.croanalytical

Senrice, Melbourne.

Irrad.iations wÍth a Philips 1251M h.LdfL pressure mer¡cury-quartz

lamp we:re carried. out in a waterÈcooled. Eyrex apparatus. llhe lamp was

surround.ed. by a cyli-nd.rical. waten-jacket which ras i¡r turn surround.ed, by

a jacl<et containing the solutiono

I¡rad.iations ìiv'ith sr.rnlight wene carried. out in a stoppered.

Byrex cultu¡e flaslc"

l+4"

Preparati.on of Schiff bâses.

All tkre requlred. Sch:lff bases were prepared" by the condensation

of the appropriate al.dehyd.e and the amj¡reo The prod-ucts were repeatedly

crystallizeð from ethanol-benz,erÊ nrixtures to rernove ¡ll the unchanged

reactants. Ana\rbica-Ìly pure samples 'were used for i:rad.iations"

Benzalarrlline.

Benzalaniline was obtained. a.s pale yellow crystals by the con-

d.ensation of benzald.ekryd.e and. a¡jJ.ine followed. by crystùJizatíon,

m,p. 5r+o (lit. ,66 5Lo) "

f ÞMe t hvlb enzal] aniline,

Cond.ensation of ¡-toh:a1d.eÌ:yd.e ard. aniline follovred- by crystalliza-

tion of the praduct affo¡d.ed pale yell,ovr ciXrstals of þn^.cthylberwal-

anil.ine, nepr L7o (tit" ," M.r-Lr8o).

B e nz aL- l*-ne t h.vl a¡-L 1 ine .

Benza-1d.ehyd.e a¡rd. ¡-toluiline ï'¿eæ conclensed. and. the product ob-

tained. was crystaLhízeô. to give benzal-,lrrnetþlaniliner m.p. 36? çirit"r66

t50).

@.4,{hlorobenzaldeliyd.e a¡rd. anjJ.ine vrere condensed. arrd the product

obtained. on crystalJ-ization gave [rcb-lorp¡enz^1J aniline as pale

45.

yellow flakes, m.p. 660 (tit. ,66 66o).

B e nz aL-.f-c hl.o ro aniline .

-

Benzaf-lrchLoroaniline was obtained. as crealn coloured. platesby crysta-llizing the prod-uct from the cond.ensatj-on of, benza-ld.elryd.e and.

þchloncan:iliner ilop. 6z0 (tit"167 6ro¡.

B enzal ( L-be nzalanil ino) aniline .

Benzal'(Þbenzalanilino) an:-tine rïas pnepared. by the cond.ensa-

tion of benzald.ehyd.e a¡rd. ¡-phenylene di an¡_i-ne. The prod.uct crystallized.from ethanor as pa-le yelIow platesr n.p. 1à¡o ( Lir.r69 iJg-1{o1.

I e raphth al- ald.ianil ine.

An ethar¡olic soLution of teraphthala-1d.ei1yd.e a¡rd. aniline were

wa¡rned' on a water-bath for fifteen minutes ard. the prod.uct formed. v¡as

collected' and' recrystallized. rxrtil constant nelting point .was e¡a*'n"u.Teraphthalald.i^an:rline was obtai¡¡ed, as ye11ow plates, m.p. 1650 (irit. r7o16t*-t65o).

Irrad.iati-on of Schiff bases

Berøalaniline-

, A solution of benzalaniline (76 mg) ín )$ A¡r¿I¿rr sulphur{-c

acia (100 rrr1) was irrad.iated. in a Py:rex *r."to" with a mercu4l-eu atrz lamp.

The reaction was followed. by the chariges in the uLtraviolet spectnm.

ùß.

l'Íl:en there was no furtl:er cìlange in the spectrum (7e ¡rours) tt" nrblcu¡e

was d'j'luted' with ice and. basified. with sod.j-un hgrdroxid.eo The basified.sorution was repeateùry extracted. with benzeræ. Evaporation of thesolvent yielded, a brovrn-yeLlow g.xn (58 mg) which was ¡"¿1"soIved inbenzene and' chromatographed. on a column of silica. El-ution with a mjx-tuæ of ether (lØr,v:v) and. benzene caused. the ben4rlaniLine to separateas the fir"st band (yellow fLuorescence) o The residue obtained. on eva-poration of the first chromatographic fraction was i-d.entified. as ben4¡1-aniline by its conversion with pherSrlisothiocyanate to NrNr -d.iphenyl-N-ben4¡r thiocarbamid.e, m.p. loTo çtit.r71 two)o Mixed. ¡n.p. with an

authentic sanple d.id. not d.epress the melting point. The ir:frared. spectraof both the samples weæ id.entj.cal,.

The resj-due (29 nù obtaj¡red. after evaporation of the secor¡d.

fraction was i.entified. as phenanthricl:i¡er ü.p. lOJo (Iit "17, ,Oho).Ad¡nixtur¡e with an authentíc sample did. not d.epress the melti_ng point.The infra¡ed' s¡æctra of both the sarrpres were id.entical.

I

Irrad.iations other substi-tu Schiff SES

Each of the forlowing schiff bases in the quantity stated.below was rtisserved. in gt/, Axtalar sr:lphuric acid. (100 n_r) arul was irra_d.iated' for the ind.icated. time in a lyrex photochemical reactor wÍth a

125w },'íøÀ pressure me¡oury-qvartz Iamp. The reaction was followed. bythe changes in the ultraviolet spectra at &ifferent inten¡als.

47"

lL-Vet frvlbenzal-l aniline -

tÞlt"tnyfbenzal] a¡riline (Lt *g, Z x 1O-3 U) ,n"." irrad.iated.

for JOO hourso rhe initial main absorption peal< i-r, lrr" region of J6o ny

grad.ua-lIy d.ec¡eased. i.n intensi.ty. No new band.s were fo¡med. ard. no cyclized.

prod'uct could. be obtained. on working-up the rnixture as in the previous

erperjment.

B enzal-l¡--me thylaniline -

Benzal-ÞmetþIaniline (41 mE¡ Z * lü3 U) *"" irrad.iated for

250 hourso The interisity of the main ¿þserption p"-* of the originalsolution in the region of 355 m¡r gradually d.ecreased. d.uring j-rrad.iation.

No cyclized, prod.uct could. be obtained. on working-up the reaction m_ix-

tureo

fÀ-Chlo robenzaÐ an-i1 i ne .

[4,cirrorobenaal] arriJ.ine (\6 ^e, 2 x 1O-' U) was irrad.iated. in

sulphuric acid. for 260 hor:rs. In this case afso tf,"i.in absorption peak

(:æ *¡.) j¡r the origlnal spectn:n'r grad.ually decreased i¡t intensity as

irrad.iation was contjrrued.. But no cyc))za.tion pncd.uct could. be obtained.

on working-up the reaction mixtu¡e.

D c u.z aL- )+-ch]-<.r ru aniL lne

Benzal-\-chlo¡r¡ar¡iline (46 *g, 2 x 1O-J Ð was irradiated. for

268 hours. the longest wavelength absorlption fou¡d. initially at Jli,B m¡

grad.ually d.j¡¡rinj-shed. in intensity on irrad.iation and. the sulphgric acid

48.

solution turned. d.arl<. 0n v¿orking-up the reaction mixtu¡e rn cyclization

product could. be obtained.o

B enzal ( 4-b enza]-anilino) anil ine.

¡enza-1(4-benzalan:jJ-Íno)ani1i-ne (28 !€, 1 x 1ü5 lj) w.. irra-

d.iated. in sulphurj.o acid. for Ð6 hours. lhe longest wavelelgtk, "lsor¡l.-

tion peak fourà before i-rrad.j.ation (¡60 m¡.r) gradually d.ecreased. in j-nten-

sity anl the sulphuric acid. solution turned. d.arko No cyclized. prod-uct

could. be obtained. when the reaction ¡'üxtune v¡as worked.-up.

T e raphth al- ald.ianiline .

Teraphthalald.ianjiline (ZB mgt 1 x lO-3 {ù *.= irrad.ia.ted. in

sulphuric acid. for JOO hours. The longest *.rr"f".rgth absoxption peak

(560 m¡r) for¡nd. initial'ly gradua$r ùinl-inished. as i¡rad.iation was contin-

uedo Hene again the sulphuric acj-d. solution became very d.ark in colour

a¡r¡1 no cycJ-ízeð. prod,uct could. be isolated..

CHAPTER TTI

Photochem:istry of Am:lno-, Nitro-, ard'

Acetyì'-Azobenzenes

9V" Sulphuric Acid..

tn

49.

N Ace L-Azobenzene

Acid.,

rrrol @.The photocatùyzed. cyclLzatíon reaction of azobenzene has been

four¡d..to be a generral reaction and. the cyclo d.ehyd.nrgenation of rnany

substituted. azobenzenes have been investi-gated,.26-32 Ihe substituents

have been for:nd. to exèrt a profound. effect on the rate of eyctizatioå.1

Chloro-, carbo>y-, iodo-r ar:d. metliyl-substituted. benzo[cl cirueolines have

been successfirlþ preparred.zS'29 Uy the iread.iation of the corresponding

substituted. azobenzenes i¡r 2ry sulphur:ic acid. 0n the other hand. pre-

Ii:ruinary qualitative experiments suggested. that strongly conjugating

substituents inhibit cyclod.ehyd.rogenation and. no cyclod.ehydrogenation

coul"d. be d.etected. fotlowing prolonged. irrad.iation of Þarrinoazobenzere,.o

or of 4-d.i¡netWlaminoazobenzene 'itr zry sr:-lphuric acído*t

It has been shor¡rn in the preced.ing chapter th¡at benza-lan-iline

nnd.ergoes cyclod.e\rd.rogenation when ir:rad.iateð, in 9gÁ sulphuric aci<i.

Tlris cyclod.ehyd.roge¡ration was slow compared. to that of azobenzenel

however tkris reaction also seems to involve a disproporbionation as benzyl-

aniLine was fo¡med. in ad.ùition to phenanthrid.ine. It y¡as therefore of

interest to i¡rad.iate Þbenzala¡rinoazobenzern (JB) and 4r4t -bisbenza-l-

aminoazoberLzene in concentrated. sulphuric acid. and. to examine the prrcd.ucts.

This chapter describes the stud.ies on the irrad.iation of 4-benzalamino-

azo'oenzene, )+r4' -bisbenzalamj¡roazobenzene, J-arnino-, and. J-benzalarnino-

azot,ertzene and. of 3- and. Þnitro and acetXrLazobenzenenesr. in concentrated.

50.

sulphuric acid.

Altbough þanuinoazobenzene could. not be induced. to undergo

protochemical cyclod.ehydrogenation, it seemed. J-ike1y that the formation

of the Schiff base worrld. so mod.ify the electronic effect of the sub-

stitr¡ent that cyclod.ehydrrcgenation to a sr:bstituted. lenzo[g)cj:rnoline

(79, nrn' c N=CIÍ) nr:ight occuro However, as benzalanjJ.ine ha,s been shovrn

to und.ergo photochemical cyclod.ehyd.rogenation, the formation of a pheryl-

azophenanthrid.ine (80, RrRt c N*N) follovrj-ng the i-rinadiation of À-

benzalaninoazobenzene (78) was a-lso conceivabl-eo Moreor¡er if two cyclo-

d.el¡yd.r"oger¡ations cor¡ld. be brought about, a tríaza-1 ,2i5 rí-dlbenzanthra-

cene (81) *teþt nesulto

( za¡

Qg)

(er)

\

(¿o)

51.

It was forxrd. that rvhen t¡so azo linkages are present as in l+=

pheryLazo azobenzene ($) and. 4r4t -bis(phenytazo)uipher6rlmethane (¿6 ¡

R = CH2) cyclod.ehyd.rogenation can occur in one half of the molecule and

red.uction in the other half as a result of irrad.iation ir\ 9g/6 sulphuric

^"ytr.3OúZ Îhe formation of two such products, one (79, Arnl = -NH.-Ctfz)

with cyclir,atJ.:on occurrjr:.g around 1.ine azo linkage ard. cortcom:itant reduc-

tion occuffing at the Schiff base linkage and the other (BO, RrRt = -NIl-Iüf-)

witle cyclization occurring around. the Schi-ff base and sinrultaneous red.uc-

tion occu¡ring at tine azo linkage, r¡rere also conceivabfe.

The l¡-¡snzalaminoazobenzene provid.ed. also a systern to cornpe.re

the reactiwidy of the azo linkage and. the Schiff base linhage towards

photocyclízal,ion.

The photocyclízatíon of azo compor.¡rrd.s to benzo[g]ej¡molines

is very easily follorved. spectrophotometricully.z7 In the case of azo-

benzene, for instance, the broad. absorption band. at' lQO m¡: in 24 suJ'-

phuric acid. is replaced. by peaks at 252 anÔ. 365 m¡ typical of' benzoffl -

ci-r¡noline in acid.ic solutions. The bleachi-ng of d.ilute acid-ic solutions

of azo,compound.s (spectroscopic concentrations) on irrad.iation was also

i-nd.icative of tkre cyclization.

[rhen d.ilute solutions of 4-benzalanuinoazobenzene ir\ 9g/á

suJ-phuric acid. was erçosed. to sunligþt, a grad.iral bleaching occurred-.

The r:J,travj-olet absorption spectrum shorved pealcs attributable to eyclizeð.

products. Before irxaùj-ation the main peaks i¡l the uitravioiet absorption

spectrum were at JJQ and. )+52 my. Äs the irrad.iation was continued the

EO

strong peak at 452 ny graciual-Ly d-i-,r:inished. i¡r intensity and a nevr peak

arpund. 25O rryt appeared j¡rd.icating that cycLizaLion hacL occurred."

, i?hen A-benzalaminoazobenzene (f g) in 9&l sulphurio acid.

(teO ^f) was irracliated. vat?r a ILPK 125 tr'tr. mercury-qwartz J-amp in a Pyre:l

reactor as a preparative scaie experjrnent tlre reaction proceeded. very*

slolvly" ï¡Ihen no furl*rer change couJ.d. be d.etected. j:r the ultrz-violet

and. visible spec+.rum, irraclíation'was terrrinated., and. 2-a¡linob,e*o|S)-

cinrroline was obtaj¡.ed in almost quanti-tative yield., together with some

benzalclehyde. No other prod.ucts v¡ere detected Ín this :ceactiono It

mu¿t be conclud.ed therefore that the photocheraical cyclod.ehyd.r-oge:ration

of the azobenzene parb of the molecuJ"e occu-rs very much more reâôily

than tlrat of the benzalaniline par-t. '

The hígþ yietd. in thís reaction occasioned. some surprise.

I'ihen azobenzene vras irrad.iateà i-n strongly acid.ic solutions benzo[g] -

cinr¡oline was fowrd. to be prrcduced. i-n about J€1/o yirelrd..28 the other

product, isolated. in sligþt1y lower yj-eId., was benzid.ine" In l-ater

e:<periments it has been shovrn that the yield. of benzol9 cinno]-ine d.epend-s

on the acid.ity of the *"d.i*.J1 As the acJ-d.ity vras increased, the quantum

yietd- d.ecreased" but the yietd. fraction of benzopilcir,noline increased.

I'ihen azobenzene viras irrad.iatel ín 98/" sulphuric acid.

benzof cl ciruroline was obtained. in about 60'16 yie1;ð., md no benzi-dlne-L-/

Ly¡e r.eatr.r,a.rrgeurcrrt prod.ucts coul-ù L¡e cLetect "ð,.57 ft has bccrr cugg""t"d.49

that for irrad-iations of azobenzene carried. out in strong acid', the

kgrd.razobenzene first formed cou1d. possibly undergo d.isproporbionation

5i"

to form an:iline ancl azobenzet\eo ÎÌre azobenzene so prod.ucecl wou-Ld- then

enter the cycle to yietd. more benzol's:lcinnoline and. 1¡rd.razobe'îlzerte. ffd.isproportionation of the hyd.razobe nzerle, formed. d.uring imad.iation,

occurred' in excl-usive preference to benzidine-rearrangement a limitingyield. of only 66.66% of the cJrclizecj prod.uct would. be expected..

The appárent absence of any benzid.ine-type prod.ucts and the

slow evolution of sulphur d-ioxid.e noted- during the i-rracìiation ef 4-benzalandnoazobenzene suggests that the tvro hydrogen atq"ns liberated.

d'uring the cyclizaiíon a¡e oxid"i-sed. by concentrated. sulphuric acid..

The photochernical- cyclocìehyd.ncgenation of 4r4r -bisbenzal-a¡nino-

azobenzene (eZ) also proceed.ed. slorvly anð, 2r9-dia¡Énobenzo1g)cinnoiine

(BS) was isolatecl in goocl yield.. rn üris case a-lso no benzid.ine-,üJrpe

prod-ucts, phenanthrid.ine d.erivative or the d.oubly cycJ,i-.zeð. procluct coul-d.

be i-solated."

Ualike,l¡-anr:lnoazobenzene, J-aminoazobenzette (St) was found. to

wrd.ergo reaclr cyclod.ehyd.rogenation by irrad.iation of j.ts solution ín ){fsulphuric acid.. This cyclizaa¡ion cou1d. conceivably occur ai eíther 2-

or 6-positíon to give either 'i-aminobenzo[glcinnoline (86) or J-arnirto'oenzo-

fcl cirmoli]1e (85) o Hov¡ever, the cyc:rj,zatíon into the 2-posj-tion would. be

sterical-ly hind.ered.o tr ollovring the irrad.i-ation of J-arainoazobenzene ,

J-aninobenzo[glciruioline was isolated. in good yieid.; no 1-aminobenzolfl-

cinnoLrne cou.Ld. be detected.o The irracLiation of Jåenzal-a¡uinoazobenzene

(gZ) in concentrated. suJ.phuric acid. al-so likev¡ise yield.ed J-arninobe nzo:Fi--

cin¡roline irr good. yie1d."

( e2)

54.

EzN

_>

(81)

HeN

(s6)

NH2

(e¡)

2

2

-(e+)

(ez) -> (e¡) + c6H5cHO

55.

þ,Lmincazobenzene and 4r4' -Ciaminoazobenzerre therefore d.iffer

from ,la-benzalalrLinoazobenzerte, )+24.t -bi-sbenzala:tinoazobenzere and J-amino-

azobenzene in that they resist photoOaenrical- cycJ-cdehyd-rogenation and. it

is interestj:rg to speculate v,ùry this shouLd, be soo It is possible to give

a somelvhat reasonable ans'¿¡er to this query with the present lmovrled.ge of

the reaction mechanism postulated. by Bad.ger, Drel'¡er arrd. Le'lris31 fo, trr"

photochem'ica1 cyclization of azoben zerLe .

It has b""n "hou¡nil

that an azo coneou¡ô must ad-opt the cÍq-

configuration before it can urdergo the cyclod.ehyCrogenation :'eactio:r.

and. that argr factor, tkrerefore, which recluces the stability oi'the cj-s

forn by lovrering the bond. ord.er of the azolinJrager-vriII also reduce the

rate of cyclod.ehyd.rogenation. There is liitie d.oubt that -þanÉrLoa.zo-

berøene exists in concentrated- sulphur:ic aciC. as the d:iprotorøted- speci-es

(88) arrd. this would. very probably give rise to a prototr,opic equiJibriu¡r

rrrixture (88=:89). The expected electronic interactions (shown by the

curved. arrovrs) ind-uced. by the powerfuJ. e-lîecí of the protonatrúed amino

group in the benzenoid. d.icatic¡n (88) vroufd. reduce the bonC ord.er of the

azo linkage very substa¡tiaÌly and. 'vyith isomerízation to p-quirå;rloia

dipation (89) the stability of the cís-fo¡m v¡ould. U" ""¿rJ"d.

even furthsr.

The photostability of l¡-arninoazohenzene rnaJ/ well be the result of these

factorso 0n the other harrd., i;he protonated. benzaLarnino group of the d.i-

cntion (90) rìeri ved frorn /¡,-benzal-ami¡roazol-lenzene woul-d, not he ex¡ecrteri-

to have a rnarked. infl-uence on the azo linkage, as the positive charge

56.

H + H%7J

( ee) ( eg)

on the benzalamino nitrogen atom v¡ould cause preferential electronic

interaction with the benzilid.ene group. Hence tbe photoexcitation of

the d.ication from the ground. state to a first excited. state could. be

shorvn by the step (90) to (gl). It is then reasonable to assume that

H\ +

+

(go) (e1)

this conjugate acid. in the photoexcited state can undergo ring closure.

The same argument is applicable for the non-cyclization of

414'-diaminoazobenzene in 99" sulphuric acld.. the protonated 4r4.-

5'7"

d.ianrinoazobenzene would- very likely gj.ve ri-se to a prototropic equilibrium

mixture (92) and (91). Îþe expected. electronic interactions induced. by

++ +2

H7 Itr++

IÐN

2

+He*

+

( g+) 0z¡ (g:)

the povierful effect of the protonated amino g"oups in the benzenoid tri-

cation would. red.uce the bond. ord.er of the azo linl<age very marked.lyo ÎÌre

isomerization to the p-quinanoid. species (gl:94) worù¿. further reduce

the stability of the cís-forrn. 0n the other hand. the protonated. d.i-

benza-Lamino group of the trication (!!) d.erived. from ,l¡:o,l¡r-bisbenzal-

anrinoazobenzene wou-ld. not be expected. to have a marked. infl-uence on the

azo LirÀ<age. Hence the photoconversion of the 4¡4t-ùibenzala¡ui¡loazober.zene

to the Uenzo[gfciruroline d.erivati-ve occurs in acid.ic soiutions. In this

case also the lowest singlet state (!6) of the photoexcited. cis-conjugate

acia (9¡) i-s the species, probably, involved. in the ring closu:re step.

tr¡ tJre oaee of J-aminoazobenzone, d.issolution in strong suJ.-

phuric aci-d. yields a ùication by the protonation of one of the nitrogens

of the azo linkage and. the an^jno giîoup in the J-position. In the

58.

E

ßz)

r

+ :)

(.9e)

dication (!J) the pr.otonated. a¡ui¡ro grcup ca¡r¡ot d.irectly i¡te:es,t so

strongþ vy:ith the azo group as j¡r lra¡rino- a:rd. 4r4r-*iarni¡roazobenzenes."

6 2+

E

(gz) (re¡

66

The lowest excited. singJet state involved i:i the cyc!ízation step could.

be represented- as (98) in tl::is caseo The non-formation of 1-a¡ni¡robenzo -

[c-l cirurolj¡¡e could. be expected. jf the species involved. jn the cyclizatíonL.J

step of the cis-conjugate acid. of 3-¿yonoaøobenzene i= (gB). The positive

59"

charge in position 6.r and- the protona-bed. and-no group in posr'ciorr J lvould

repel each other a¡id- preV€nlu theii' pncxfu",i{r. llie -I effect of -i;}ie

protonated. anj:ro group 'l¡ill red.uce the developmerft of a negatlve charge

in the 2-position much rnore than i¡r the 6-position and- v¡-ill therefcre

hind.er cyclízaríon at the 2-posj-tiono Accord.ing to the mechanism pr,c-

posed. for the cyclizal;i,on of the cis-conjugate acid. of azobenzene, ring

closure is facilitateC by the d.evelopment of a negative charge ín ;he 2-

or the 6-position.Jl the less hind.ered. position j-n the conjugate acid-

of J-aminoazobenzerre is also the 6-position and the ring cl-osurre takes

place preferentialJJ in thi-s position"

IIT"2 Photochemica.l behavi-our of -) * aninoazobenzene in sulphuric

acic. in the presence of ca.rbonyl cor,rpound-s.

Although lrerninoazobenzene could. not be ind.uced- lo carcLize

plrotocheraically, [-benzalanúnoazobe'nzene lvas forrnd. to cycLíze on irradia-

tion..in 9Ü/" st:Jphuric acid. solutiono The reaction proceed-ed. very slovrly

but smoothly arrcl the cyclizatíon pr:rduct 2-anrinobenzo[g] cirrnoline vras

obtained. in good. yi-e1d.. Althougþ 98% sulphUric acid. was used as the sol-

vent for the reaction, a smaLl pe.ruent.age of 4-benza-l-arnirroazober)zerre

wou1d. be e>çected. to unclergo hyd.rrrlysis and. produce [-aminoaaobenzene

and. berrzald.ehyde. Since the yie1d. of 2-arntrtobenzolg]cj-nno]-ine v¿as unaffec-

ted. it is possible to believe that these d-issociated. reactants recon:bj:red

d.uring the course of irrad.iation to form 4-benzalaminoazobenzene uni.er

the povrerful d.ehyd.rating influence of concentrated. sulphuric acido It

bUo

l,ras of irrterest, therefore, to examine the irrad.iation of 4-amino¿LzQ'

benzene in strong sulphuric acirL in the presence of carborÐrl compoullds

rryàich uncler normal conditions of condensation reacted lrith a-urines to

form the rdated Schiff bases.

The photocyclizatíon of strongly acj-d.ic sofutions of 4-amino-

azobeyLzerÐ in the pl€sence of acetone, cyclopenta¡one, cyclohexaiìone,

benzaìd.ehyd.e and. acetophenone were, iherefore, examinedo 9ff/ó AnaJar

sulphurj-c acid. cou1d. not be employed. as the solvent as a corrsid-erabie

a¡nount of chaming occurt€d. on ai.d:ing the earborSfl compourds " 28ì{

Sulphurj-c acid. was fourid. to be more suitable. lhe cyclizaiíon of 4-aniirro-

azobenzeræ was found. to prc'ceed. in the presence of all the carbonyl

compound-s üs€do The reaction was very slow and. much tar v¡as forir.c:,

probably d.ue to poJ-¡rmeri-zation of carbo4yl ccmpcund. in sulphuric acid-.

the carboryl cornpounds were required. in very consid-erable excess (0"05

n-o1e) to 4-a¡ninoazobenzene (O"U4J. The cyc:-i-zat:on reaction couid. not

be followed. spectrophotometrically d.æ to the masking caused. by the ca,z-

boroyt compound.s and. its pol¡rmers formed. d-uring irrad'iationo In pre-

parative scale experiments, hovrever, the fad.ing in coLour of the þ

aminoazoberLzene in solutionl'¡as obselvedo The efficiency of the carboryl

compound.s Ín effecting the cycl-j-zdtj.on was rougþly in the ord.er

cyclopentunoþ acetone) cyclohexanorÇ benzald.ehyde) acetophenoneo

The cyclized. proC.ucþ 2-amínobenzoLg cirrr¡oline uê.s lsol-ated. in abc¡uU

25-45% yJ.e1d.. tr'ormation of benzid.ine-type prrcd-ucts v'¡ere conceivable as

28N sulphuric acid. was useclo But no other prod.ucts could be isol-ated.

from the intractabl,e tar formed. d.uring the worl<ing up pr'oced'ure.

Olø

The use of benzophenone coul-d, not be employed. as it v¡as

fou¡d to be extremely insolubLe jrr 2&J sulphuric acid.

TII'S Nitroazobenzenes an4AcetvlazoJ:enzenes"

It seemed. of interest to examine other azobenzerLes having

strongly conjugating sr"rbstituents in the 4-position and. solutior¡s of

À-nitro- and A-aceSrlazobenzerres in concentrated su-lphuric acid. t'¿ere

accord.ingly irraC.iated.. Îb.e reaction l,'ras extremeþ slovr v,ri-bh both co¡n-

pound.s but the e>çected. cyeLi..zati-on prod.ucts were obtained" In ttre

cation d.erived. from l¡-n:itroazobenzene a¡rd- þacetylazobenzene the

strongly electron att¡actj-rrg nitro and acetyl groups shouLd. result ino

quinánoid. structures contributing significantly to the resonance h,ybrid.s

(99+>1oo) a-nd (101<-Ðxo2) respectively" The stabitity of the cis

foni of both cations would. therefore be red.uced., arthougþ not to the

same exterrt as in the case of 4-a¡ntnoazobenzene and 4¡4r -d.iarrrinoazo-

benzene.

the lack of any cyclization in the case of 4-d.i¡rethylanino-

azoberwene observed. earlier cou1d. also be explained. by the same argument

as that applied. to the case of 4-aminoaaobenzene.

+ +U

(gg)

<_>

+(roo)

62"

2"t

+-)

+

(101) (¡oz)

the phot ochemical- cyc Ìod-ehyd. ro genat ion o f l-nít rozzobenzene

and. J-acetylazobertzerp in9EÁ svLphuric acid. was found. to be more ra,oj-d.

tharr the correspond.ing reactions of þnitro- arrd. l¡-acetylazobenzeneso

J-Nitrubenzo[9 cinnoline (105) arß. J-acety]benzo[g] ciruroline (tO8) were

obtained. i-n good. yield.. In the cations d.erived. from J-nit'roazobenzene

(1OJ) and. J-acetyLazobenzene (106) there woul-d. appear to be little re-

d.uction in the bond. ord.er of the aza Lirrtkage by the sr:lcstituents, as

there is no di¡ect conjugative interactiono

No 1 -nit robenzofg] cinnollne and 1 -ace tylbenzo [g] cinnoline

could. be detected.. the non-formation of the fatter compound.s could.

neasonably be explained. on the basis of the nechanisrn postulate a51 fo

the cyclizati-.on'of azobenzerleso Aithough eyclízation could. occur to

tine 2- or thc 6-positions, ring closurc to the 6-position is favoured.

due to steric factorso the 6-posÍtion in the conjugate acids (lOÐ anl

(tOe) are consid.erably less sterically hindered tkran their 2-positions.

The deveLo¡xnent of a negative charge in the 6-positj-on in (1O5) and. (106)

I II

63"

1 ro+)

(toz)

NO NO22

66l

+

2t

2t

CH

I to:) çtoo)

( roe)

CTT5 3

hv6þ

+

ll

(roe)

is also much greater than in the 2-positíon, due to tàe -I effect of the

acetyl and. nitro groups jn J-posi-tion. Hence ring closure of J-nil'ro'

anô. J-aeetylazobenzenes occurs preferentially to the 6-position.

lhe structure of )-nitrobenzofe]cir¡noline was confi-rmed- by

its reduction to J-aminobenzct}¿fciruroline. The strrrcture of J-acetyl-

benzo[cl cinnoline was confizmed. by its transformation into the sameL.J

laminobenzoNglcir¡nofine by the Beclgnan rearr"angement of its oxi¡re (109)

64.

..:ìd. subseguent hyd.rolysis of the J-acetylaminobenzofg]cinnoline ( 1 10)

so formed

l+

( rog) (tto¡

65"

E xl:e r j-¡ne n-b a]-

Preparation of the azo compor-rrrd.s

/a-B e nz a 1 arni no e z ob e :t zene "

À solution of 4-arnínoazaTter'zene (5.0 g) in boiling etlianoi

uas mjxed. with an equj-molar quantity (2"7 g) of benzaLd.ehycle (2,7 g) "

After J0 ninutes the crystailine pncd.uct was collected.o RecrystaiÌLzzLion

frortbenzene/ethartof (t:t) gave l¡-benzala¡r.inoezoberwene as shirrj-ng red.-

broy,n plates m.p. ßzo (rLt,. r73 'r5o"5o).

l+. l+r -B j-sb enzal arn-i.n o a zob enzerte "

4¡4r -Ðisacetylaminoazabenzene rvas prepared according to the

method. of SanturrÍ and. coworkersT4 (tr, 6ür7i, yie:rô.) ¡y tr,," oxidation of

þarninoacetanilid.e with sod.ium perborate a¡rd. boric acid. in glacial acetic

acid" ilytlrolysis r¡¡âs effected. with methanolic hyd.rochloric acid. to give

4r4!-dianrin oazobenzene m.po í4úo (Lít" ,75 zqjo) in al-most quantitative

yield.. This d.ian:inoazober.zene (5 "2 g) in boiling etha¡ol was trea-r,ed.

with an eqr.ürnolar quantity (+.+ e) of berualdehyde. Recrystal'Lizati.on

of the product (8.e g) frrom benzene/etYøncf (1:1) gave ,l¡rJ¡¡-bisbenzal-

a¡ninoazob er,zene as brrcrn¡n plates m.p, 2OOo (tit. ,76 ,gAo) (For.rnd.: C, BO.+;

H2 5.2; N, 1l+"2. Calc. for cr{lrd*t c, 80.4; H2 5"2; N, 14")'l;).

4-acetylazobenzene.

A mixturre of l+-aminoacetophenone (6.76 g), nitrosobenzene

66"

(t.+ ù aa1 glaciai acetic acid (JO mI) v,,as heated. at 600 for three

hourso The prcd,uct ...¡as chrorøtographed. on al¡nirra using l-ight petroleum

(b"p. 4!-7Oo) as eluant a::d. the firs'c d.eep red. frac'¡ions v¿ere collected.

and evaporated. (yield. 6.2 g)o Recrystallization from ethanol geve 4-

aeetylazobenzer,e as shining red. need.lesr ilop. 115() (lit " r77 ,15o).

4-Nitroazobenzene "

A rnixture of ¡-r::itroarÉline (6,1 ù, nitrosobenzere (¡"+ g)

and. gJacial acetic acid- (JO ml) vras heatecl on a r¡¿ater-bath for 6 hor,,r's,

then set asid.e for J dayso The prod.uc'c vras precipitated. by d.iJuting

with v¿ater, extracteC. vl'ith light pe'crolervn, the solvent evaporatec anå

the residue chrornatographed. on a1u:r¡ina usj-ng hexa¡e as eluarrt. The first

red. fractlon I'ras coll-ected- a-nd evaporateC.o Recrystall-izatian of the

resid.ue (+.e *¡ from ethanol gave !-nLtroazobenzene as lighi red. needles

m"p" 1J5o (tit" ,7u ,3,o-r55o).

J-Nitroazolcenzene "

A mixture of rrrnitroaniline (6.7 e) nitrosobeîzerLe (5"+ g) and

gJaciat aceti-c acia (BO nù) was heated. on a water*bath at 650 lor 2 hours

and. then set asid.e for 48 hours. the product vês extracted vrith l-igþt

petroleum after d.ilution of the m:i-xture 'lvith ræter. ?he solvent was

e\raporated. ard. the residue chromEttographed. on alunrina using 'oenzerre/

Ii.ght petrcJ'errm (t: t). The first ol:ang,e-red. fractiolL vês evapo:'ated. an1

the residue (8"5 g) reczysiall-izec1 fro¡r etha:roIo J-l{iiroazoì:enzelte ,.¡/as

obtained. as red. prisrnsr D.p. 960 (r:-t "r7' ,5.5-96o).

Þ/"

3<\mj-ncazcbenzene "

J-Nitroazobenzene (5"0 g) v,as ad.ded. to an ethanor ic soluticn

of sod.ium sulphid.e (ZE g) an.J. the rn:j-xture refluxecl. for J hourso lhe

alcohol was then eva,oorated and. tlie soliå (+ g) collected. and. recrys-

tal.}ized. from JJ/o methanoi" J-4.nj-noazobenzene was obtained. as orange-

yerto'vr need.les¡ n"po 680 (tit" r9o nro) (Fo..uid: a,r 73.Ji Hr 5.6; N, 21"oo

Caf-c. for C., FnN¡ Q, 73'1i Ht 5.7; N, 21"fu). ,

J-Aceiylazobenzetx¡ o

A miy.ture of J-aminoacetophenone (6.7 S), nitrosobenzene (5"4

and. glacÍal acetj-c acia (50 nJ-) vras heate ð, at 5O-5Oo for trvo hours a¡d-

then set asid.e for J6 hoursn The pncduct '¡'¡as precipitated. vrith vt'u:"z:,

extracted. vrith ligþt petroleum and. the solvent evaporated." The residue

vras chromatographed. on alumina using, light petroleurn/berlzetLe (t:f ) as

eluanto ÎÌre first oraJrge-red. fraction was collected. and. evaporateC.o

Rec:rystallization of the residue from ethanol gave J-acetylazobenzere as

flai lemon need.les¡ h.po 8Bo (tit.r81 B8-9oo¡ (Found.: cr 75"O; H r 5.5;

N, 12.2o Calco for C.,UH., rNrOzW5"O; H, 5"4; N, 12.5%).

Phot ocÌremic al Cr,rclizat icns,.

A solution of Þbenzai-a¡ninoazoþenzerp (t.O g) b.9q!, ê.naIaz'

sulphurj-c acid. (120 nü-) 1'¡as irr"adiated. J-n a !yrÈ:{ reactorlri'uh a inercury-

quarla lamp. The reaction appeared. to be compJ-ete after 92 hours, there

being no further change in the ultravi<¡let spectrr-rm of the solutj.on"

s)

68"

Dr:ring the reaction sulphur d-ioxid-e appeared. to be evol"',¡eô (po'cassrure

ch::omate paper grad.ually turned. green) o lhe ntixture l'ras pour€d. into

ice-cold. v¡ater and. v¡as extracteC. rrith benzene to remove be:rzald.ehyd-e

(id-eniified. as the .ùinitrol:Ì:.enylhyd.razone). the aqueous aciåic sol-u;ion

rras basified. r¡ith sod-j-'*n hyarnxid-e and. repeatedly extrac-r,ed- '',zith be:-rzene"

Evaporation of the benzene gal.¡e a dark re¡;iclue (O"67 g, 9T/; crud.e yieid.)

'r¡,'hich was recrystahj-zed. froln ethar:ol . The resultítg 2-asu-no'oenzoiS)'

cirrrioline v¡as obtained. as shining yello';r needl-es¡ iloP. 2+7o (Iít"t82

z+-zl*5") (Found.: cr 73.9i He 4.6; N, 21o2o Calco for C.eHgNJ: C, JJ"B;

H, 4.6; N, 21.5?á) o I',6s solutions in ethanol, d.ilute sulphurio acLù,

anrl acetic acid. shoived. green, greeirish-ye1lolv, and. yellow fluoresce-irce

respectively. The ultraviolet slrectrum in 2ã[ suJ"phuric acid v¿as c]osely

sjmilar 'r,o. that of benzo ¡3¡ cinnoline in 2oN sulphuric acid" the aceiyl

d.er-i-vatives (preparerl by refluxi:rg with acetic arrhyd.rid.e in glaciai

acetic acid.) crysta}lized. from ethanol in pale ye1low nee<lles¡ lïro,oe 2l+Oo

1f:-t.!2 ?59-zl*oo)o The sa]-icylal,åehyd.e Sch-iff base crystallizecL frc¡;i

eiharrol as shining pale yelJ-oui pLates¡ ffi,p. 1E6o (Four:c}: C2 Jir'zi

H, 4.5; N, th.O. argnt¡\O requires C, 76"3; Ht 4"J; N, l'l+"Úi'ù o Diazo-

tLzatíon of 2-aminobenzoßÌJ cinnoLine, and- treatment 'r'r'ith potassii¡n iodid.et

gzve 2-íoaobenzolg] cinnoline. This separated. from ethanol as yellovr

needfesr r.po and. nrixed. m.p. z17o (tit. r'9 ,r7"5-218o)"

69"

l.*Am'i z benzene lrìa) fha n¡a of carbo ^-_n¡r r_aÄ c

A solution of 1+-arninoaaobenzene (0.! g) in 28{ sulphuric acid

(fAO mf) was nr-ixeù v¡ith the folloving carbonyl cornpouncì.s (O"O¡ lj) errl

was irrad.iated. for the ird.icated. ti:ne in a Pyrex reactor with a ÍÌerciif-Jr-

quat'uz Iamp. Ifnen the reaction appeared viztually complete (by o'bser'r-

ing tre fad.ing i¡r coLour of [-aminoazobenzene) 'uhe reaction nüxtur¿ r'ras

d.il-uted. and. the tarry material v¡as filtered. off. the aqueous acid.ic

solution v¿as extracted. rrrrlth benzene to rernove al-I the carÌ.lor¡r1 compound.s

and. basified. with sod.ium hyd-roxid.e" Repeated extractioir v¡ith ber^zene,

evaporation of the solvent and. recrystallization of the resid.ue fro¡n

aque ous etha¡rol aff o rtled. 2-aminobe nzof c1 cinnol-ine o

In the presence of Acetoneo

A solution of [-amínoazo'oenzene (0.5 g) and. aceton" (2"9 g)

in 2&-{ sulphuric aci-d. was irrad.iated. for'l'10 hours in a Pyrex reacto¡'"

Ilre reaction mixture was worked-up as d.escríbed. above anC. 2-a¡rinol¿enzo-

F]cj.nnotine (0.2 g, Wl yiefd.) was obtained. as greenish-yeIl¡¡w need.Ies,

m.po 2470 âIone or mixed vrith a previously prepared. sampleo

In the presence of c.yclopeiltancne.

Ja-Äminoazobenzene (0.5 g) a,rd. cyclöpentanone (+.2 g¡ in 2&'[

sul-phuric acid. was irrad.iated. for 96 hours, Irom the reaction rni-rJirre

2-¿¡ainobenzþf clcinnoline (O.ZZ g, )+5T'" yield.) v¡as isolated. as above"

70"

In the presence of cvcl-ohexanoncn

A *ixtuæ of 4-a,ninoazoltenzene (0.5 g) ard. cyclohe:<anone

(+.g g) in 2&'[ s.*lphuríc acid. was i-:rrad.iated. for 156 hourso 0n being

wor.ked.-up the reaction mj;<tu¡e gave 2-aminobenzofclcinrroline (O.tg g,

Jff¡ír) m.p. and. mjxed. rr"p" fu-fo o

In the presence of benzald-ehvd.e.

A solution of l+-aminoazobenzene (0.5 g) a'¿ benzal¿ehy¿e

$.1 ù in 28$ sulphuz.ic acid. rvas irrad.iated. for 200 ho-urs" 2-Amino-

benzolclcinnoli¡re (O.tB g, 36% yield.) was isolated. as d.escribed' above.

In the presence of acetrtphenone"

,l¡-J^rninoazobenzene (0"5 e) and. acetophenone (6 e) in 2&i

sulplruric acid were irrad.iated. for 256 i6otttso 0n being rvorked-up the

reaction mixture gave 2-arninobenzot!] cinnoline (0.1 g, 2Úl(' yield') ¡ H.Po

2\70 "

L-lrû -8is b enza]. anrino azobenzerte .

A sol-ution of l-r]¡r-bis'rrenzalaminoazobenzene (t,O g) tn )81o

.Anal-ar sulphuric acid. (120 mI) was irraôiated. in a nerr;ury }ænp react'pr

fot 216 hours, then poured. into ice-,,vater and. extracted. with benzene (to

renove benzald.chyd.c) o lhe aoid-j-o eolution was then neut-ra..ì ì zad vnih

sod.iwn hyd.roxid.e and. repeatedJ.y ex'uracied. r,rj-th benzene rintil the extract

v¡as colourlesso Evaporation of the benzene solu-"ioi1 gave a d'a:'k residue

7i"

(0"+6 g, B}"iù recrysiallization of .vÌrich, from etha:rc)-, gave 2r9-

d.ia¡n-inobenzo[glcinno]-ine as ,oal-e yelJ-ovr needles, vrhich decornposed. .;,':--!irout

melting at J16o (ritor8j u"r. ll5") (!'ound.: c, 68.6; H, )+"8; i,i, 26"1t-,

Calc. for C.,ffO\r S,r 68"6; F.r 4"7ì N,26.7/o)" lhe ultravioLet abscr1':-

tion spectmm in 22N suJ-phu::ic acj-C rn¡as closely si-:mlar to those giv:n

by benzo[c"lcinno]ine and. by 2-a¡ninobenzcfclciirnoline in 22'{ sulphult'i-c'L'--¡-l-J=-

acid. ihe n.m.r. siæct:'uirr l.¡as d.eterrnined in d.j-n:ethyl suJ.,oho:cid.e .,ri'ch

a Varian DP60 spectrophotometer using tetrarneì;hylsj-lane as intcznal

reference" It showed. a broad- single'b at 3.67 (tour pirctons) assigned. to

tzo arn-lno groups at the 2- and. !-positior'Is, a quariet (par/ciy masked.

by the singlet) at 2.7 (trvo protons) asslgned. tc t,,¿o protons at J- ¿¡¿

8-positions, a singlet at 2"67 (two protons) asslgned to protons a'l'j-

a.nd. 1o-positions and. a d.oublet at 1.8,1+ (two protons) assigned- to .orotorrs

at the Þ and. þpositions.

Acetylation was effected- by refhu<ing vrith acetíe anhyd-ride

ard glacial acetj.c acid.o Recrystallization of the product flu,ri aqueous

e th anol gav e 2 r)-bisace tar.id.obe nzo 19 ciruroline as f ine lemon-yelJow

needles¡ üop. ¡460 (founaz C, 6J"6; H, J"2; N, 18.2" Ct6HlhBhOìunro

requires Ar 63J*i Hj 5.0; N, 18.51;)"

2 r9-Díaninobenzo[g] cimoline vras also oi¡tained. in comparaì:le

yield foll,o,wing irrad.iation of the bisbenzalaminoazobenzene, in !8;Z suJ.phuric

acJ-d., ln sunllgþt for 25 d"a,ys.

L¡ I'I i.i roa z obcnzer:e "

A solution of [-nitroazo'Þenzene (t.O g) tn 9{lí Analar su}1ùruric

72"

acid. (120 mI) tïas irrad-j-ated in the mercury lam.c reacto:'" Ti:e reaction

r,vas virtually cornplete in J10 hours as there I'¡as no fuC;her cÌrarrge in

the ultraviclet spectrurn" The rnjxtr¡re v/as then òiluted. r'itir ice,

neutralized- r,r'ith sod.ium try<J.roxid.e, arid. extracted. 'lrith benzene" E'/a-

,oor.ation of the benzene solrrtion gave a dark brrcr',r'r resicue v,liich "vas

¿issolvefl in concentrated. hyd-ruchloz'ic acid" Dil-u-ûion of t.ire strongiy

acid.io solution gave a pale yellou precipitate vrhich r'¡¿s collected. ( a.J gt

JÕ11" yiel.ð.) and. recrystallized from ethanolo 2-Nitro-benzoE:fciru:oline

v¡as obtained. as pale yellovr plates¡ ffi.p" z690 (:rit"r7J ,69-27o")

(Fonnd: C, 64"0; H, 3.3i N, 'i8"J, Calc" for c., ]iftorz C, 64"oi H, 3"',; N,

18"6Y") o The same prod.uct r,¡¿s orotained. foilorving irrad.iation of À--

nitroazobefizane, ín 98% sulphuric aciC. for 29 d.qys. Reduction oÎ 2-

nltrobenzofclcirueofine vrith sod.ium sulphid.e i-n ethanol gave 2-a,¡nino-L-J

benzof cl ciruroline r fl.p. and. mixed. n"po 2460,L.J

h=\cetvlazobenzene.

A solution of l¡-acetylazoberlzene (1.0 d ín 9U/" Ànalar sui.-

phuric acLd. (120 r¡f) was j-rrad-iated. in the meIEuIy lamp reactor. The

reaction was complete in 240 hours as j¡rd.j-cated. by the ultravj-olet spec-

trum" The rnixture was then d.ituted. vrith ice, neutralized, with sod.ium

hy.d.roxid.e, and- extracted. r'rith benzene. nvaporation of ihe benzene

solution gave a d.ark bn¡.¡,¡n residue (0.6: g, 66ll) vu'iri-cn r'¡as ci'¡ro¡r¡atogria.piredr

on alumina using benzene as eluant. The light yellorv frac.;ions rvere

evaporated and- the residue recrystalLized. fro¡n ethanol. 2-!,cetyLbenza-

fc]cirurol-i.ne was obtained. as yellow needfes¡ ilop. 15úo (Forlnrl; Ç, 75.8i

73"

H¡ 4"8; N, 12.2o Ct4HtONzO requlres, Cr 75.7; H, à.5; Ni 12"6%).

@.A solution of J-a:rúrtoaza-oenzene (1.0 g) in )Ûi/" sulphl:ric acid

(tZO mf) vras i-rrad.iated. in the mercury lamp reactor w¡til the reac-bion

vras complete (1OB ho'.rrs). 'Ihe r¡ijxture \.¿s then diluted. rzith ice, basi-

fied. vrith sod.ium hyd.roxid.e and. repeated.Iy er:tracte,l vrith benzene" Eva-

poration of the loenzene solution gave a d-ark brsvn-r resid.ue (0.4É go +7iù.

IhÍs lvas chromatographed. on alurnina usÍng benzene as eluant, and. the reC.-

yellow fractions were collectecl arrd evapo::ated." Recrystalliza-uíon of the

residue from benzene gave J-aminooe"^lgcinnoline as red-bro'¿,rn ne<,dles

m,po '! 63o (::it" o7J ,ez-tqo)o Reflu:',ing vrith acetic arrhydrj-de in glacia-i

acetic aci.d. gave J-acetamiaobenzolg]cinnoliner nop. 297o (Iít"r73 ,96-

zg7o) (For:nd.: c,7o.9i H, +.7i N, 18,1o cal-c" for CTUHTINJO, ct 7c"9i

H, 4.6; N, 17.91)o J-AminobenzoßJcirrnoiine vras al-so obt¿rined. jn the same

yield- follotving irrad'iation of 3-arinoazobenzene, in sulpìruric acid', in

sun-liglrt, for 10 d.qys.

J-AminobenzoF] cinnol-ine vras likevrise obtalned. ( in sirnilar

yield.) utren J-benzalaminoazobertze-rte (t.O g isolated. as a red-bro"tn oiJ)

in 9ü/,1Sulphurj,c acid. (120 mJ.) was irrad.iated in the mercuÐ/ Iamp reactor

fot 96 hours. The pznduct had. m"po and rnlxed. m.p. 1530 , and. the acetyl

d.erivative had. m.p. and. rn-rxed. mopo 29-lt "

71t,"

1-!{itroazobenzen

A solution of J-niiroazobenzene (t.O g) in 9tl Ana1ar s-,:1-

ph,"uic acid. (120 m1) l'.'as irrad.iated in the mercu-ry lamp reac+,or'îor ZJO

hours, then d.iluted. vrith ice and. the resuJ-ting preci,oitate collected.

the filtrate v'ras basifieC. anL extracted. r'rith benzene¡ and. the ex'r,ract

evapoz'ated.. The resulting resj-due r,'¡as cosibi-ned. r'rith the a-Þove precicì-tate

and. d.issolved. in concentraieC hyd.rochloric acicì- (10 nr"i)o The soiution

v¡as filtered., ancl the filtrate d-iluted.. the res,-¡]-iing yello',v solid

(0"99 g, 9ú/; yield) vË.s recrystallized. fro¡n ethanol/h"nu.n (l:t) , )-

Nj-trobenzofclcinnoU¡e was obtained. as shir¡ing yeJ_lovr piates¡ fl.p. 2r9oL-J

(tit. u73 z5e-259o) (nouna: cr 6L.5; rI, J.o; N, 1B"Do carc" for c,.[-¡trorcr 64"Oj H, 5.1; N, 18"7/ù" The saÍre prod.uct v¡as obtained. in sinúl¿ir

yíeld. follovri-ng irrad.iation of l-nLtroazobenzene in sulphuric acie in

sunJ.ight for 26 d.ays.

Red.uction of J-nitrobenzc[çJ cinr¡o].ine was effected. by hea'cing

wi',,h alcoholic sod.ium sulphid.e on the v¡ater-bath for 2 hourso The resul--

ting solution v¡as d.iluted. with vrater, extracted. vl"ith benzerr.e anrl. ihe ber.-

zene extract evaporated. The resicìLie lvas recrystallized, from benzene

to yield. J-aminobenzo[g]cimo]-ine as red.-bro'¡,rn needles, mopc 16Jo r,oi

d.epressed. by ad.nr:ixture 'urith a specirnen prepared. by photoclremical cyclo-

d.eLgrd.rogenat ion of J-amin oascib errzerte .

c¿i azobenzene

A solution of J-acetyLazo'penzene (t.O g) in 9$4 Analar sul-

7i.

phuric acid. (120 m1) v¡as irrad.iated. jJ} ttle mercury.Ian,p reactor. the

reec-i;ion appeared. to be complete after 108 hours, no fuither change i¡

the ultraviolet spectrum being obsezr/ed. the mlxturs v¡a's then ùj-luted'

lvith ice, basified., and. then repeateòLy extracted- v¿j-th benzene' Eva-

poration of the solvent gave a bror"rn residue (0.7 g, l1lå yLeLd') rvhich "ras

chmmatographed. on aluni'j:ra using benzene as eluant. The fi¡'st yellolz

fraction v¡as col-Lected, evaporated. and' the residue recrystallizea -f;:ort

ethanol. 3-ÃcetvLbenzofc] cirLroiine v¡as obtainecL as lemon-yellolv nee'fles

m"p" 21oo (rounaz c2 75.7i -Ã, \.6; N' 12"6' "1,\-n1oNrO

re9uires C ' 65'7;

H, l+"6i N, 12"6"/;). The same product v¡as also obta-ined in -l1lô yieL1 iollov¿-

i-ng irrad.iation of J-acetyLazcbenzene in srrlphuric acid' in su::-light for

1.[ d.4ys.

1-Benzo fc] cir¡nolinyl me'chyI. ketoxjme'

Hyclroxylarnine (from hydro>ryIami¡re hyC.rochlorid.e, O.J g) r:'as

ad.d.ed. to a clear solution of J-acetylbenzofg]ciruroline (o.l g) in 95%

etiranoland.thernixtuzewasl¡¿alTned.onthevrater.bathforafevr¡ninuteso

34en'¿ofcl-cinnolin:¡1 methvl- ketoxilqe (O'lt g) separated f torn benzerte/

etharrol as ligþt yeSJow prisms, m.p. 2!Bo (For:nd': Cr 70"6; H, l+'8; N, i7'7"

at'nl.,NrO reauires, C, 7C.9; flr'["6; N , 17"71;)'

Becknann Rea LU

Phosphoruspentachlorid.e(0.¡e)r'¡asad.d'ed.toasuspens]-cj}

of the above oxi¡ne (o.z ù in arhyd-rous benzene (to mr) and- the m'ixture

lO"

l'¡aflned. on a water-bath for 2 minuteso The resulting oz'ange-yellorv

solution 1¡üas evaporated. and. the resj-ciue warmed. r'rith r'¡ater for 10 run-

utes. the inscluble material was collected. (O.lf g); recrystalliaatioir

from acetÍc acid. ga.ve 3-acetylaminobenzof$ cinr¡oIine as lemon-yelloly

need.les¡ fr"po and. rnixeC m.p" 2g7o" The infz'arecl strrctrwn ï/as id.entical

l'rith that of an authentic sarnp]-eo Hyd-rolysis t',rith d.il-ute hyclrocirlorjc

acid. gave J-arninobenzo[c-] cinnoline¡ roop. and. nbied. rn.p. 1620.

ci'-r1!?ilrlR I\r

Photochernical Prope;'ties of

A. zob enzene-Z4 a fc oxylic ac id's o

77.

Photochernical P rties of Âzob ene-2 -n¡ -n1r I -lt cid.s7lÍì Tì ê ?.

The phot ccataiyse'i cyclod.ehyd.ro gerrat ion reacl;iorL af azo-

benzene and severaL of its d.erivatives has been investigated. in s-i;i'ongiy

aciòic solutions and. Ít has been shovl-n that rnany sr:l¡stituted. azobenzeîí.i

on irrad.iation f ozn the related. benzof9 cinno]-ines, someij.:nes lzi-¿h e jec-

tion of suj¡stituents ff om the position of cycLization; and. irr many

ins-Lances benzid-j-ne-type proc.ucts also have been isol-ai;ed.o 26-10'32

Substituents have been found. 'r,o exei-b eL profound- effect on tì'ie rate of

cyclization. Strongly ccnjr.rgating subs'cituents j:i the ,l¡-positi-on in-

hibits cycLization, and. no cyclizatj.on v¡as obserred v¡hen u.r, ori.rorL9).o z(

d.imethylarnino+7 or phe4ylarni-noJ' group r.ras present j¡. the {--posi-cio::

of azobenzeyLe.

fn the mechanism postulated by Bad.ger, Drevler and. l'.rrr"3tr

for the photochemical cycJ-od-ehyd.ncgenation of azobenzenes (d.etail-ed. in

Scheme II) a short-Iived. photoexcited. state of the cis-conjugate acid.

of azobenzene was envisaged. as tùre species j¡¡r¡olved. in the ring closure

step" The effect of substi-tuents and. acid.ity of the med.ium on the raie

of cycLization and. cluantum yield. were stud.ied." fiith the three azobenzerres

examined. there vtas no direct correlation betv¡een the quantum yield.s or.'

cycLízation zeaction and. Ha;runett substituent constants" It 'lvas sugges-z.l

tedJ' that a satisfactory expl-anation of the effeci of substituents on

the quantum yield, nrigbt be possible i-f the ratiob of the two tautoneric

forms of the cis-conjugate acid.s of [-chloroazobenzene (66 and. 67r;t, = Cl)

and. þ-methyJ-azobenzene (66 an . 6-1, E - ì,.e) present in sulphuric acj.d.

78.

solution vlere knovrne

An exalrination of the properties of azobenzene-z-earboxylic

acid (111, R = Rr = H) and- of its A-chloro-(1f i, RR = H, R = Ci), L,t-

ciil-o:.o- (tll , R = H, R! * c1), 4-methyl- (111, Rr = H, R = 11e) e and' L,J-

methyþ (tlt, R = H, Rs = l,{e) derivatives has been underbaken in,orepara-

tion for further possible photokJ-netic stud.ies, designed. to suppleneu-l

Þ

H

q

B.+

(ttt¡ (ra)

quantum yield. data for the photochernical cyclod.ehyCrogenation reacticils

of azobenzerLe, þchloroazobenzene, ard /¡-methylazobenzene" These corn-

pound,s .¡¡ere chosen because it v¡as thougþt that the carboxyl group in the

2-position through hyd.rogen bond.ing -'¡¿orrld. reLry the ad.d.ition of the p:rcton

to the c-nitrogen giving only one conjugate acia (112) in strongþ acid-ic

solutions

This chapter d.escrihes stud.ies of the irrad.iation of azobenzene-

2-carbo{f1i.c acicl a¡d. 1ts þchloro-¡ 4e -chÌoru-r 4-riieil-ryi-, al:d 4Î-rncthyl-

d.erj-vatj-ves in !8/, sulphuric acid. anrl j¡r benzene solutj-onso A conpara-

tive stud.y of rates of cycLLzation ¡n 9Atá srrlphuric aci-d. j-s aJ-so i.escribed.

79"

the availability of pure samples of the cis-èoners of tìre azo

compounds j¡r ad.d.ition to the normal trans-isomers and. of the correspon'C.ing

cycli-zed. prrrd.ucts, is an essential reo-uirement for the previously erc-

z-1

ployed. method/ fo" d.eterrcination of quantum yield.s. Accordi:rgly atrrernpts

have been mad.e to obtain the azobenzene-Z-carùoxylic acids in the irs

for,rs and. the benzol9 cirrro]-ine-À--carboiylic acid.s have been prepareC. by

photochemical- cyclod.ehyd-rogenation of the sr:bstituted. a-obenzene-Z-eat-

boxyli-c acj-d.sn

TV.1 Trradiation of azobenzene-2-caT'Ðoxvli.c acid. i-rr 981ä sul--::,':'ic

^^a ^¿LL;¿LL.

ilr.ar.on of l¡-chroro- (111, R.¡ = H, R = cr)e J¡'-chtorrc-

(llt, R = H, Rr =.cl-), À--methyl- (111, Rs = He R = Me), and. À.r-methyl-

(llt, R e H, Rt r Ife) d.erivatives of azobeT)zene-2-carbo4ylic acj-ci =n 9Vo

sulphuric acid resulted. in tkle f oz:nation of the correspond.ing benzo[E] -

cÍruroline-,1¡-carboxylic acids (ltÐ i:r good. yield.s (lZ%, 6A/", 7'V/", ana 6J/"

r"espectively). ,[r -Methylazobenzene-2-carboxy]io acid. gave rise to a very

smal-I a.rrount (tess binan 1/i,) of an r¡rrid.entified. d.ecarboxylated. cyclized

prod.uct, presr.:unbly 2-methylbenzop].cirrnoline (lll^., R = H¡ R.r = Ue) bui:

d.ecarboxylation d.id. not appear to take place d.uring cycl-ization of the

remaining three azo compowrdso

As j¡ the case of the photochemlcal cyclocleiryùrugcnatioirs of

other monoazo compourrds in 9g'r:¿ sulphuric acid', no red.uctíon/-oenzid-i::e-

.-,..j'.. : r... ,_ ,-. -' ,:.íj -lt..".:.:: ,.,'..'.', '--'-: ', r'1.:,i,l. \..:: r.r . i- .,

80.

R

(ttt) (tt:) ( 1 1À.)

this respect, all the monoazo coinllouncls so far exa¡rined sho\'.' con'r;raistilg

properties to the bi-sazo cornl:ound.s "30'32'17

It has alreaql been fourrA29 that azob enzene-Z-carboxylic aciC.

(l,tt, R = Rr = H) , on beir,g irradiated in 22N sulphuric acid. forms a

raixture of benzofg cinnol-ine-þca::bo>y1ic acid. (l'ii, R e Rt = H) (iy"l.

yielC), benzoçElcinnoline (lt\, R = Rt = H (616 yíe¡d), benzid.ine-5-

carbo>rylic aciC ß511 yteLd.) , and- benzid-j-ne (6fi yiel:ù) , and. it therefore

seemed. of jnterest to irracliate thís compound. in 98% su1'pltu:'ic aciC.

Und.er these concl.itions, benzolgcinr¡o1ine-l¡-carbo:ry1ic acicr a¡rd. benzo-

fc'l cinrrolirre were formed. in þ% and, 24% yielcls respectiveiy, but not- I

re d.uct icn/b enz idine- Tea frangeni ent prod.uc ts coul d. be d.e t e ctecl.

l¡Iith 2-substituied. azobenzenes , cycl)-zation ca¡ occur at the

6-position to give 4-substi.tuted benzopJck¡nol-fu;e. CyclizaLiu¡t c¿¡l,r ül-ùy

occur at the 2-.position if the substituent is ejected' Previous r'.'ork

has shol,1r'¡ that substiiue:its lj-lce a ine-ul,yl-, chloro-, iod*-, or caiooxy

Õls

group are ejected to a ljmitecì exient d.uring cycl-LzeNion" Despi';e the

fac-t that a carboxJ¡' group is usuall¡r regard.ecì as a be-,,ter leavirrg È,roup

tlra:r a rnethyl or a cLrloro group, the irracLiation of azobenT'ene-2'

ccLrbo4yJ-ic acid.s ir\ 951'6 sulphuric a-ciö. yieJ-ded. the related, benzofsf -

cimolirre-ja-carboxylj-c acids as tiie major or oniy procluct. lhe suggestion

has been mad.e that the re-l.atively snall extent to vrhich azobe-¡zene-2-

carbo4ylic acid wrdergoes photochernical c¡rçiization v'¡ith loss of the:

carboxy grcupp corrpared., for exiurç}e, r,ri'e,h, the exieni to v¿hich tlie ne-lhyi

substituent is ejected. fTorr\ z-m.eth¡rlazoberlzene t mII be C.ue to h¡'drsgst

boncì.ing betv,'een the carboxy group and the aao linkagen the present irork

prornpted. us to exar¡line this suggestion rnore criticaily'

the carÈoxy group o f 4,' -d.imethylanr-ino azob enzeîte -2-carbo:cy1-ic

acid. (111, R = H2 Rr * N(it,le)2) ancì ihat of the corresponclir'g \t -d-ichlo¡o-

ethylamino compound (11'!¡ R = H, Rt = N(Gf2-tHzcl)z) has in each case

been shor'¡n8+'85 to be internafry hJ'crtgen boirded to the near.er azo

nitrogen atom (stmcture'tf i)" lvloreover there is evíd-ence tkrat the pruton

in the fi.rst conjugate acj-d.s of these cornpor:rrds is attached preferentially

to tb.e azo-nitrogen atom adjacent to the ring bearing the carbo>y group,

althougþ otl:er types of substituents in the 2-posltion of si¡¡rilar ir.ol-e-

cules hind.er protonation at tr,e azo linkageoS5 th""" observations suggest

that the carbo4y group relays acld.j-tion of the proton to the azo-ni-trogen

ancL the conjugate acid. ( 112) rnay a,l-so be intemal-J-y hyd.rrcgen J¡oncLed."

82"

R

Rr l-l

+H+-----7

!

(111) (112)

Althougþ it has not been pobsible to sholv r'.&rich a:+.ni+.r'oge:r

aiom jr¡ the currentiy e:canúned. azobenzene-Z-carbo4ylic aci.d. is prefer-

en'cial-Ly pnrtonated., it seem^s liicel-,v th¿rt the conjugate acid.s may e:<ist

in the d.epicted. forrns (112) in sulphuric aci.d-. If so, hyclrogen boridi:'g

cou-l-d. be retained. duri:rg trans ->

cis isornerj-zation ancl this v,,ould be

erpectecl to prevent photochemical ri-ng-cl-osure at the 2-position and.

corlseo.uent ejection of the carùoxy groupo IntramolecuLar hyd.rogen bond.-

ing betvree¡r the carboxy grrcup ancl a pnoton attached. to tlie a-ltertative

azo.nitrogen atom, on the other hand., would. be e>qpected. to hind.er

trans --SE iso¡rerization a¡:d. cyclizationo

îhe i¡frared. s1æctra of the azobenzene-2-carbo:ryIic acj-d.s in

carbon tetrachlorj-d.e solutions have nov¡ been exa¡nlned, a:d. the resul-ts

cor¡fiim tìr-t the neutra-l for:ns of 'LÌrese moJ.ecul-es are intr¿r¡nolecularly

hyd.rcgen borid.edo Measurenents l'¡ere o*¿J at d.ifferer:t concentratiot'rs.-7),(5 x lO2 ¡1 and. 5 x 1o-.+ fi in ceils of cornpensatirrg path-J.engths ( 1 cnr

anô 10 .r l""n""tively). '-rr'"

1or,¿ sol-ubjJ-ities of the compowd.s d.id. not* Th" author is grateful to Dr. G.E. Lewis for running the i¡Érared. spectra

20'iR

J'!

i\i4oc;

l,i

IT60T

j,l

cB0î

87.

7500 5300 t10a )cn.

fnfrared. spect::um of ezobenzene-z-carborylic acid. in

carbon tetrachloride at concentrations 5.7x10-lU (1 cm. ceils )

-q'r ( l0 cm. ceils)

"/"

and 5.7x10

FÍguro 1.

84.'

pen:rit exarni¡:.¿ition of tne spectra at higþer concet:tr'¿"úioi-¡s"

In the spectr.um of azo'oenzerß-2-earjbor¡rlic aci-cl the oruy

sig:iifican'i; absorption in tne 5 ¡ region '!'/as a broad, 'pancL rvith a rJiåxilîuirl

near JO6O cro-1 (bonCed. CIi); and. no marlced change j¡r ti-e spectrrirn or:ci:r'recr-

with d.iluiion. The single cuïv'e (ligure i) accord.ingly re¡.,,2'esents -ihe

me¿rsurenents obtajrred- at both concentra.tions' Tkie spectra of tÌ:-e J'-

chloro- ¡ 4r -c|rlor.c, - , )rnetLryl-, anå !"t -rnethyl-azobenzene-2-c?.TT)clrlyì-'' c

acid-s were all very similar to that of azoTtenzene-2'carboxylic acj-t,

ancl these likevrise shorvecL no signi;f ica.rrb a-lteration with d-j-l-utio;-l"

The spectrurn of azobenzene-J-carbo)ry1ic acicl (Figure 2) in

v¡hichintramolecularhyd.rogenbond.ingisnotexpecteclshovrec]trr'od'is-

tir-c'c bands in the 3 y region, the respective maxima occu-r'ring neai.4 -4jgj¡ c5i¡ (ur,bond.ed OH) ancl JO6O cnr-¡ (bonded. OH)" As dilution c¿tused

the bancL at 3530 crn-1 to increase in in'censity, l'Àile the intensÍty of

ihe lcand. at 506O cm-l decreased c;uite ir,arkedly, it was .clear that -;liis

coinpound .y¿.s intemolecularly hyd.rrcgen bonded. Azobenzene-Ç::arÞo>:yLic

acicL r,ras too insoluble in carbon tetrachl-orid.e to be stud.ied satisfac-

torily in this wqyo

IV.2 ft'rz-rliation of azo -carb acíc1s i¡r benzene

s ol.ut i.ons.

the cisç. tre¡s equJJibratior¡ of azobenzene anc Ir.any of üs

irerivatives ori irrad,iation in neu-i:¡'af solvents or aceiic aciA has .t:oc"

koor¡:n for some tir,eA4 and. this photochemical prc,perJcy of azobenzen:;s has

B5

20

rR

A

N

S

tIIil

rrT

À'[Ttl

c

E

11

40

60

o^

7500 7300 j 100 l, cü*

fnfrared spectrum of azobenzene-}-carborrylic acÍd in

carbon tetrachlorid.e at concentratioas 5.tx1O-7rJ- (1cm. ce11s)

(- ) and 5.5x10-4lu ( 10 crn. ce11s) (-----)

^

1

\

IìIIII\tt¡

IIII

tI¡¡IIIIII

Figurc: 2

96"

been utilized. in the preoara'üiorr of pure cis and. t::a.ns fo"r"".8ó-88 Azo-

benzene ancl m:rny of its d,erivaiives (obia.ined. usually as the l;r-'a-ns form

by old.inary methods oÍ' preparation) after irracLiation in organic sol-

verìts (usualIy petroleum e'rher) are subjected. to chrronratograplly or"i al',-;niina

a¡d. the ci.s arrr.f tra-ns compoilrlcs se;oara-te as two band.s.87288 the c-j-:r

isomer j-s j-nvariably more st¡ongly absorbed a:lCr the tra:rs isorler is easily

eluted- v¡eII i-n aclvance as the first bando îhe ci-s isoners of ihe substi-

tuted. azobenzene-z-earboxyiic aciCs do not appear 'üo have been prepared.

so fat (:-t i-s assr¡ned. that the synthetic azobenzene-2-cat'aotrylic ac:-cis

are the trens isomers)o Attenrpts have therefore been rnade to 1.:relai'e

these c-is isomers.

Since irrad.iation, followeC. by chronatography, has been used

for the preparation of cis-azobenzenes generalryr86-88 the same method. r'¡as

ad.opted. for the preparation of gþ-azobenzenê-Z-citrboxylic acid.so Acccr-

dingly azobenzene-2-carbo¡ylic acid 'lvas irrad-iated irt bezene solution in

a mercwy lamp reactor arrd. the soltrtj-on rqas chromatograrpheC on a colu¡m

of silica (alurnina cou1d. not be used. as the ad.sorbent as azobenzene-Z-

carboxylic acid.s lvere strongly ad.soioed- on the column). Repeated. irra-

d.iation of the solution a¡rd- chrornatography d.iô not forrn the expected. tr,vo

band.s attributable to the cis and. tiie tre4q isomerso Instead. a light

yellow ba¡rl l'¿as founci to separate frorn the maj-n band. v¡hich increased- in

intenci-ty on prolongcd. irrad,iation (50 ftours) " Tho first band. lvaEi eluted.

ancl 'che prod.uct v¡as i-d.entifiecL as the d.ecarboxylated. prad.ucto Atterapts

to prepa:r: the glg .l+t-chl-oro- and. 4r:rnethyl-azobenzene-Z-carooxylic acids

E7.

by this method. also proved. of no successo

The faiLure oÍ' azobenzene-2-car.loo>ryiic acids to fotm tÌ:e cis

isoimers r.ras not very surprisi-ng, as.oaral-l-el- carses vrere reported- in the

literatureo l¡n/leen a strong-Ly conjçgating substituent such as an a;rino:aa

acetylarnino or d.imethylanino group¡ v/â's in the À-position, I{a:'tJ-e¡l'anCO? OOc) ¡r eu(J

Coói<'ó¡served. that the correspond-ing solutions darkened consid.erabiy on

j-¡.rad.iation j-nd.icating ¡!ry --7

cis isomerizationo these isorners

appeared to be so short-lived-, horTever, t]lat they could. noi be esi;j¡n¿ted

photometrically;86 .na d.urirrg atternpted. chronatographic separati'on od'y

ind.efinite rrtailingrt ancl appearance of subsid-ia4/' zorres l'¡ere obseivea.

This ind.icated that the ci-s isomezs had. been formed. but none could- be

actually isolated. 87 eBB

ri,fhen azobenzene \¡ras substituted. with a hyclroxy greup in 2-

position the compour.d. exleibiied. phototropism88 unh"t exposed to unin-

ter.rupted ultraviolet 1igþt (the solution d.arkenea) Uut reversal- of the

spectrum to that of the stable fo¡rn lvas so rapid'ohat it l'¡as i¡npossible -uo

obtain anything but a qualitative indication of change. lhe instabil-ity

of these cis o-hydroxyazobenzenes (1f5) ancl g-hyd.roxyphenylazonaphthalenes

(lfe) vrere attri¡ute¿89 to the interrra-L hydrogen bonding j:r these mole-

cules rhich makes the tre¡s form extraord-inarily stable.

(115) (te)

BB.

Studies of infrared absor.otion spectra of the neutral conpounds

have provid.ed. confir¡ration for the interrral hydrogen bonding in azo-

benzene-2-carboxyJ-ic acids and. this coufd possibly account for the ins'ta-

bility of cis-isomers in these cases. The hyd.rogen boncling in azoben zene-

2-carborylic acid. and the conjugative effect of the carboxyÌ group irr ihe

2-position lower the double bond character of the azo linkage e.nd. hence

a rapid reversal to the rnost stable form is conceivabfe.

II

+

++ <+(rr)

Stud.ios of the photocì:emical behaviour of azobenzene-2-carboxylic

acid has been extend.ed to {'-chloro-, 4'-methyl- and. 4'-dimethylarnino-

azobenzene-2-carboxylic acids. fn all these cases slow decarboxyla'cion

was found. to occur and. the corresporrdi.ng 4-chloro-, -methyl-, and 4-

dimethylaminoazobenzene rlere obtained. ft is significani that neither

azobenzene-4-carboxylic acid nor azobenzene-]-carboxylic acid undergoes

photochemicaf decarbonylation und.er theso conditions. This indicates

tb.at zwilterionic forrns of the azobenzeno-2-carboxylic acids couid play

an essentia] role in the photocl¡enical decarborylation.

Support for this suggestion v¡as obtained. r','hen irrad.iation of

anthranilic acid. and t{-benzalanthranilic aciC r"¡as carried out un<Ìer the

sare cond,itions (except that an atmosphere of nj-trogen v/as used. to prevent

B9o

oxiô.ation of the prodr,rcts) " It t'.ês forìnd that d-eca.r:bo>:yla"tion occ'ürreC.

in these câses also and. ani-l ine anci benzalasúIine respectiveiy vrere ob-c)^

tained.. the observation mad.e by Sujishirrc ,t" f'na.t photochen:rcrrl ó.ecar-

'ooxylation of anthrarrilic acid- occurs l¡hen iradiated- i-n aqueous solution,

but not in soCj-uri hyd,roxid.e (O.O'l [) o" hyctroch]oric acicì (O"Ot il) solu-

tiorrs, ad.d. f\irther suppoit for the assuirpiion that ihe z',vi'c'cerio¡l-ic forrs

play an essentia-L role j¡r the pho-r,oche¡Hlcal d.ecarbo>çyLation.o4

A reaction of reiated na',,ure Ì'r'as re1rcrtei. recent\yl' tthen

pho';ochen'ical- d.e-ace'boxylatj cr vÊs obserr¡ed. on ii-¡'ad.iation of acetyi-

salis¡rfiq acid. in acetic acid- soiutiorr v¿ith a ned"i-u¡n-pressure lne¡cury arco

Tlre pz'eserrce of the ortho ca.rbo:ry substiiuent appears to be rLee...:'si1y '1oÍ'

Ce-acetorylation, as g- and. ¡-acetory ber:zoic acid.s and ethyl-c-acetoxy

benzoate urrd.er the sa¡re cond.ii;ions yi-eld. rn- and ¡- hyd.rorçybenzoic acið.

and. ethyl salicylate respectively"

nI"j A cornpara,tive stud.y of the ra-te of cyclizal,Lon of azoben:lene-

2-carbo

It has been shor,#1 tnrt for a satisfactory aeternina-bj-on of

quantwn yield.s and- of the effect of srÈstituents on ihe rate of cyeliza-

tion the availability of pure cis and- ira¡_s isomers of the azobenzer::s

and. the cyclized. proCuct benzop3 cinnolines rvere essentiaL. Since the

pure cj-s isomers of azobenzerre-2-carbo>rylic acid. ancl j-ts stfcstj-tuted.

d-erivatives coul-cL not be obtai-ned., ';ire previously ernployed n:ethod. for

tiie d.eterr¡rination of quanturn yieit for cyclization coufd. not be used. for

these compound-s. Hov/ever a comparative stu{y of the effect of suostituents

90"

in /,.- a:od- À-r -posi'cioris orr the rate of cyclízat'torr of azo'benzene-2-

cazboxyiic acid. on irrad.iation in gZl,L sulphuric acid. r"¡as ur¡d.ez-Lal<eno

the irrad.j-a'oion of solutions ( 1.i x f o-5 l,N sol-u-,ions was carried- ou'c

und.er a.l¡rost Íd.enticaL cond.iiiors and. the change in opticai clensr r,y o!

the lorrgest lvavelength absorption band. in each case of' tkre reac'Gion scl-u-

tion rzas piotted. against tfurre (^]ìigr-'" J). It t'¿as found. '¿in¿'s azo''¿erlzei\e-

Z-carboxylj-c acicl clrcLizeö, faster th¿-n the o'r,hrer four suJ¡stitutec azo-

benzene-2-calboxy1J.c acidso The raies of cyclízation of thc ît'te azo-

benzer'e-2-carboxylic acid.s d.ecreased. i:: the follovring ozrl.er: urrsubstituted.

)L7cL ) 4o -"i ¡ 4-Me ) 4'-I{e. There v,^a"s no cäz'ect correlation betv¡een

the rate of cycLlzation and- 'che effect of sul¡stituentso The obses'¡aiion

that J+-chlorc- and- !.-metl¡ri-azobenzene-2-carbo:qy1ic acid.s cyciizec i'aster

tha¡l the correspond-ing jar-chloro- anci. l¡r-rnethyl d,eriva,tives cou-Id- be

satisfactorily explained. vrith tLre aid. of the pro,oosed. meclianism for photc-jt

clcLlzàT,rofio

Since the cyclizatlon of azobenzene ard. its d.erivatives is

knol'r'n to occur only 1n the presence of strong aciCs it see¡ns that one or'

mcrre steps of the reaction are d.epend-ent on 'alne azo conporinij. being protorr-

ateC.o In the case of azobenzeÐe, since the molecuJ-e is syÌrunetrica.I, the

cyclizj-ng species of 'che cis-conjugate acid. can be of onLy one type

irrespective of lvhich nitrogen is protonated, but lyhen an unsJn,ne-brical-ly

suLrsLiLuLeü. àzçIteitzvt¡c is ¡,r'uLur¿¿¿LscL Llit¡ eis-curijuga.tu acirÌ car: be of trvo

types. The rate of cyclízation of'both the speci-es could be expected. tc

be differeni,

o1

^É

0.4

0.1

0"2

0r1

\

\g

\

\\

\

\

c0

P

ma

ïc

L

D

E

N

e

IrY

\\\\\\

\\\\

\" ----.._...-_-

1?7456789101112

frraCiation time in l:ours.

Change in optical d.ensíty of the longest y¡ûveferlgth absor'ption

ba¡rd. of ezobeo%ene-2-carborylic acids¡ unsubstituted (-"---), {-chloro

(*1, 4,-chloro (-..-."-), 4-nethyl- (------), {'-nethyl (-*-"-*1.

Figure 3.

-/ce

++H

R

+H+

ßr)

or

or

Ißz)

+H

(66) 1ot)

As suggested. earlier, in the case of azabenzene-2-carbo>ry1i-c

acios it is conceivable that tì're cyclizing species are the cj-s-conjugate

acid.s ',','here 'uhe O¡nitrogen atcm of 'dne azo linkage is protona'cecì." οe

probability of some protonatj.on of the p-rritrogen atom in strongly acicì.ic

solution, ho'À'ever, couJ.d. not be d.iscounl"ed.o trn substi'i;uted azobenzenr)-

2-carboxylic acíd.s the rate of cyc1.ization wiJ"l be d.epend.ent on the

posi-tion and. the electn¡nic effect of the substituent.

ïn the cis-conjugate acid. of [r -chloro¿'zober¿ene-2-carboxyJ-ic

acia (t17) the electronic effect of ti're chlorp group, v,'o'¡J.d. be expecteC

to hind.er the cyclizationo the +1,( effect of the chloro group rvouid

red.uce the positive charge at the prutor.,.atecl nit:rcgen anC. hence the 6t-

and 2r -positions lzhere the d.evelopnent of a positive charge is esscntial

for the cycLizati.cn accord"ing to the postulated. mechanism" Holvever the

93"

L,I

4et. ¡+

2tc1

¿+6

+

(117)

2t6 6

(tte)

+B

JIl

-I effect of the same group vrilt ind.uce a paztial positive charge at

the 6r- and. !t-positions.

In the c is-conj uga'ce acid- of ],.--chlo ro azober+zene-2-c ar-co:'ry üc

acia (118) the -I effect of the chloro group is expected. to increase -,he

trnsitive charge on the nitnogen and hence at the 6t- and. 2Î-positiorts;

and. cycli-zation wiII be facjlitated.o But the -I ellfect of the chioro

grþup wj-II red.uce the developnent of a negative charge in 6-position.

Since thre probability of d.evel-opment of a positive charge in the 2t - or

the 6'-position in (tt8) i-s much mo¡e than j-n (117) ihe cyclizat'ion of

þc}:1oro azob enz ene- 2-c axboryl ic aci d- p roc e eds f as te roI

In the cis-conjugate acid. of 4r -üiethylazobei:zerie-2-carbo:g¡1ic

ac:-a (119) the +I eîîec'c of the rnethyl group r.¡oulcl tenC. to red.uce ';he

fornation of a positive cha::'¿5e at the 6t- o:' fine Zt-positíorr and- the

tLto

cyclization vrill be hin eredo 1,,tiere'as in ihe cis-conjugerte acitl lf

/a-nethyla zobenzene-2-certoory:.i. u."ia" (lzo) tn" lf effectv¡cui-d. increa.se

Me

+ p +

(tzo)

HO

(11e)

the negative charge in the 6-positiort anù. the fo¡nra'cion of a posJ-t,i-ve

charge in the 6t - or tine 2t *position vv'ill not be affected. to 'ühe saí:e

extent as i¡r (119)" Ahe cyclization of 'chis ci-s-conjugate ac:-a (':ZO)

shrot¡l-d. therefore be faster tha¡r the cis-conjugate acid. of 4r -rnethyi-

azobenzene-2-carbo>q¡lic acid. ( t t 9) "

This exptanation appears to apcount for the observation

tlrat l¡- chloro- and L-me ti;nyJ-.azober,zene -2 -carbo>yIic acid.s cycl ized.

f¿r-ster tharr the correspond.ing l¡-r-chl,oro- and 4'-metÌ5rl substi'r"uted. ezc-

benzene-2-carboxylic acid.s, However the .obse::vation that azobenzene-Z-

carbo4ylic acid. cycLized ¡rruch faster i;ha¡r the sr-:lcstituted. ones coufcr-

not i;c explained- satisfactor"ily. It is concej-vable that substituen-r;;

in azobenzene-2-carborylic acid. probably lovrer the Sfl:=".f: ratio d.'.:-ri:ig

trans =i

cis photoequiJ-ibration. the increasi:rg eLectron release or

95.

v¡i-blri.rav,¡aL from the 4- ard 1at-position couid jrtcrease the b¿r.sici-i;y of

orie or the other ni-r,rogen of the azo group9z-gL' and. lovær the cloubl-e

bond- character of the azo Linkøge, and her:ce +,ffeci the stai:,iIity of the

cis-conjugate acid.s. lLre variation j-n the rate of reactiorr for photo-

chemical cycLization v¡i-th substituents m4y also reffect a charrge in the

ra"ie of ¡gn-productive processeso

96"

Expe ¡-i.:r.en-ba-l"-+

Pre¡ara-tj.on of tht': e.zo co,:pour¡dso

AzaTtenzer;e-z-c l-c

this compouncL v¡as prcpared" from methylarrtJ:rari-iJ-dce arrl ni'crosü-

benzene by a previor:sþ d.escribeC- reihodo After recrystal,Lizatiori the

pnrouct ha.d. m"p. g¡"jo (tit" u95 95o) "

L-.Ch l-o rp azobe rtz,eî,e*?--aa r^'hnr¡vJ i c -¡i,l

A njxture of ¡-cLrlorsrritrosober¡,zer,e96 (g,¡ g) ar.c. rnethylanthrairj--

late ( l'l "5 e) in glacial acc:ric acid soLution (lO m1) vras heated on a

water-batfr at BOo for 48 hourso Ehe cmd.e pnod.uct of the reaction rva.s

pr"ecipitated. on d.ilution of the solutiorr with water" fhis tvas e>:tracteð

vrith light petrolo The extract was washed. successir¡eþ vrith dilute hyd-ro-

chloric acid., aqueous sodiun bicarbonate, anC r,¡ater and. then d.riecì (--¡V-

C.rpus marSOU) o Chrrcnatography of the extract orr a colur,n of alurnj.na, antCr.

elution of the first (red) banC.rvith benzerrc/Light petroleun (t:4) IeC. to

the isolatíon of pure methyl l¡t-ç¡l"toazobenzene-2-carbo4ylate (9.5 g).

lhe ester sras hyd.rrclysed. in boiling ethanolic sod:ium hydro::ii.e solution

$%, SO ,rf) for /a. hours, the resulting solution bej¡g then diluteC. -,'.-j-';h'

water, boiled. j¡r old.er to re^r:-rve niost of the ethar¡oI, the product vlas

obtai-rred. as orange-yellovr needresp flop. 1670 (-l.rr.u97 ,66o)"

ô7)lc

l'-r *I,lethvlazoljcnze l'Ie)- 7-.Jn trrsù',".y1-i c a c'j il"

/r nr-lxture of nethy]-anthr¿nilate ( "ai "5 g) a:erl' ¡-rrì.'bro¡iÚ-

-bol-uene (g g) in glaci-al acetjr-c acrd- ()O n",l-) 1'res \¡rarìrìe'i oi: a q-,a-5';7-þ:i;i

at EOo for ,!O hours. lletiryi -i¡rmethylazobenzene-2-carbo>l¡rJ-ate '¡&s isc-

lateC. froin the reactiou rú,:l,uIË as in tne ab'¿ve experinenb and' hyôroiysed'

by reflu;iirrg ili: l'ribh etiralol-ic so,i.ium hyùru;<ide solution. lhe czu'le

ploduct (6 ù o'piai::ied on acidification of the allcali:re hycl:'clysis nÍx-

tun= , 'rvas crystlrLiised. f rom e'¿h¿:lolo /a¡ -ìiiethyJ- azolÐenze:Ic-2-carbo:iyLic

,¡ras thus obtaj¡leo as ol:alge-yellow crysbals mopo "ú5o (LL-v.93 ''¡ro) "

L¿-Chl-o:cc az cir: enze: nei- 2-r:¿:.cboxylic ac :id n

-liethyl- 5-chlola- 2-arninobei'\t oete \'Êì s prepa'rot1 f l.o¡n rne'i;|1yi

anthrarúlate ( ZO g) by the acticn oÍ' suj:phuryichloriôe (20 g) in ether

(¡CO of) using a modified. me',iroo of El-Ier t.C K1e**"99 Chrurnato¿:'aphic

separatiot: of the products obtai:reC. on basificatioir follcwe'1 by c'r"ys-

tai-tization f rom light pe'urui afford.ed. me'thyJ- -!-cirlorrc-!-arúnobe':zoate

(rz e) as colourress plates¡ rnrpo 690 (rto: 69o)"

IúetÌ1y1 5-chforo-2-¿:.mincþerr"ott"i00 (¡ g) r'ras con<i.enser1 with

nitrosoberrzene (+ g) in giaciai acetic acid. (10 mf), the teinperaL':i-e of

the reaciiolr mjxture being nrai-n'cained. at 8Oo for 48 hours" the cì:;'c'¡a-

tographic isolation of methyl--4-cìf"oro azobenzene-2-cafboxylate a-nd sub-

sequent h.yCrulysis to 'uhe fTee aci-O r'¡ei'e effected. as ii: 'uhe previous

cases" The l¡-cirloroazobenzenè-2-<aribo:cyiir: acid" (t"5 g) so ob'oained

forirred. orar-ige needies, m"po lzTu çii't.trD1 126-127o), rvhen rcczyst;r]-Iized-

frorn etiranolo

98"

ezobenT,e rb Iic

A sol-ution of !-ne'cjoyl-2-a-ninobenzoic aci-l (prr:i:ared. ac.:orJi:'rg

to the method. of Find.ekl ""1A'

fro¡n n-r;cluic aci-d by nitraiion anù separa.-

tion fotlolæd. by tÌre red.uctic¡n of 2-ní-u'-o,-J-:nethyl-benzoic acid-) (lO g)

in methanolic hyclrogen chlo::id.e (50 m1) vras boiied- r¡:rder rr:fh¡x foi: ô

hout:s. The solution v¡as then concer:Érated. to a s¡nall volure eq.'¡¡g,

arrd. ùilute¿ I'rith aqueous soclii¡n bicarbonateo The pi:ecipít¿-'çed' este¡: i..'as

extractecL vrith benzene artd. the extract after being d.ried. (lVarSOU) p !.'ras

evaporated. to drynesso The residual- methyl 5-nethyt-2-anÉnobenzo*úe 1#zs

recrystallized. fron JÚ/o aqueous rnethanol, mop" JJo u

lhe methyl ester (¡ g) and nitrosobenzene (+ g) ve;re us¿å ir:

the same nanner as described above to prepare methyl -l¡-lr,eth¡tazoпni'c:-'

2-carbo:cylate, rdrich r'¡as j-n turn hyd.rolysed. to the caduo:<yiic aciC'" 0'n

recrystallization frcnn light petroleum 4-nethyl-azoben::ene-2,"çaqbo-lryliq

aci4 was obtained. as orange need.lesr D,Fo 99o (pound.: C, 7O'2; H, 4"8;

N, 11.7. ar*nt ZNZOZ

requires C, JO'O; H, f .O; N, 11 .T/r).

Phoicchemic al, c¡¡clo dehvd--rr: ge natio'ns "

L zobe\zene-Z-c ?\b o>::/Lia acjð..

A soLrrtio,. of azobenzene-Z-carboxylic acid- (Z.O g) ín 9&i¿

Analar sulphurj-c acid. (120 ¡¡r].) ruas irracliated. in the mercury-la.ni; rea^ctoro

the reaction appeared. to be ccmplete after'tr1+0 hours, there being iro

further change ín the ul,travi-o1et spectrum. Ihe react;lcn mixture v.¿ls

then poured- into ùcè-.,,eter ('! t) and. the precipitated' solid (S) vøs

99"

coLiected.o ÎÌre acid.ic solutj-on y/as partially ner:t:calized anJ. extz'acied.

rellea';ed.1y vrith ethyL ace'ca'ae unì;ü the organic la,yer l,'ras col-ourlesso On

evaporation of the solveni a pa-1e yeliorv solid. (S.1) v,as obt¿-rined* the

acid.ic solution vøs then basified. (sod.ium hyd.roxid.e), extrac j;ed several

tjmes .,rith benzene a¡d. the solvent evapo:raterl rrìren a le¡non yellorr solià

(SZ) vias obta-ined.. The solid.s (St and 52) v¡e¡.e confoined. a-:d'¿r'eaied',',-i-;h

sLjJ-ute ammonium hycroxid.e solution a.nd the insoluble material e)rLvîacJied

vrith benzene. Evaporation of the benzene layer and recrys-r,allizati¡n of

tlie resid.ue (0.05 gt z.J'ft yl.e1d) fro¡n ethanol yield,ed. ycJ,loi''r neecl-,;s oÍ

benzo[c'l cinno]ine, lvhich r'¡as id.eniifieC. by d.j.:'eci comparison (rnixed. mopo

a:rd. ir¡.frared. spectrum) l,rith an authenti" ""*p1""10JThe ar¡noniaca-l solution on aciclification l*it'h d.ilute hrrd.."c-

cirioric acid. afforded. a pale yellorv solid (l '5 g, JJ/" yiel.:a) , Cn r"e-

crystal.lizztzon from toluene benzcp]cirxrofine-J+-car'ooxylic a.:id. r'¡as

obtained. as pal-e yellorv needles¡ fr"p. 283-285o (þ vo-.,ro) u-Lote o:r ¿.i¡i,j:ced.

with a pzevi-ously prepared. sampleo 2g

1,,-r -0 hf o ¡' oaz ob en ze ne -2- c a::b oxylic ac id.

4r-chloroazöbenzene-2-canbo4ylic acid. (Z g) tn 9Üi6 Anal-ar

suiphuric acid. (120 mI) vras irrad.iated. in a Pyrex reactor fo:r 1BO hours,

lihen the reaction appeared. to be cornpieteo 'Ihe reaction mixtrrr\J orÌ being

wo:iiecl-up as i¡¡, tl're fole¿oiiig experir,rit-:nt yieJ-ùecl oirly 'l-o::obenzo ic] *

ci:nnol.ine-@ (1"5 eo 7f:/") ,¡¡híc]n on recrystalLtzatíon from

toiuene formed. yellovr p3-a'ües mop. Z7Z" @ vi:-cr.ro) (I'or.rnd: C, 60"O; A¡ 2,7i

ll, 10.7; cL, 13.1o Crffl*zO, reguires C, 60"3; H, 2.7i N, 10,8; CJ-rljofio';o

'! 03.

/"ù -1,{e tlryl- a z ob enz e ne - ?. -c at-ø oxl¡1. i c ac idn

À solution of l¡r-inethylazobenzene-2-carito:cylic acj-d. tn 9Ui"

Analar suiphu:clc acicL (i2O rnJ.) r'&s irracliated.v,'ith a mercury-qua:iz Lamp

u:iiI its ultraviolet absorptj-on spectrurn showed thai the reacticri lvas

vi::tually complete (Zlp trou="s). On 'rorking-up the reaction r.ixtu:e as

in the above expe:'iment 9-tne,!!y}'t9"zq fql cinnoline-+-SgÈ4ig a.çl'f l'¡as

obtained.o this on recrystall-ization from tolue;ne foirieå yellorr neecLles

m.p. 2680 (þ vacuo) (I'ouna: c, 70"7i H, )+"4i N, 11"5o "t.,*n1 CrOz

requ-ires C,70.6; H, 4.2; N, 11.11¿)o A small amourt of an aLkali

insolu'i¡le (d.ecarbo:cylated.) prorluct r,ßs also isoLa'r,edo this could i:ob be

crystaltized. bui j-ts ultraviolet spectrum in ethanol was sj:nilarEc 'r;hat

of 2-methylbenzo f sl cirrnoline.

L-Chlo rc az obenzene- 2-o arb ox.yli s acid-

A solution of 4-chloroazo'oenze^e-2-carbo:qyli-c acia (0.¡ g)

ín gfii Anal-ar s.ûphuric acid. (120 ml) vas irrariiated. r^¡-ith a merclì.ry-

quartz lamp for 18 ho'urrs, v,hen the reaction appeared. virtualiy cornpleteo

Fro¡n the reaction rnixture, the only prod-uct 2-chlorc'r:enzofclcint:ol-ine-

carborylic acid. (O.tA g, 6oli') v¿as isolated. as in the -r:r'evious ex*ceri-

ments. this on recrystaJ-l-i-zabíon from toluene fozrred- yellow plates m.po

2t¿ro G.lq vacuo), (Found.: cr 60"4; H, 2"!; N, '11"0; Qr, 13"i" cr-¡l-fNzoz

reqúl-res c, 6o.3i H, z.-l; N, 1o"B; cr, 13.7f/").

tr-j,,le th.yl a z ob e nze ne - 2-c ar'p oxylic a.c;i4.

A solution of ,¿+-methylazobenzene-2-carlio4y1ic acid. (0"¡ g) in

:- i

101 .

!87á sulphurÍo acid. (tZO mf) v,as irrad.iateci untjl- the:reaction appeari;å

coi.rplete (ZO houz's). The ¡eactj-on nixturc on being worlced-up as :n-ti-re

earl-ier e:qgeriments yiel-C.ed. orúy Z"^"rn.Mg ]-Tt a.rb<>:-:r --:.+

acig (O"19 g, 61oÁ yield.). On recrystal.l-ization from toiuene yeJ-low

needles were formed mopo ZiZo @-@g) (lìouna: C, /O"B; iIr 4"5; Nr 11"4o

a,,.nrONZOe requires C, 70"6; H, 4.2; N, 11.91ù.

Phot ochemica] d.ecari: lati

nach of the following azobe'nzene-2-aarltoxylíc acid-s in a soLu-

tion of benzene was irrad.iated. in a l...ate¡-cooled Pyrex pho",,ochem:-c;t te¿e-

toz'vrith a high-pressurE mercurf-euartz lampo After the irrad.iatiorL2

the solution vras concentrated. to ¿ s¡¡¡l'l voLume (tO mf) arrd srioj;e;-;'Lc

chromatographi-c separationo Àlunina lvas used- as the adsorl¡ent ir^ ';k¡e

case of 4r -d.imethylariino d-erivatÍve and silica gel in the reniaining cases.

Eaclr of the d.ecarboxylated. prod.uct v¡as eluted. vrell in ad.vance of 'che u¡r-

changed. naterial. The pnrd.ucts were id.entified. by d.irect conparisoi.

(mixed. m.po and. infrared. spectra) with auttrentic samples available from

earlier worko

A z ob enzene-Z -carb oxylic acid. "

A.zoheiwene-2-carJrorrylic acid (2OO ng) in benzene (too nf) on

i:rrad.iation for 50 hours v¡ith a meruury-quartz lanp anC chromatog::aphy

of the products on a coLumn of silica yie1d.ed.'azobenzene (10 ng, yíeLð.6d1)

o,"'p. 670 alone or ao.mixed. with arr authentic sarnpleo The infrared -;--u1;z'r-;fn

v¡as identical. with the spectrum of authentic azobenzeneo

102.

In a separate experj¡rent azobenzene-2-can'boxJtLic acid. (!O lng)

lvas irrad.iated. in benzene (llO r*f) for 2JO hours. Cieromatographic separa-

tion as in gre above experjment yie1d.ed. azoberwene (t8 mgic'1.1¡f7á tie}a),

Lf 4h1o ro azohenz-ene - 2-c a:cb ox.¡l i c a-c i d""

Irra,Liation of 4r -chloro azohenzene-2-carboxylic aeid' ( "2 A)

followe,i by chromatographic separation as in the foregoing case yield'ed'

þclrloroazobenzene (tO rg 9.6% yiel,d), rìrpo a¡rd. mixed. m.p. r'ritLr arr

authentic sample, 87oo

| -ì,{e Lazo lic

Chromatographic separation of a¡r irradiated benzene soLutj-on

(f fO mf) of ¿+'-melhylazobenzene-2-carbc4ylic acid. yield'ed' þmethyJ-azo-

benzene (tO mg 9.6% yieffi) m.p. anfl nrixed. mopo with an authentic sarçie

4t -Dimethylar¡rinoazobenzene-2-caË'po:ry1ic acIl. '

A benzene solution (ttO mf) of l+t-d.i¡rethylanrinoazoltenzene'2-

car.ìro:qy]ic acÍd. (O.Z g) was irradiated. for !0 hours and' the products være

chr.omatographed. on a column of alumina using benzene as el-uanto lhe

yel1ow fraction rvleich eluted. v¡eIL in ad.vance on evaporation gave /¡--d'imethyl-

aminoazo'o enzerle (tZ ng) as a red.-brovl"n solid, mopo âlone or admixcù v¡if;h

an authenti.c sample, 116-1174.

o71 o

1ot"

Azobenzene-J-carbo;ÍElic acid. ,

A benzene solution of azobenzene-J-carborylic acid' (.2 g) I'ras

irrad"iateð with a merpury-quartz lamp for 200 hours" Evaporation of the

solvent a¡d" chrrcmatography on a column of silica sholved' only one single

band. attributable to the starting rnaterial'

ivzolte carboxvlic aci-C'

A benzene solution (tf O mf) of azobenzene-þcarbo4¡Iic acid'

(O"t g) was irradiated. witkr a mercuIy lamp for 200 hours, the solve;-i¡

evaporated., and. the residue chromatographed. OnIy one single ba;rd' beiong-

ing to the starti-ng rnaterial was formed.'

Benz ra¡rilic aciô.

A solution of benzal-anthranilic acid. (0.5 g) in d'eoxygenated.

benzene (f lO rnf) was irrad.iated with a mercur1¡-quarbz 1a.mp in a Pynex

reactor j¡e a¡ atrosphere of nj-trogen for 2oo hou::so the resulting solu-

tion was sha-lcn with sod.ium bicaCoonate solution to remove the unchange']'

benzala¡thra¡rilic aoid. and. the benzene 1a¡rer d.ried. a¡ld evaporated" lne

oily resi-due (¿'O mg) on crystallization from metkranol gave benzal-a¡j-line

(tO mg) mop. 1,1o alone or adriixed 'v'ith

an authentic sarnpleo

Àn'Lhranilic acid"

A solution of a¡rthraniiic acia (0.5 g) in d.eoxygenated benøene

solution (f f O mf) ,r¡as irradiated. rvith a higþ-pressule mercury-quar1;z Larrçt

for 200 b,our.s under nitrogen atmosphereo The unchanged anthrar¡:ilic acid'

'10h.

.¡,.,Ë.s rpmoved. by shaking lvith d.il-uie sod.ium hyd.rorid.e and, the ber'zer*: solu-

tj.on ,åried., and. nrj¡<ed. with pher¡ylisothiocyanate (O.t rnf) and Ylarrredo The

solvent was then evaporated and the resid.ue vn.shed. with light petrol- a:rd.

crlystallized. from agueous ethanol; NrNr -d.ipkrer¡rlthiocarbar¡rid.e (ZZ n'€)

(fonned- by the condensatíon of aniline and. phe4ylisothiocyanaie) '¡¡as ob-

tr.ined. as shining plates m.p. 1!Jao alone or ad.rni:<ed. with an autJ:entio

sampleo

In{Êa.red. spectrao A Unicam SPTOO spectrophotometer was used on d-oubie-

beam operation in th,e grating region for the d.etenuination of the irfi'az'ed

spectra of azobenzene-2-càrboxylic aciås a¡d azobenzene-J-carboxylic acid-.

Spectroscopic grad.e car'oon tetrachlorid.e was employed. and reasurernents

v¡ere made i¡¡ rratched pairs of silica cells (1 cm and. 10 cm) rvhich ha.d-

trar:sir¡-Lssion vaLues greater øralt 857á througþout the ra-nge $6OUZIOO "*-1)siud.ied..

Rate d.ete rrninations.

Stock solutions of (1.5 x tO-5 g) azobertzene-2-càTbox.ylic acid.

a:rd its l¡t -chl-oïrc-r þchloro-, 4.r -met$l- and. l-metk5¡]-d-e::ivatives Y¡err:

prepared. ín 9V/" sulphuric acid.o Each of these solutions had. an optical

d,ensity in the range of O.55 to 0"65 at the longest wavelength absorption

¡ana (4JO-la6O m¡r), Approximately J ml of the solution 'vas used' in eaci:

case for irradiation.

The test solutions anC. the tr,¿o solveni celJ-s containing 9g/5

sulphuric acid. were kept at almost equal distance on a cirpular platform

105.

v¿j-th the sourpe of rad,iation (ltr:-típs 16OYrr. I\tercury-lungsten lamp) in the

centleo The platforrrr'!'t'¿s mechanically rotated. at slov¡ speed to avoid

wrequal irrad.iation" The d.ecrease in optical d.ensity of the tes'c solu-

tiorrs at the longest wavelength absorption band. rras measured. at n:gular

intervafs with the aid. of an Optica CFU recorxling specttophotome'cer,

untjl the optica-} derrsity had. flroppefl to nearly Oolo the optj-cal d'ensi-

ties v¡ere ptotted. against time, and. the time reqrrired. for half change Y''as

noted.. The TabLe beLow sho.¡rs the change in optical d.ensities of aLL azo*

benzenes with irrad-iation.

0r:ticaI nsities of Az 2-carboxvlic ids at d.ifferent iniervals

on irrad-iation

Þchloro- l+r -cÌrloro Þmethyl Lr -urethylUnsubsti-tuted.

\optica-Id.ensity

0hrt]nr2}:rr

3}:^r

4hr5];,r7h.rthr1?)tr

lime forhal"fchange

)+38 t+ßo )+58 455

o"62

0"60

0"59

0"46

o"375

o"2g

o.20

o"15

0.10

455

0,58

O"5ì+

0"50

0.1+6

o"1g

o.33

o"26

0.19

O,13

UoO

o.3+

0.16

o"'13

0.06

o"55

0.l+9

o.43

o,335

o"25

o.1g

0.11

0.06

o.57o"53

0.48

0"¿ú

Q.33

o"23

Q.16

0" 11

0.08

1.2 hr 5.5 hr 4.4 hr )+,5 hr 6"0 hr

ciihtrI3R v

Photocheraistry of 2rzt -

azoclipher{ylmethane

106.

Phot ochemis tr]¡ of 2 . 2r -azocliphenl¡lmethane.

lhe pleot o chemical cyclodehrydrogenation of Z-metYryTa"zobenz e ne

has been sho'rn to proceed. partly by cyclization into the vacant 6-

posi-tion, and. partþ by cycLízation into the 2-position with ejection

of the metkgrl substituerrto2S In the case of the photochenr:ical reaction

of Zr\rí-trimethylazobenzene (18) in v¿hich.one ring has no ursubstituted.

ortho position (2- and. (-position) for cycliza;tíon, it v¡as for:¡d.29 that

cyclízatíon occurred. with ejection of a methyl gncup frorn the posi-tion

of cycLíza.tion. In ad.d-ition a small amount of 1'r}j+trirnethylbenzolS]-

cirnroline (æ) """

also isolated.o The,latteþ ''¡ras conceivabþ formed. by

rn-igration of a metÌ¡rl group from one of the ortho ¡nsitionso the possi-

MeMe

Me

MeMe

(¡a) ßg) (+o¡

bitity that migration of the metkgrl gruup occurred before cyclízatíon ì'¡as

consid.ered. unlikeþ und.er the conrì.'itions rtserl, althougþ such phot+-

cataLyzeö. intramolecular migration of alþ1 grþups are koownlol'-106 ao

occur vrrth ¡rad-íations of much shorter wavelengths than used. for the

cycL|zation of azobenzenesc A possible mechanism for the migration of

1o7"

the methyl group has been outlined. by Bad.ger, Drewer *nd. LewisSl (Scherne

3). The 1Oa, 1Ob-d.ifyd.ro-2r4r1Ob-trjmethyl benzo[c]cirucotine conjugate

acid. (121) wtr:ich is erçected. to be formed on ring closure, is first

envj-saged. as und.ergoi-ng a pr.ototropic rearrangement to give 6r10b-

c.i-Ìrydro-2¡4-1Ob-trimetlryl compounl (tZZ +tZÐ followed by migration of

the methyl group from the 10b to the 1-position to form t'kre carbonium

ion (1Zh). This j-on on prototropic rearrangement a¡rd. d.elgrd.rogenation

vrouJ.d. f\rrnish the fuIly aromatic compound. UZÐ.

In the photo reaction oî Zr)ará-trimetl¡rlazobenzene the for¡rra-

tion of.â sevêD-membered cyclic compourd., 2¡2t-azo-lþ-dLnetL¡yldiphenyl-

metkrane (12ò, S.rrvolving a methyl group and. further reaction of this com-

por:nd to the obse¡ved. proaucts (J!) by elJ-rnination of a metÌ¡rlene group

Me

Me

(127) (rza)

and (4O) by a rearrangement, lvas also conceivable. It uas, therefore,

thought d.esirable to exanine the photo-chenical behavi.our of 2r2t-

azod.j.pher¡ylmethane (tZe), Furtherrnore it uas of i¡rterest to see whetirer'

an ejeotion of the metlryIene group or el-imination of azonttrogen would'

1O8.

Mo1 Me

Mc

Me

-J+Il'3

MeMe

+

(tzt)

Iû ¿+H'

(124)

l*H

1

(tzz)

MoMe +

Me

EI

HH MeMe

Me

(125)+

+

ETfI

IfHMe Me

Uze)(tu)

Scheme 5 a

1O9.

ta-¡rc place on irracliation of ztzt-azodipher\ylnethane (te8) to give otÌrer

stable aromatic compoundso

2r2t -Lzod-tpheq¡lmethane (1ZB) was prepared accord.irrg to tlie

method. of TheiJ,ac1cer and Korndorfe rla7 ay the reductive cyclj-zation of

Zr2t-diritroùipherylmethane with lithium alunin:ium hyclrid.e i:r ethez'eal-

solution. Elemental anaþsis was the onþ evid-ence reported for its

id.entity. The mass spectrtun of tlie comporuicl was therefore nlrr arrå tl¿l;s

of the molecu-Lar ion fo'nd (rty'" 194) was in agreement with the molecular

rveigþt (tç+) of 2r}t-azodíDhenylmethatre. The ultraviolet spectn'm in

ethanol resembled. that of cis-azoberlzerre in ethanol'

2r1t -Lzodipher¡¡lmethane j¡ etlranolic or in benzene soiution,

ùid. not und,ergo ar¡r noticeable cha¡ge even upon prrclongecl irrad'iation

ar:d. the compou¡d. was recovered. quantitatively on Iencn/al of ihe solvent"

Horvever vtnen 1/l ethanolio sulphuric acid. (v:v) wrs used- as solvent, 2r2'-

azod.ipherSflmettrar¡e und.ervent a rapid photochemical reaction as shov':: by

the changes in j-ts ultraviolet spectrum and. by the d'eepening in colour of

the reaction n¡-ixtureo Ïlhen there appeared' to be no further change j'n the

uLtraviolet spectrum, the reaction mixture was worked'-up and' the proô'ucts

were separated by chromatography on a column of a]-umirra.

Initial fractio¡s from the ckrr"omatograrn yield.ed. srnaLl quantitics

of rinchanged. nraterial a¡c1 some unicl.entified' materiaf-. These l'¿ere foilowed

by d.ibenzo[gÉ] ll12] ai*""pin-11-one (129) @." 1O,,4 yield) , 2,2'-i'.1-a¡iú¡ru-

benzophenone (t5O) @. lO/" yield.) , Zr}t-d.iarninodiphergrlmetJrane ('¿l)

(*." 1516 yieLd) an¿ a comporincl (m.p. 262\ @," tCÍ; yie16.) r¡hich ha¿

molec¡-lar weigþt 210 accord.ing to its nrass spectrum, ind'icating that it

110.

could. possibly be 2 r}t-k¡rdraaodj-phenylmetha¡re (EZ) .

H

(12e) ( 1lo)

Ez

(ttt) (tz)

lhe str:Lrcture'of these prod.ucts werre elucidated' as follows:

the j¡frarea spectrum (C,UCfr) of d.ibenz.Fr$ frrZf at"o^pi¡r-11-one (129)

showed absorption at 1667 crfl (C=O). Its r¡ltraviolet spectrum j¡r etha¡¡ol

showed absorption ba¡d.s at, þO, 325, arÈ. à40 q¡ (tfre starbing material

showed absorptions at 21+5t 52Q, and. \JO mP). It therefore appeared' that

tLre ben4ylic metl¡ylene group lrL 2r|t -azod.iphenylmethane has r:ndergone

oxidation d.uring irrad-iation to give d.ibenzo[c;fl l rZ)ai^uupi-n-11-one

(129). The nass spectn:m of this conpor¡nd. showed a molecular íon ({e 208)

which was in agreement with the molecular weigþt (ZOg). Its meltin¿ point

on adnd:cture with an authentic sample of d.:ibenzo[SrÉJ þ rZ)a-i^uapir:,-11-

one (td¡aþ supplie¿ by Dr. R.B. Johnsr1he University of Melbourne) was not

I I t.

ciepressed, and tlie j-r¡frared. spectrum of the compound vras in complete

accordance with that of autl:.entic sample.

2rzt-Dianinobenzophenone (t¡O) was id.entified. by a cor.parison

(lnfrared. spectrum and. m:ixed. mopo) v¡ith an authentic sanrple prepared. by

i;he reduction of 2r2t -dínLtroìrenzophenone vrith tin and. h¡roroclúoric' acid..

the compound. from the third. fraction wìrich was concludeC" to

be 2r2t -ôia¡¡l-inodipherrylnrethane showed inflrared. absorption at J5OC end- at.l

13BO cn- ' (characteristic of Itü12), and- the compowrcl also forrned. an acetyl

d,erivativeo lhe melting polnts of the compouncl (tSl) and acet¡rl d.eriva-

tive were in agreement with those reporbed. i¡' the fiteratureo

The last compowtd which was eluted. from the drn¡matogram

shovred. ir¡frared. absorpti.on at 533A a¡rd. at 1615 cm-1 (secorrd.arSr -I,üi-) and-

at 1650 cm-1 (c=o). The molecular forrnula (a.f ,CrO) was d.educecf for

this compor¡T d. from elementa.l- analysis and. the mofecular weight (reolecular

ior, m,/e 210)" lhe structure 2r2t-hydrazobenzophernne (l5Z) appearcd the

most likely one for this compound.o Attempts to oxid.ise the comporinel to

d.ibenzoþÉ] f ,flaiazapin-11-one (129) were not successfuL. Àttern^ots to

prepaï€ thi-s compound. idependentþ by the alkaline reduction of (129) were

also u¡rsuccessful. The compouncl rvas not obta:i¡lecl lvhen the experir¡:ent lTas

repeated. a¡rd. further work tov¿ard.s its characterizatíon coufd not be

carried. outo

Ihe fact that there tras no reacbio¡i ulæ¡¡ a sulutioti of 2r2t-

azocliphenylmethane in 1"Ã ethanolj-c sulphuric acid. (v;v) was Left in the

C.ar.k a¡d that a rapid, reaction took place on irrad.iation shows that the

observed. products we¡e the result of a photoj¡iduced. reaction. Since

112,

neitlier a-n etlrlanolic nor abenzene solution appeared. to undergo change on

prrcIonged. irrad.j-ation, it seems that the conjugate acid' of 2r2t -azo-

ùipher¡rlmethane (llÐ is the reacting species. A,ltlrougþ there is in-

sufficient experimental d.ata to enable a reaction mechanism to be ad.-

vanced., some reasonable suggestions cart be mad.eo In vj-ew of the ellcep-

tionally higþ d.ehyd.rogenation polver of conjugate acicls of azobenzenes,

it m:ight be assurned that the conjugate aci<). (tiÐ of 2r2t -azodiphenyl-

nr:tha¡e can abstract hyd.ride ions from the reactive benzylic methylene

gr¡oup of (tZB) and. that the resuLting carbonium i-on could react fLrthêr

to give ðibenzo[cÉ] [ ,]aíazapin-11-oneo the 2rTt-hydrazoð.iphenylniethane

(llü, vdeich'¡rould. be formed. in the sj¡nultaneous reductlon process, is

lcrown to d.isproportionate i¡l acid. to give 2r2t -azodiphenylmethane and.

a_a72 rzt -ùísrnlnod:ipher¡rlmethaná" The conjugate apid of d.lbenzo Frg] [J 12] -

(ttt)

(ttz)

(tt+)

t t!)c

d.ia.zapin-11-one (tlù might al'so abstraci hydrid.e iorus from other sulc-

st¡.ates and. thus urrd.ergo ¡eduction to 2r2t -hycirazobenz;ophenone (152)'

Tlre Latter could. presumzibly d.isproportionate in acid. to give (129) and.

(rro).

No benzo[clcir¡noline type compou¡ds r¿erre detected- in this photo-

chem:icaL reaction of 2 rZt -azod.iphenylnrethane "

A slovr reactior¡ proceeced. v¡hen a soLution of dibenzo[Srf.l Ú râ-

d.iazapin-11-one (129)in1'Â',ethanolic sulphuric acJd. (v:v) rvas irradia-bedo

the onþ prod-uct isolated. from the reaction raixtrlre was 2r2t -ùia¡ni¡robenzQ-

plrenone (f¡O). It appeaïìs that the conjugate acid. of d.ibenzof-c r{] ta-

ùLazapi-n-11-one (llù rdgbt abstract hydrid.e ions from the solverit mole-

cules a¡id. that the resulting hyd.razocompound. coul-d. yield. 2r2r-d.iami-iro-

benzophenone (t¡O) on dispropori;ionationo

Tfl¡en a solution of Zr2t-azod.iphenylmethane in 9E% srrlphuri-c

acj-ci v¡as irraôiated- a slow reaction proceeded, md the only prod.uct iso-

l¿.ted- from the reaction mjxture wa,s a sulphonic acid, of conposition

"tftLNZOSS. Its ir¡frared. spectrum (trtu¡of) shov¡ecl a broad bancl j-n the

-ll35OO-Z7W cm region, with two ill-d.efined. peaks at 1i8O axuT JZOO c,ni1

(possibty fu¡), peaks at 167o crí1 (c=o) , t6zo crf,1 (}ü1) and absorption at4

805 and. 73O crr-l (characteristi.c of 'l ,2r4- and' 1r2-substitution) "

Dlazotízation and. coupling with atkaJ-ine p-nerphtirol formed a yerloiv {re

ulrich turns red. in acid.. the compourrd- could- possibþ be 2rZr-dianrino-

berrzophenone-5-sulphonic acia (136) " Further atten-rpts to characlerlze

rÌ.ris compor.rrd. couLd. not be carried. out because there was j.nsufficient

n'raterial,

0

i ¡4'o

(ß6)

SOJf)

MzHzN

115 -

Experj¡nenta]-

2 "

2 t -A z od.iphenylmethan e.

4r{.t -Diarninodiphenylmetha¡re lvas pr€pared accord.i-ng to the

method. of Sca¡ùarr1o9 ¡y the reaction of anil-ine ard. forrnald.ehyd'e i:r the

presence of hycl.rachloric acid. a.nd. purified. by recrystallization frorn

boilirrg water. A solution of 'lar/at-c'iaminod'ipheny}lethane i:r' sulphuric

acid. lras nitrated at temperatures belolv 1Oo witn funring nitric acicì., arrd.

the prud.uct so obtained. vras recrysta-tlized. from etha¡rolo 2r2t-Dinítro-

[rl+t -diaminod.ipherrylmethane vras obtaineô as orange-red crysiaÌs I iloP.

2O5o (lit "1to ,o5-206\" Deamination of the d.ia¡rinod.initro d.erivative,

by d.iazoti-zation wj-t:n J(" h¡pophosphorus acid. in the presence of cupric

oxi-d.er111 *^.r" 2r2r-d.initrod.ipher¡ylnrethaneo this was purified- by chroma-

tography on a colu¡nn of alumina foll,owed. by recrystallization from ligbt

petrol, mopo BJ"5o (tit.1Q7 83"5o).

Lithium aLuminir'¡m kryd'rid'e (r"o g) was ad'd'ed' to a sorution of

Zr}t-dínítrodiphergrlmethar¡e (t"O e) in ether (¡OO mf) in small quantities

with effícient stirring and- cooling, Trlhen the vigorous reaction subsiaed.

(after 20 minutes) tkre excess lithium atuminium hyd.rid.e was d.estroyea by

careful ad.d.ition of water, and. the ethereal solution v¡as ilecanted. and. the

residue extracted with sma-l-I quantities of etkrer until the ehtereai layer

was colourlesso The ether was then evaporated. off, and. the residue was

chrnmatographed. on a column of alur¡iirra uslng, light petrol as eluanto the

initial red fractions were d-iscarcÌed and the d.eep yellow fractions vàich

follovred were collectedo The solvent was removedr and. the residue (C"45 g,

-116-

6ú/i yíe1:ð.) recrystallized. from ligþt petroJ-o 2r2t,Azodiphenylme';ha:ie was

olrtained as brigþt yellow pratesr ilopo 11oo ( nt!7rcg-110o).

The ultraviolet spectrum of this compound in etha¡¡ol shovred.

absorption peaks at %2, J2O, anð. 455 lrrf" Its nìass spectrum shov¿ed. a

peak due to thre parent molecu-lar i-:on (n/e 19¿ù.

Irrad.iation of 2 .2t -azodiphenvlmetkrane o

In ethanolo

A solution of 2r2t-azodiphenylmettrane (O.Z g) in ethanoi (110

mI) was j.rrad-iated. in a $rrex reactor with a higþ pressure rÍErcur.,rr-aparLvz

lamp. there was not argr notÍceable change i¡r the ul-traviolet spectn^rr,

even after irrad.iation for þ0 hours, and on remova.L of tJ:e solvent only

starting material ïras recovered.o

SfuT:itarly, no reaction was obsenred' when 2r?t-azodípher¡¡l-

metLrane wa,s irradiated, i-n benzene solutiono

In etha¡olic sulphuric a.ci.d..

Pre1i¡ainary experiments, using sma-1l concentrations of 2r2t-

azodipher¡yl¡rethar¡e in 1% etha¡o1ic sulphuric acid. (v:v), shovred that a

rapJ-d. reaction occtl.r.ls vuhen tkre solution is irrad.iated, (faster in swrlight

than With a mercury-quartz lamp) o In a preparative scale e>çerjrnent

Zr2t-azod.Lphenylrnethane (1.0 g)r'd.issolved. il 1/á eüruriolic suJ'phuric acid.

(tOO urf), was irad.íated v'rith swrlight in a culture flasko T.he reaction

appeared to be complete after 15 hours, there being no firrther change in

the ultraviolet speotrr.mo The reaction rrixtr:re was basj-fied. with sod.ium

-117-

k¡rd.roxì-d.e, the ethanoL v¡as evaporated. a¡rd. the resid.ue was extracted. with

chLoroform. the red-brown residue obtained. on rerrlcval of the chloroforrn

was chromatogra¡ùred on a column of a-luminao Sj:c fractions were coll'ected'

as follows:

Fraction 1,

Fraction 2,

tr'ractÍon J,

n'raction l¡,

Fraction l,

tr'raction 6,

eluant

eluant

eLuant

eLuant

eluant

eluant

Iíght petrol;

lieþt petrol;

light petroL/ether ( 121) ;

light petrof ether ( l: t) ;

ether;

chLoncforrno

tr'raction 1o - Evaporation of the solvent gave a brigþt yellow resicìue

(tO mg). this was identi-fied. as mclianged 2r2t -ázod.ipher¡r}:nethan€¡ fr.P.

109o, alone or ad.mjxed. with an authentj-c sampl""to7

,Fra.ction 2. - An removal of the solvent a yellow oily resid.ue (ca. 10 *e)

was obtai¡red. which could not be induced. to crysta]-]jze. The ultravi-olet

spectrum (p"uk" ^t Ui5r 32Or LJO *Ð resembled. to that of the starting

materia]-o This compound. coul-d. not be id-entified.

Fractj-on J. - Evaporation of the solvent gave alx orange-yeLlovr so1id.

(0.: e). Recrysta,llizatj-on from cthanol gave dibenzopr!] [12] d-iazapin'-

11-one as orange-yellow need-Ies m.p. 19Bo al'one or admixed' wittr an

authentic ""*p1"10' (tcinafy supplied. by Dr. R.B" Johns, Universit¡' o¡

Melbourne), The ul.traviolet spectrum in etha:rol showed. peaks at 25Ot 325t

-1 16*

and. 440 mp" The irrf'rareC. spectrurn (CiÊfr) showed. a strong pak er 166J

."i1 (C=O) anÌ the mass spectrum of the compounö. shovred. a molecul-ar ion

(rde ZOB) (Analysis found: Cr 74"7; H¡ 4o1, N, 13,8o Calc. tor C"¡;gN20

C, 75.oi H, 5.8; Nr 13"5%).

tained.o Recrystal,lization from lÍght petrol yield.ed. yeJ-low needles of

2r2'-ðianínobenzophenone¡ il.po 13+-135o, alone or ad¡njx,ed witL¡ a:: auther:p

ti-c sample prepared- by the red.uotion of 2r2'-clinitrobenzophe.rorr"ltt (-aÉqn

Sfggg) o lts ir¡frared. spectrtrm showed peaks at JJ@, 33BO xA 16OZ crr-1

(ätl) arxl at 1650 cr-l (c=O) and. was id.entica-L witlr the spectn:,n of authen-

ti;c 2r2t -d.Íarninobenzophenoneo the mass spectrum showed a molecirlar ion

(rn/e 212) "

Fr:ecti-onfo - Evaporation of the soLvent gave a red.-bro'¡m resid.ue (O"t5g).

Recrystallization from carbon tetrachlorid,e afford-ed a reC.-brourn ,nic:'o-

crystalline so1id., m"p. 1Jl¡o (witi, d.ecomposition) o lts inf rared. spectrum

showed. peaks at JJOO, 3380, and. 163O "rf1 (lur)" It forned. an acetyl

d.erir¡ative on being refluxed. ïv:ith acetj-c arùryd.rid.e and, glacial acetic

acid, m.po 1950. The melt j-ng points of the compound. and. its acetyl d.eriva-

tive were in agreement with the melting point of 2r2r-d.iaminod.ipheriyÌ-

me'¡,Irarìe (ß4-l3yo)107 *a its acetyt d.erivatirre (n,"p. 198\.1o7 At'cenipts

to prepare a sal"icylid.ine derivative rre not successful.

-b'r¿l.ctLon bo - .þ,vapo::ation of the solvent gave a greeniskr-yellow residue

(0.1 g) vrhich on recrysta1lization from chlorrcform formed lemon-yelloIir

_1 19-

plates.r frop. 262o" Its infrared. spectrum showed. sharp peaks at 3330 a:;rð'

4.41615 crft (second.ary -lüf) and. at 1650 crri' (C.O)o f,he mass spectnm

showed. a molecul-ar ion (rde Zt0)(Ana1ysis found: Cr 73.1; H, 4"9; Ne

13.56" Calc. for 2r?t-Wdrazobenzophenone CrftONe0i C, 74"3i H, 4.8;

N, 1J.îi%) .

Attempts were nad.e to oxid.ise this compour:d by bubbling a:ir

through its solution in alkaline methar¡oI. UnchangeC. n'sterial v/as re-

covered. on remova.L of the solvent. Attempted' oxidation withr a-lkal"ine

sod.ium h¡rpobromite solution d.ecomposed. the compound artd no prrcd.uct could.

be isolated"

In a repeat e:çeriment under id.entical cond.itions althougþ all

the other compounds were formed. in compararole yi.eld. this last compound-

could. not be obta'ined..

In 9870 srrlphuric acj-d..

A solution of 2r2t -azod,ipherrylmethane (1 g) ín 9&ii' sulphuric

acid. (1OO mI) in a culture fl,ask was irradiated. in swrligþt' A slow

reaction proceeded and. when there vras no further apprecJø.b1e cha4ge (!

¿uy=) j¡ the uJ"traviolet spectrurn the reaction mixture v¿as diluted. rrith

ice-water (1 1) and. parti-ally neutralized.o A pale green solid. vrrhich

separated was collectea (O.g g) and. the acid.ic filtrate was basi-fied. witlr

sod.íum hydroxid.e. Extraction with benzene and evaporatj,on of the solvent

afford.ed. a brigþt yellow solid (O.J e) v¿hich when chromatographed on a

column of alumj¡ra yi-eld.ed. unchanged. 2r2t -a-odiphenyJrnethane ñ.P. âflC. mixed.

rnop. 1 l Ooo

-12ù,

the pale green solid.r'obtained. during parbial neutralization,

ryas soluble j-n ôilute aLlça1i and. couLd. be reprecipitated. by acid.ificationo

It was not soluble in ar5r organic solvents and could. only be recrystallized'

from concentrated hyd.rochlorJ-c acid. It d.id not melt up to 3600" Its

j,nfrared (nu¡of) showed a broad. ba:rd j.:: the region of J5OO- 27OA cr{1

(v¡ith two jJ.1-d.efined. peaks at, JJSO and, J2OO.*-1), and. absorptior"s at

't66, q{1 (c=o) t6l5 cr.l-l (¡ur) ana 805 ana 7J0 cm-1 (1 ,2 ¡F and. 1 ,2-

substituted. benzenes) o DLazotization of' this compor.ino and. coupling with

a-lkal,ine þnaphthol, a yellow $re was formed. rvhich turned red ín acid.

the compor¡¡rd- couLd. probably be a 5-substituted. sulphonic acid.

d.erivative of 2r2t-d.ianÉnobenzophenone (Anatysis.for:ndz C, JO"5Bö L, 1..61;

N, 8"92+; S, 10.r¡rro Clf,rZNZOf Ë20 requires C, JO"32; H¡ 4"5i N, 9.0J;

s, 10.33iá).

Irrad.iation of d.ibenzo þ,tJ ú '4 d-iazapin-1 1-one.

A solution of dibenzolgrg]fl;r2)dLazapin-11-one (o.l e) ín 1%

etha¡roIic sulphuric acid. (v:v) (1OO rnJ.) was irrad.i.ated. tvith sunligþt, vrhen

a slov¿ reaction proceededo Ïühen there was no fi-¡rther appreciable change

jn its ultraviolet spectrum (after ten d.ays) tkre ¡eaction mixture was

basified. with sod.ir.ur þyd.:roxid.e and. ethanol evaporated. offo the resid.ue

was extracted. with chloroforri, solvent evaporated. and the prod.uct chroma-

Logr.aplietl u¡¡ ¿r eolutlur of a-1u:ui¡r¿r using ether as eluant. thc fi-rst frao-

tj.ons on evaporation of the solvent yield.ed. unchanged. starting nqterial

(zS ^ù m,po and. mixed m"po 198e

"

-121-

tr'urther elution v¡ith ether yield.ed. a yellovr fraction v¡irlch on

evaporation of the solvent a¡d. recrystallization yield.ed. 2r2r-d.iarnino-

benzophenone (L5 rg) mopo and. ndxed. m.p, 1j+o " No other prod.ucts vrere

d.etecteå.

2 " 2t -D init robenz ophenone o

2r?l-Dínitrod.iphergrlmethane (t e) chror¡ric oxid.e (2"5 e) v¡ater

(Z.l *f)r md glacial acetic acid. (10 m]-) were refLuxed for' ó hours. ìIüleen

cooled. the mi:cture Tvas stir¡ed. into 100 m_r of vrater and. the precipi,uated.

soIid. collected. Recrystallization of the product (0.! g) from graci,aJ-

acetic acid. afforded.2r2t-d.j¡itn¡benzophenone a,s colourless need.Ies¡ hop.

lg8o (lit.1oB lggo¡.

2 . 2 | -DianLinobenzonhenone -

A rnixtuæ of 2r?t-d.initrobenzophenorr" (0.5 g), concentrateC.

lSrd.rnchloric acid. (¡O rf) and. tin metal was heated on a water*bath until

all the suspended. nj-tro compor,urd. òisso].ved.o '!,fhen cooled,, the reaction

nrixture was basified. with sod.ium hyd.rrrxid.e ar:d. extracted. with benzeneo

the resiclue obtai¡red. on evaporation of benzene vras recrystallized. from

light ¡ntzol. 2r2t -Dianinobenzophenone was obtained. as lemorrye|low

nee.rresr ilopo llho (lit.99 a!L-,ti5o).

sgcñgui{,{'¿ì{

1 o

-122-

Stobbe, Ho, Ber.<i-t"chem.Ges ", 1907, !Ê-t 3372.

?arker, Co0.¡ and Spoerri, PoE", I3!gg, 1950, ß, 6CA"

S,nrakr.r1a, Ào, (sjby$j@., 191+, Bþ., 90.

Lewis, G.No, I{agel , 1.T..r and. Lipkin, D., @t

lg4)t 62, 2973"

Buci<Ies, R.Eo, @o, 1955,27, 1040"

Coe, D.Go, Garnish, EolTo, Gale, M.Mo, and Îi¡rrnons, C).Jot

9@g-e!4-ItÈ", 1957 , 665 "

Hugelshofer, Po, Kal'voda , J . , and. Schaffner, Ko , þþ4Q!¡@þ!4. ,

1g60, Æ, 1322.

Stegemeyer, Ho, Ze[glll€orscþo, 1962, ïTb, 153"

Fonken, C.J.¡ Ohemo and. fnd.. , 1962, 1327.

Mallory, tr..3., Wood., C'.Sor Gorrd'on, JoTor Linquistr L.G., mð

Savitz, MoLor J.Amer.Chem"S.oc o, 1962, fu, 4361.

Moore¡ W.Mo, Morgan, D.D. r and. Stermitz, FoRo, J-4@$gfggo ¡

1963t þ., 8Zg"

Srj¡ri-vasan, Ro, a¡rd Power^s, Jro, J.G.r JéIgI1@$gg,", 1963,

þ., '1355

Mal}ory, F. Bo, Gordon, J.To¡ and Wood., C'.So¡ 44ggl¿þ,8"Þ99",

1963,95,828,

Mallory, F.B.r Tfood., C.S.r arrd. Gord'on, J'To, Jégqg.Cþ"mgþo,

196t+, &, t09+"

Tfood, C;.S., and. \{al}ory, F.Bo, J*9lg¡þo, 196+, ë.t 3575"

Kupchan, S.Iúor ani. \¡Iornser, H.C., @, "955, 359'

2o

2)o

4"

q)o

6o

7"

8o

9"

10"

12"

13"

1j+.

11.

15"

ióo

I lo

1Eo

19.

20"

21o

22"

-123-

Kharasch, N., Àlston, G.1., Irevris ¡ H.Bo, and. ìilolf , lV. t

Chemooorrmuno , 1955, 2+2'

S'argent, M.Vo, anC. f.i-mr'onsr CoJ., J.:-@,.t 196+, 55ü)"''

Load.er, C,Æ., Sargent, MJ., an<l Lj¡mons, C.Jo, .@!ry't

't96,, 127"

Bortol_us, P., Guzzo, G., and, Ga]-íazzo, Go, Ietrahed.ron Lett-ez'st

1966, 239.

Perkampus¡ H.Ho, and Senger, P., Ber.BunsenÉ"es physj'k' Cherno,

1g63, fr., 876"

Carruthers, \II.¡ and. Stevrarb, H'NolVI., Tetrahed-rrc.n Letters , 1965t

JOl.

Grellman, K.Ho, Sherman, G.Mo ¡ T¡inschitzr Ho, @,

1963,3å, 1881.

Lj-nsch-itz , H. , a¡rd. Grellmanr KoH., J.Amer.Chem'Soc" , 1964,

gi, 3o5"

Boiven,8,J., and. Eland.r J.HoDo, 3-þ;¿gq4gÞ}.t 1963, 2O2"

Lewis, GoEo, letrahed.ron Lgttezs t 1960r I9n-2, 12.

Leyris, G.E,rJs9.lg¡]hg!lo, 1960, .Æ., 2193"

Bad.ger, GLM. ¡ Ðrerve|, R'Jo ¡ and Lewisr G.Eo , 4llå@,

1963, 16, 1042"

Bad.ger, G.M., Dreler, R.J., an¿ Lewisr GoEo, A@s.,

1g6tÞ, !1, 1ö36"

Baclger, G.M"¡ Janr-leson, NoC.¡ and Levris, G.Eo¡ Allgldg1@"¡

196+, JJ, 1go"

Bad.ger, G.Mo, Drewer, R'.Jo¡ anô Lewis, G.Eo, $!.g|¡$4o,

1966, -þ., 6tr3"

2+"

ôz

ôq¿)o

26.

27"

28.

29"

30"

31"

32"

7Z

54"

7C.))o

36'

37"

zQ

39"

40.

lr1 o

+3"

U+"

)+5 "

46.

47o

l+8.

)+2"

-12\-

Jamieson, N.Co ¡ anC. T¿evris¡ G.E., Austo.T. Chem" t 1967t 20t 321 .

Qavar M.Por ard. Schlessingerr RoH.r Tetraherlron LetLer::, 't961+t

2109 "

lv1a11ory, $.Bor and. Víood., G,oS.r leirr¡.hecl.r'on Let'Le;:s , 1965, 2643.

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bUo

Qlo

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72"

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1719"

75"

/Þo

77"

78.

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80"

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B¿¡'"

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87"

gB.

89o

-1 2-7-

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90,

91o

92.

93"

9Lro

95"

96"

97'

9B'

oo

100 0

101 .

102"

10t.

I U¿Þo

291D.

-i2ù

1O5o lVilzbach, KoEó r and Kaplan, Lo, J.Amer'CheL'So9-' t 196L" ø,

1A6"

1O7 "

1 oBo

1O9 o

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111 "

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2307 "

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rs{0I&vJIT'ãn¿

Tetra.heil¡on Letters No.{9, pp. tTII-17Lt, 1964. Pergamon Preeg Lúil.Printeil in G¡eat Britein.

PHOIOCAT¡YSED CYCLTZATION OF 3NÍZAIANIT]NE

G.M. Bariger¡ C.P. Joshua ancl. G.E. I¡ewis

Departnent of Organic Cheroistry

Universlty of Adelaicle, South Aust¡al1a

(Recei.veit 19 0ctober 196{)

The f ornat ion of d.ibenzo[ c ¡!] phenantbr.irlin€ fton 1-naphtbaL-l r-

naphthylamÍne, rèc€ntLy ¡eported.l as the fl¡et exanpl-e of photooxidative

ring olosure of en a¡onatic Schiff,baee to a phenanthrldlne¡ proppts us

to ¡eco¡tl tbat benzalanifine (f) in solution in concentrated.sulphu¡io

acid ls photochenically converted. to a rcixtu¡e of phenantb¡ittiné (II) an.t

benzylaniline (III).

hvc6H5cH'Nc6H5 -iãffilsi + c6H5cËzNHc6E

A solution of benzalaniline (?6 ng.) in !8fr r¡1¿"rtt sulphurlc

ac:-d (1OO n1.) wae ir¡a,cllated for J2 hr wÍth a Philips 125 U nercury-quartz

lanp in a v¡ater-coolerl Pyrex photochenical reectot.2 Sototions in sulphurlc

acicl-wate¡ mlttu¡es coulal not be emptoyed ilue to rapirl lqrd.rolysls of the

Schiff base. lhe mirture, afte¡ ctilutlon with ice antl neut¡alizatíon r¡¡lth

soiliun \niroride, was eitracted with benzene. trVaporation of the solvent

yielcled. a b¡ov¡n-yellow gu¡ (58 ng. ) whfoh was ¡edissol-vecl in benzene ancl

obromatogrepheÈ on a oolu¡nn of sitica. Elution with a mixtu¡e of ethe¡

(tOÍ v:v) and. benzene caused benzylanillne to separete as the first band.

57rr

I rrrrI

nL2 No.49

(ye1J.ow fluorescence) fron the more stTongly ad-sorbecl phenantbrlttine

(blue-yellow fluorescence). the resitlue remaining aJter evaporation of

the flrst cbromatographic fraction was identlfied as benzylaniline by

lts conversion with, pheqylisothiocyanate to {-benzyl-NrNr-d.iphenylthio-

ca.¡baøitle (Z¡ re.) m.p. 1o?o; this was id.entical (mlxeil melting poínt

,antt infrarecl spectrun) n'ith the thioca¡banid.e prepared fxon an authentic

sample of benzytanillne. I¡ikewÍse the ¡esi¿lue (29 ^e.) n.p. 'lO3o trom

the seconcl fractlon was lclentlflecl as phenanthricline by conparison with

an authontl-c "arple.3

lhe quantun efflciency of the photochenical reå,otion of benzalaniline

unrle¡ these conditlons ls marked.ly lowe¡ than that of azobenzene in 22 N

sulphwic acld2 but the two reactions a¡e otherwise conpaiable.

ïn view of the fact that no phenanthrld.ine is fotmed- v¡hen benzal-

aniline is ir¡attíatetl 1n hexane4 and. that fornatÍon of benzyl-anlLlne

accompenies the cyclfzatlon of benzalaníline in concentratecl sulphr:ric

acid¡ thls Schiff base appears to be ¡nore closely lelate¿I in photochenical

behavior¡r to azobenøene ancl its d.erivatives2'5 thrn to the stilbenes.6

Azo compoundls when irrad.latecl u¡der strongly acíd.ic cond-itions give rise

to benzid.ine-rearrangement protlucts in ad.d.ition to benzofg]cinnolines2t5

but the conve¡sion of stilbene to phenanthrene appears not to be

acconpaniecl by formation of bibenzyl.? On the othe¡ hanalr the presence

of êlssolverl oxygen was shov¿n to be necessary for the photocatalysed

cycilizatioa of I -naphthal-l t-naphthylanine in benzene. I Dísproportion-

ation in this case does not therefo¡e play an apparentl-y significant

r01e.

Aoknowleclgnents. GratefuL aoknovleclgnent is mad-e of a grant frou

the Petrol-eum Resea¡ch tr\:nd ¿dni¡1strered by the Ane¡ican Cheml-cal SocietJ¡r

and. of assistance to one of us (C.f.,f.) fron CIBA of Ind.ia I¡td..

No. å9 17TJ

RE¡'M,ÐICEI

'1. M.P. Cava antt R.H. Sohlessinger, Tet¡ahed.¡on l¡etters, No. Jl, 2iO9

(tg6+).

2. G.M. Saclger, R.J. Drewe¡ anct G.E. Lewis, Auet.J.Chen. t É¡ 1042 1196J).

3. A. Plctet ancl II.J. Ankersnit, W, E, 3339 (i889).

4. P. Hugelshofer, J. Kalvocla ancl K. Sohaffner, Ilelv.Cblur.Acta¡ ¡[f,1322 (1960).

5. G.M. Sadger¡ R.J. I)¡ewer antt c.E. lewis, A¡st.J.Chen. t JJ¡ jO36 (196Ð.

6. RrE. Sucktes, J.Aner.Chem.Soc. t fh jO4O (lg>S); H. Stegemeyer, Z.

Natu¡fo¡sch., @, 153 (tg6z)i F.B. Marlory, J.T. Gordon ana e/s,

l/oorl, J.Aner.Chen.Soc., ø, 828 Ggel); I[.M. Moore, Ð.D. Morgan encl

F.R. Sternltz, ibiar., þ, Bz9 hgel); C.J. Ttørnons, i!igr., $¡, ztg6

(1 963 ).

7. Àccorcling to stegemeyer (þ. "it., 1962) no bíbenzyl can be d.etecterr

spectroscopically, but see also R. Srínivasan and. J.C. powers, J.Chen.

Phvs.¡ llr 5Bo (196j).

Badger, G. M., Joshua, C. P. & Lewis, G. E. (1965). Photochemical reactions

of azo compounds. V. Photochemical cyclodehydrogenations of Amino-,

Acetyl-, and Nitro-azobenzenes. Australian Journal of Chemistry, 18(10),

1639-1647.

NOTE:

This publication is included in the print copy

of the thesis held in the University of Adelaide Library.

It is also available online to authorised users at:

https://doi.org/10.1071/CH9651639