Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidation of L-phenylalanine by Ag(III) Periodate...

Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidationof L-phenylalanine by Ag(III) Periodate Complex in AqueousAlkaline Medium

Shekappa D. Lamani Æ Jyothi C. Abbar ÆSharanappa T. Nandibewoor

Received: 12 July 2009 / Accepted: 18 August 2009 / Published online: 10 September 2009

� Springer Science+Business Media, LLC 2009

Abstract The kinetics of oxidation of ruthenium(III)

(Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation

of L-phenylalanine (L-Pal) by diperiodatoargentate(III)

(DPA) in aqueous alkaline medium at 27 �C and a constant

ionic strength of 0.25 mol dm-3 was studied spectropho-

tometrically. The involvement of free radicals was

observed in the reactions. The reaction between DPA

and L-Pal in alkaline medium exhibits stoichiometry as

[L-Pal]:[DPA] = 1:1. The reaction is of first order in

[Os(VIII)], [Ru(III)] and [DPA] and has negative fractional

order in [IO4-]. It has less than unit order in [L-Pal] and

[OH-]. However, the order in [L-Pal] and [OH-] changes

from first order to zero order as their concentrations

increase. The main oxidation products were identified by

spot test and spectral studies. The probable mechanisms

were proposed and discussed. The catalytic constant (Kc)

was also calculated for Os(VIII) and Ru(III) catalysis at

different temperatures. The activation parameters with

respect to slow step of the mechanisms were computed and

discussed and thermodynamic quantities were also calcu-

lated. It has been observed that the catalytic efficiency for

the present reaction is in the order of Os(VIII) [ Ru(III).

The active species of catalyst and oxidant have been

identified.

Keywords Kinetics � Oxidation � L-phenylalanine �Diperiodatoargantate(III) � Osmium(VIII) catalysis �Ruthenium(III) catalysis

1 Introduction

The oxidation of amino acids is of interest as the oxidation

products differ for different oxidants [1, 2]. Thus, the study

of amino acids becomes important because of their bio-

logical significance and selectivity towards the oxidants.

Amino acids have been oxidized by variety of oxidizing

agents [3]. L-phenylalanine (L-Pal) is an essential amino

acid. It forms active sites of enzyme and helps in main-

taining their proper confirmation by keeping them in proper

ionic states. So oxidation of L-Pal may help in under-

standing some aspects of enzyme kinetics. L-phenylalanine

supplementation helps in the suppression of the pain and

aid weight loss through the suppression of appetite. It is

converted in to tyrosine, which is precursor to dopamine

levels, have a definite function in sexual desire.

Diperiodatoargentate(III) (DPA) is a powerful oxidising

agent in alkaline medium with the reduction potential [4]

1.74 V. It is widely used as a volumetric reagent for the

determination of various organic and inorganic species [5].

Jayaprakash Rao and other researchers have studied DPA

as an oxidizing agent for the kinetics of oxidation of some

organic substrates [6]. They normally found that order with

respect to both oxidant and substrate was unity and [OH-]

was found to enhance the rate of reaction. It was also

observed that they did not arrive at the possible active

species of DPA in alkali, and on the other hand they pro-

posed mechanisms by generalizing the DPA as

[Ag(HL)L](x?1). However, Kumar et al. [7, 8] put an effort

to give an evidence for the reactive form of DPA in large

scale of alkaline pH. Ag(III) complexes can be stabilized in

alkaline medium by periodate or tellurate ions [9, 10].

When the silver(III) species are involved, it would be

interesting to know which of the species is the active

oxidant. In the present investigation, we have obtained the

S. D. Lamani � J. C. Abbar � S. T. Nandibewoor (&)

Department of Chemistry, Karnatak University,

Dharwad 580 003, India

e-mail: [email protected]

123

Catal Lett (2009) 133:142–155

DOI 10.1007/s10562-009-0134-5

evidence for the reactive species for DPA in alkaline

medium.

Transition metals are known to catalyse many oxida-

tion–reduction reactions since they involve multiple oxi-

dation states. In recent years the use of transition metal ions

such as osmium, ruthenium, palladium, manganese, chro-

mium, iridium, either alone or as binary mixtures, as cat-

alysts in various redox processes has attracted considerable

interest [11]. Although the mechanism of catalysis depends

on the nature of the substrate, the oxidant and experimental

conditions, it has been shown that metal ions act as cata-

lysts by one of these different paths such as the formation

of complexes with reactants or oxidation of the substrate

itself or through the formation of free radicals. Osmium

(VIII) (Os(VIII)) and ruthenium(III) (Ru(III)) catalysis in

redox reactions involves different degrees of complexity,

due to the formation of different intermediate complexes

and different oxidation states of osmium/ruthenium, etc.

The uncatalysed reaction of oxidation of L-Pal by DPA has

been studied [12]. We have observed that Os(VIII) and

Ru(III) catalyzes the oxidation of L-Pal by DPA in alkaline

medium in micro amounts. In order to understand the

active species of oxidant and catalyst, and to propose the

appropriate mechanism, the title reaction has been inves-

tigated in detail. An understanding of the mechanism

allows the chemistry to be interpreted, understood and

predicted.

2 Experimental Section

2.1 Chemicals and Solutions

All reagents were of analytical reagent grade and Millipore

water was used throughout the work. A solution of

L-phenylalanine (HiMedia Laboratories) was prepared by

dissolving an appropriate amount of recrystallised sample

in Millipore water. The purity of L-Pal was checked by its

m.p. 273 �C [Lit.m.p.275 �C]. The IR spectrum agreed

with literature. The required concentration of L-Pal was

used from its stock solution. The Os(VIII) solution was

prepared by dissolving OsO4 (Jonshon Matthey) in

0.50 mol dm-3 in NaOH. The concentration was ascer-

tained [13] by determining the unreacted [Fe(CN)6]4- with

standard Ce(IV) solution in an acidic medium. A standard

stock solution of Ru(III) was prepared by dissolving RuCl3(S.D. Fine Chemicals) in 0.20 mol dm-3 HCl. The con-

centration was determined [14, 15] by EDTA titration.

KNO3 and KOH (BDH) were used to maintain the ionic

strength and alkalinity of the reaction, respectively. An

aqueous solution of AgNO3 was used to study the product

effect, Ag(I). A stock solution of IO4- was prepared by

dissolving a known weight of KIO4 (Riedel-de-Hean) in

hot water and used after keeping for 24 h to attain the

equilibrium. Its concentration was ascertained iodometri-

cally [16], at neutral pH maintained using phosphate buf-

fer. The pH of the medium in the solution was measured by

ELICO (L1613) pH meter.

2.2 Instruments Used

(a) For kinetic measurements, a CARY 50 Bio UV–vis

Spectrophotometer (Varian, Victoria-3170, Australia)

was used.

(b) GC-mass data were obtained on a 17A Shimadzu gas

chromatography with a QP-5050A Shimadzu mass

spectrometer

(c) Nicollet 5700-FT-IR spectrometer (Thermo, USA.)

2.3 Preparation of DPA

DPA was prepared by oxidizing Ag(I) in presence of KIO4

as described elsewhere [17]. The complex was character-

ized from its UV spectrum, which exhibited three peaks at

216, 255 and 362 nm. These spectral features were iden-

tical to those reported earlier for DPA [18]. The magnetic

moment study revealed that the complex was diamagnetic.

The compound prepared was analyzed [19] for silver and

periodate by acidifying a solution of the material with HCl,

recovering and weighing the AgCl for Ag and titrating the

iodine liberated when excess KI was added to the filtrate

for IO4-. The aqueous solution of DPA was used for the

required [DPA] in the reaction mixture. During the kinetics

a constant concentration viz. 1.0 9 10-5 mol dm-3 of

KIO4 was used throughout the study unless otherwise sta-

ted. Thus, the possibility of oxidation of L-Pal by periodate

was tested and found that there was no significant inter-

ference due to KIO4 under experimental condition. The

total concentrations of periodate and OH- was calculated

by considering the amount present in the DPA solution and

that additionally added. Kinetic runs were also carried out

in N2 atmosphere in order to understand the effect of dis-

solved oxygen on the rate of the reaction. No significant

difference in the results was obtained under a N2 atmo-

sphere and in the presence of air. In view of the ubiquitous

contamination of carbonate in the basic medium, the effect

of carbonate was also studied. Added carbonate had no

effect on the reaction rates.

2.4 Instrumentation and Kinetic Measurements

All kinetics measurements were performed on a Varian

CARY 50 Bio UV–vis Spectrophotometer. The kinetics

was followed under pseudo-first order condition where

[L-Pal] [ [DPA] in catalysed reactions at 27.0 ± 0.1 �C,

Mechanistic Aspects of Os(VIII)/Ru(III) 143

123

unless specified. The reaction was initiated by mixing DPA

with the L-Pal solution which also contained required

concentrations of Os(VIII) or Ru(III), KNO3, KOH and

KIO4. The progress of the reaction was monitored spec-

trophotometrically at 360 nm (i.e., decrease in absorbance

due to DPA with the molar absorbancy index, ‘e’ to be

13,900 ± 100 dm3 mol-1 cm-1, literature value being

13,892 dm3 mol-1 cm-1, in both catalysed reactions),

which is the maximum absorption wavelength of DPA. The

spectral changes during the chemical reaction for the

standard condition at 300 K are given in Fig. 1. It was

verified that there was almost no interference from other

species in the reaction mixture at this wavelength.

The pseudo-first order rate constants, ‘kC’, were

determined from the log (absorbance) versus time plots.

The plots were linear up to 85% completion of reaction

under the range of [OH-] used. The orders for various

species were determined from the slopes of plots of log kC

versus respective concentration of species except for

[DPA] in which non-variation of ‘kC’ was observed as

expected to the reaction condition. The rate constants

were reproducible to within ±5%. Regression analysis of

experimental data to obtain regression coefficient r and

the standard deviation S, of points from the regression

line, was performed with the Microsoft office Excel-2003

programme.

3 Results

3.1 Stoichiometry and Product Analysis

Different sets of reaction mixtures containing varying

ratios of DPA to L-Pal in the presence of constant amount

of OH-, KNO3 and KIO4 and Os(VIII)/Ru(III) catalyst

were kept for 2 h in a closed vessel under nitrogen atmo-

sphere. The remaining concentration of DPA was estimated

by spectrophotometrically at 360 nm. The results indicated

a 1:1 stoichiometry as given in Eq. 1.

The main oxidation products were identified as aldehyde

(phenylacetaldehyde), by a spot test [19]. Ammonia was

identified by Nessler’s reagent and CO2 was qualitatively

detected by bubbling N2 gas through the acidified reaction

mixture and passing a liberated gas through a tube con-

taining limewater. The aldehyde was confirmed by pre-

paring its 2, 4-DNP derivative. The nature of phenyl

acetaldehyde was confirmed by its IR spectrum which

showed a C=O at 1,630 cm-1 indicating the presence of

aldehydic C=O and C–H stretching at 1,745 cm-1. Further,

phenylacetaldehyde was subjected to GC-mass spectral

analysis. GC-mass data were obtained on a 17A shimadzu

gas chromatography with a QP-5050A Shimadzu mass

spectrometer using the EI ionization technique. The mass

spectrum showed a molecular ion peak at 119 amu con-

firming the presence of phenylacetaldehyde product

(Fig. 2). All other peaks observed in GC–MS can be

interpreted in accordance with the observed structure of

phenylacetaldehyde. The formation of Ag? in solution was

detected by adding KCl solution to the reaction mixture,

CH2 CHO[Ag(H2IO6)(H2O)2]+ + H2IO6

(1)

3-

+ + NH4 Ag(I)+

Ru(III)/Os(VIII)CH2

NH2

COOCH

CO2 H2O+

Fig. 1 Spectroscopic changes occurring in the Os(VIII) catalysed

oxidation of L-phenylalanine by diperiodatoargentate(III) at 27 �C,

[DPA] = 5.0 9 10-5, [L-Pal] = 5.0 9 10-4, [Os(VIII)] = 8.0 9

10-7, [OH-] = 0.05 and I = 0.25 mol dm-3 with scanning time of:

(1) 0.5, (2) 1.0, (3) 1.5, (4) 2.0, (5) 2.5 and (6) 3.0 minFig. 2 GC-mass spectrum of phenylacetaldehyde with its molecular

ion peak at 119 amu

144 S. D. Lamani et al.

123

which produced white turbidity due to formation of AgCl.

It was observed that phenyl acetaldehyde did not undergo

further oxidation under the present kinetic conditions.

3.2 Reaction Orders

As the diperiodatoargantate(III) oxidation of L-phenylala-

nine in alkaline medium proceeds with a measurable rate in

the absence of ruthenium(III) or osmium(VIII), the cata-

lysed reaction is understood to occur in parallel paths with

contributions from both the catalysed and uncatalysed

paths. Thus the total rate constant (kT) is equal to the sum

of the rate constants of the catalysed (kC) and uncatalysed

(kU) reactions, so kC = kT - kU. Hence, the reaction orders

have been determined from the slopes of log kC versus log

(concentration) plots by varying the concentrations of

L-Pal, alkali, periodate and Ru(III) or Os(VIII) catalyst in

turn while keeping all other concentrations and conditions

constant.

3.3 Evaluation of Pseudo-first Order Rate Constants

The oxidant [DPA] was varied in the range of 1.0 9 10-5

to 1.0 9 10-4 mol dm-3 at 27 �C for both the catalysts

while keeping other reactant concentrations and condi-

tions constant. The fairly constant pseudo-first order rate

constants, kC, indicate that the order with respect to

[DPA] was unity (Tables 1 and 2). This was also con-

firmed by linearity of the plots of log (absorbance) ver-

sus time (r [ 0.999, S B 0.04) upto 85% completion of

the reaction.

3.4 The Dependence of Rate on the Concentration

of L-phenylalanine

The effect of L-Pal was studied in the range of

3.0 9 10-4 to 3.0 9 10-3 mol dm-3 at 27 �C while

keeping other reactant concentrations conditions constant

in the presence of both the catalysts. The kC values

Table 1 Effect of [DPA], [L-Pal], [IO4], [OH-] and [Ru(III)] on the ruthenium(III) catalysed oxidation of L-phenylalanine by DPA in aqueous

alkaline medium at 25 �C, I = 0.25 mol dm-3

[DPA] 9 105

(mol dm-3)

[L-pal] 9 104

(mol dm-3)

[IO4] 9 105

(mol dm-3)

[OH-] 9 102

(mol dm-3)

[Ru(III)] 9 106

(mol dm-3)

kT 9 102

(s-1)

kU 9 103

(s-1)

kC 9 102 (s-1)

Found Calculated

1.0 5.0 1.0 5.0 5.0 1.8 4.6 1.3 1.8

3.0 5.0 1.0 5.0 5.0 1.7 4.5 1.3 1.8

5.0 5.0 1.0 5.0 5.0 1.8 4.7 1.3 1.8

8.0 5.0 1.0 5.0 5.0 1.7 4.6 1.3 1.8

10.0 5.0 1.0 5.0 5.0 1.9 4.4 1.5 1.8

5.0 3.0 1.0 5.0 5.0 1.3 4.0 0.95 0.89

5.0 5.0 1.0 5.0 5.0 1.8 4.6 1.3 1.4

5.0 8.0 1.0 5.0 5.0 2.6 5.1 2.1 2.1

5.0 10.0 1.0 5.0 5.0 3.5 6.0 2.8 2.9

5.0 20.0 1.0 5.0 5.0 5.2 7.0 4.1 4.1

5.0 30.0 1.0 5.0 5.0 6.4 8.0 5.5 5.3

5.0 5.0 0.5 5.0 5.0 2.4 6.9 1.7 1.6

5.0 5.0 0.8 5.0 5.0 2.0 5.6 1.5 1.5

5.0 5.0 1.0 5.0 5.0 1.8 4.6 1.3 1.4

5.0 5.0 3.0 5.0 5.0 1.2 3.5 0.85 0.94

5.0 5.0 5.0 5.0 5.0 0.98 2.7 0.71 0.70

5.0 5.0 1.0 1.0 5.0 0.96 2.0 0.76 0.74

5.0 5.0 1.0 3.0 5.0 1.6 4.0 1.2 1.2

5.0 5.0 1.0 5.0 5.0 1.8 4.6 1.3 1.4

5.0 5.0 1.0 8.0 5.0 2.1 5.1 1.6 1.6

5.0 5.0 1.0 10.0 5.0 2.4 5.5 1.8 1.7

5.0 5.0 1.0 5.0 0.1 0.99 4.6 0.53 0.56

5.0 5.0 1.0 5.0 0.3 1.2 4.6 0.75 0.8

5.0 5.0 1.0 5.0 0.5 1.8 4.6 1.3 1.4

5.0 5.0 1.0 5.0 0.8 3.7 4.6 3.2 3.5

5.0 5.0 1.0 5.0 1.0 4.6 4.6 4.1 4.2


123

increased with increase in [L-Pal]. The order with respect

to [L-Pal] was less than unity (Ru(III) catalysed Table 1

and Os(VIII) catalysed Table 2) (r C 0.9847, S B 0.006).

However the order in [L-Pal] changes from first to zero

order as [L-Pal] varies.


of OH-

The effect of alkali was studied in the range of 0.01–

0.10 mol dm-3 at 27 �C and constant concentrations of

DPA, L-Pal, IO4-, KNO3 and Ru(III)/Os(VIII) catalysts.

The rate constants increased with increase in [alkali] and

the order was found to be less than unity (Ru(III) catalysed

Table 1 and Os(VIII) catalysed Table 2) (r C 0.9846,

S B 0.0045). The order in [OH-] also changes from first to

zero order as [OH-] varies.


of IO4-

The effect of periodate was studied in the range of

5.0 9 10-6 to 5.0 9 10-5 mol dm-3 at 27 �C, constant

concentrations of DPA, L-Pal, OH-, KNO3 and Ru(III)/

Os(VIII) catalysts. The experimental results indicated that

kC values decreased with increase in the [IO4-]. The order

with respect to IO4- was negative fractional (Table 1)

(r C 0.9982, S B 0.003).

3.7 Effect of [Ru(III)] or [Os(VIII)]

The ruthenium(III) concentrations were varied from

1.0 9 10-6 to 1.0 9 10-5 mol dm-3 and osmium(VIII)

were varied from 5 9 10-7 to 5 9 10-6 mol dm-3 at

27 �C and at constant concentrations of DPA, L-Pal, alkali

and ionic strength. The order in [Ru(III)] and [Os(VIII)]

Table 2 Effect of [DPA], [L-Pal], [IO4], [OH-] and [Os(VIII)] on the osmium(VIII) catalysed oxidation of L-phenylalanine by DPA in alkaline

medium at 25 �C, I = 0.25 mol dm-3

[DPA] 9 105

(mol dm-3)

[L-Pal] 9 104

(mol dm-3)

[IO4] 9 105

(mol dm-3)

[OH-] 9 102

(mol dm-3)

[Os(VIII)] 9 107

(mol dm-3)

kT 9 102

(s-1)

kU 9 103

(s-1)

kC 9 102 (s-1)

Found Calculated

1.0 5.0 1.0 5.0 8.0 2.9 4.6 2.5 2.2

3.0 5.0 1.0 5.0 8.0 2.8 4.5 2.4 2.2

5.0 5.0 1.0 5.0 8.0 2.8 4.7 2.5 2.2

8.0 5.0 1.0 5.0 8.0 2.8 4.6 2.3 2.2

10.0 5.0 1.0 5.0 8.0 2.9 4.4 2.5 2.2

5.0 3.0 1.0 5.0 8.0 1.9 4.0 1.5 1.5

5.0 5.0 1.0 5.0 8.0 2.8 4.6 2.3 2.2

5.0 8.0 1.0 5.0 8.0 3.5 5.1 3.0 3.1

5.0 10.0 1.0 5.0 8.0 4.1 6.0 3.4 3.5

5.0 20.0 1.0 5.0 8.0 5.9 7.0 5.1 4.9

5.0 30.0 1.0 5.0 8.0 6.8 8.0 6.0 5.7

5.0 5.0 0.5 5.0 8.0 3.8 6.9 3.1 3.1

5.0 5.0 0.8 5.0 8.0 3.2 5.6 2.6 2.6

5.0 5.0 1.0 5.0 8.0 2.8 4.6 2.3 2.2

5.0 5.0 3.0 5.0 8.0 1.3 3.5 0.98 0.98

5.0 5.0 5.0 5.0 8.0 0.96 2.7 0.69 0.69

5.0 5.0 1.0 1.0 8.0 0.97 2.0 0.71 0.70

5.0 5.0 1.0 3.0 8.0 2.1 4.0 1.6 1.6

5.0 5.0 1.0 5.0 8.0 2.8 4.6 2.3 2.2

5.0 5.0 1.0 8.0 8.0 3.3 5.1 2.7 2.8

5.0 5.0 1.0 10.0 8.0 3.6 5.5 3.0 3.1

5.0 5.0 1.0 5.0 5.0 1.5 4.6 1.0 1.1

5.0 5.0 1.0 5.0 8.0 2.8 4.6 2.3 2.2

5.0 5.0 1.0 5.0 10 3.6 4.6 3.1 3.5

5.0 5.0 1.0 5.0 30 8.3 4.6 8.3 8.5

5.0 5.0 1.0 5.0 50 13.1 4.6 12.6 12.7


123

was found to be unity from the linearity of the plots of kC

versus [Ru(III)] and kC vs. [Os(VIII)].

3.8 The Dependence of Rate on Ionic Strength (I) and

Dielectric Constant (D)

The addition of KNO3, to increase the ionic strength of the

reaction, increased the rate of reaction at constant [DPA],

[L-Pal], [OH-], [IO4-] and Ru(III) in (Fig. 3) and Os(VIII)

in (Fig. 4). The plots of log kC versus HI was found to be

linear with positive slope.

The dielectric constant of the medium, ‘D’ was varied

by varying the t-butyl alcohol and water percentage. The D

values were calculated from the equation: D = Dw

Vw ? DB VB, where Dw and DB are dielectric constants of

pure water and t-butyl alcohol, respectively, in the total

mixture. The decrease in the dielectric constant of the

reaction medium increases the rate and the plot of log kC

versus 1/D was found to be linear with negative slope for

Ru(III) (Fig. 3) and for Os(VIII) (Fig. 4).

3.9 Effect of Initially Added Products

Initially added products Ag(I) and aldehyde did not have

any significant effect on the rate of reaction.

3.10 Polymerization Study

The intervention of the free radicals was examined as

follows. The reaction mixture, to which known quantity of

acrylonitrile scavenger has been added initially, was kept

in an inert atmosphere for 6 h. Upon diluting the reaction

mixture with methanol, precipitate resulted, suggesting

there is participation of free radicals in the reaction.

3.11 Effect of Temperature

The influence of temperature on the rate of reaction was

studied at 22, 27, 32 and 37 �C. The rate constants, (kC), of

the slow step of Schemes 1 and 2 was obtained from the

slopes and the intercepts of the plots of [Ru(III)]/kC or

[Os(VIII)]/kC vs. 1/[L-pal] at four different temperatures.

The values are given in Tables 1 and 2. The activation

parameters for the rate determining step were obtained by

the least square method of plot of log kC vs. 1/T and are

presented in Tables 3 and 4.

3.12 Catalytic Activity

It has been pointed out by Moelwyn-Hughes [20] that in

the presence of catalyst, the uncatalysed and catalysed

reactions proceed simultaneously, so that,

kT ¼ kU þ KC½catalyst]x ð2Þ

Here kT is the observed pseudo-first order rate constant in

the presence of Ru(III)/Os(VIII) catalyst, kU, the pseudo

first-order rate constant for the uncatalysed, KC the

catalytic constant and ‘x’ the order of the reaction with

respect to Ru(III)/Os(VIII). In the present investigations, x

values for the standard run were found to be unity for

Ru(III)/Os(VIII). Then the value of KC is calculated using

the equation,

KC ¼kT � kU

½catalyst]x ¼kC

½catalyst]x where; kT � kU ¼ kCð Þ

ð3Þ

The values of KC were evaluated for both the catalysts at

different temperatures. Further, plots of log KC versus 1/T

were linear and the values of energy of activation and other

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.2 0.4 0.6 0.8

0

0.5

1

1.5

2

2.5

3

1.21.41.61.8

4 +

logk

C

I1/2

4 +

logk

C

1/D X 10-2

Fig. 3 Effect of ionic strength and dielectric constant of the medium

on Ru(III)-catalysed oxidation of L-phenylalanine by diperiodatoarg-

entate(III) at 27 �C

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.2 0.4 0.6 0.8

0

0.8

1.6

2.4

3.2

1.21.41.61.8

4 +

logk

C

1/D X 10-2

I1/2

4 +

logk

C

Fig. 4 Effect of ionic strength and dielectric constant of the Os(VIII)

catalysed oxidation of L-phenylalanine by diperiodatoargentate(III) at

27 �C


123

activation parameters with reference to catalyst were

computed. These results are summarized in Table 5. The

value of KC for Ru(III) is 2.7 9 103 at 300 K and the

values of KC for Os(VIII) is 2.9 9 104 at 300 K.

4 Discussion

Due to strong versatile nature of two electrons oxidant, the

kinetics of oxidation of various organic and inorganic

substrates has been studied by Ag(III) species. The litera-

ture survey [17] reveals that the water soluble diperiodat-

oargentate(III) (DPA) has a formula [Ag(IO6)2]7- with

dsp2 configuration of square planar structure, similar to

diperiodatocopper(III) complex with two bidentate ligands,

periodate to form a planar molecule. In the alkaline med-

ium, the dissociative equilibria (4–6) of the IO4- were

detected and the corresponding equilibrium constants were

determined at 298.2 K by Aveston [21].

2IO�4 þ 2OH� � H2I2O4�10 logb1 ¼ 15:05 ð4Þ

IO�4 þ OH� þ H2O� H3IO2�6 logb2 ¼ 6:21 ð5Þ

IO�4 þ 2OH� � H2IO3�6 logb3 ¼ 8:67 ð6Þ

The distribution of all species of periodate in aqueous

alkaline solution can be calculated from equilibria (4–6). In

the [OH-] range used in this work the amount of dimer

(H2I2O104-) and IO4

- species of periodate can be neglected.

The main species of periodate are H2IO63- and H3IO6

2-,

which are consistent with the result calculated from

Crouthamel’s data [22]. Hence DPA could be as [Ag(H3

IO6)2]- or [Ag(H2IO6)2]3- in alkaline medium. Therefore,

under the present condition, diperiodatoargentate(III), may

be depicted as [Ag(H3IO6)2]-. The similar speciation of

H+ + OH-fast

H2O

CH2CH

NH2

Ag(OH)++ CH2CHO

NH3 Ag(I)+ +fast

.

[Ag(H3IO6)2]- + OH-

K1

[Ag(H3IO6)(H2IO6)]2- + H2O

HCO3-CO2 OH-+

fast

[Ag(H3IO6)(H2IO6)]2- 2H2O+

K2[Ag(H2IO6)(H2O)2] [H3IO6]

2-+

[OsO4(OH)2]2-+CH2 CH

NH2

COOComplex(C2)

K4

CO2 H++ ++ [OsO4(OH)2]2-H2O +

k2

+++Complex(C2) [Ag(H2IO6)(H2O)2] H2IO63-Ag(OH)+

slow

CH2 CH

NH2

Scheme 2

H+ + OH-fast

H2O

CH2CH

NH2

Ag(OH)++ CH2CHO

NH3 Ag(I)+ +fast

.

+CH2 CH

NH2

COO[Ru(H2O)5OH]2+

Complex(C1)K3

fastHCO3

-CO2 OH-+

CH2 CH

NH2

k+++Complex(C1) [Ag(H2IO6)(H2O)2]

[Ru(H2O)5(OH)]2+

H2IO63-Ag(OH)+

H++ ++

slow

CO2 H2O+

1

Scheme 1


123

periodate in alkali was proposed [23] for diperioda-

tonickelate(IV).

It is known that L-phenylalanine exists in the form of

Zwitterion [24] in aqueous alkaline medium. In highly

acidic medium, it exists in the protonated form, where as in

highly basic medium it is in the fully deprotonated form

[24] as

C6H5 � CH2 � NH2 � CH� COO�

4.1 Mechanism of Ru(III) Catalysed Reaction

It is interesting to identify the probable ruthenium(III)

chloride species in alkaline media. The added chloride had

no effect on the rate of reaction. Electronic spectral studies

[23] have confirmed that ruthenium chloride exists in the

hydrated form as [Ru(H2O)5OH]2?. In the present study (at

pH 13.3), it is quite probable that for [Ru(III)(OH)x]3-x, the

Table 4 Thermodynamic activation parameters for the osmium(VIII)

catalysed oxidation of L-phenylalanine by DPA in aqueous alkaline

medium with respect to the slow step of Scheme 1

Temperature (K) k2 9 104 dm3 mol-1 s-1

(a)Effect of temperature

295 2.2

300 2.4

305 2.6

310 2.9

Parameter Value

(b) Activation parameters

Ea (kJ mol-1) 13.0 ± 2.5

DH# (kJ mol-1) 10.5 ± 1.5

DS# (JK-1 mol-1) -107 ± 2.0

DG# (kJ mol-1) 42.6 ± 3.0

log A 7.6 ± 0.3

Temperature (K) K1

(dm3 mol-1)

K2 9 104

(mol dm-3)

K4 9 10-2

(dm3 mol-1)

(c) Effect of temperature on K1, K2 and K4 for the osmium(VIII)

catalysed oxidation of L-phenylalanine by diperiodatoargentate(III)

in aqueous alkaline medium

295 0.4 5.5 6.6

300 0.6 2.3 7.5

305 1.1 1.8 8.6

310 1.8 1.0 9.8

Thermodynamic

quantities

Values

from K1

Values

from K2

Values

from K4

(d) Thermodynamic quantities using K1, K2 and K3

DH (kJ mol-1) 78 -81 20

DS (JK-1 mol-1) 259 -340 121

DG (kJ mol-1) 2.2 21.5 -16.8

Table 5 Values of catalytic constant (KC) at different temperatures

and activation parameters calculated using KC values for Ru(III)/

Os(VIII) catalysed reaction

Temperature (K) KC 9 10-3 Ru(III) KC 9 10-4 Os(VIII)

295 1.9 2.0

300 2.7 2.9

305 4.0 3.4

310 5.3 4.9

Ea (kJ mol-1) 51.3 42.4

DH# (kJ mol-1) 48.8 40.0

DS# (JK-1 mol-1) 14.5 -25.5

DG# (kJ mol-1) 52.1 47.7

log A 12.4 11.8

Table 3 Thermodynamic activation parameters for the ruthe-

nium(III) catalysed oxidation of L-phenylalanine by DPA in aqueous

alkaline medium with respect to the slow step of Scheme 1

Temperature (K) k1 9 104 dm3 mol-1 s-1

(a) Effect of temperature

295 2.2

300 3.1

305 4.0

310 4.8

Parameter Value

(b) Activation parameters

Ea (kJ mol-1) 38.8 ± 2.5

DH# (kJ mol-1) 36.8 ± 1.5

DS# (JK-1 mol-1) -38.5 ± 2.0

DG# (kJ mol-1) 47.5 ± 3.0

log A 11.2 ± 0.3

Temperature (K) K1

(dm3 mol-1)

K2 9 104

(mol dm-3)

K3 9 10-2

(dm3 mol-1)

(c) Effect of temperature on K1, K2 and K3 for the ruthenium(III)

catalysed oxidation of L-phenylalanine by diperiodatoargentate(III)

in aqueous alkaline medium

295 0.7 8.4 1.2

300 0.9 6.4 2.7

305 1.3 3.9 3.7

310 2.2 2.4 4.6

Thermodynamic

quantities

Values

from K1

Values

from K2

Values

from K3

(d) Thermodynamic quantities using K1, K2 and K3

DH (kJ mol-1) 55 -64 66

DS (JK-1 mol-1) 185 -277 265

DG (kJ mol-1) -2.0 19.5 -14.1


123

x valves would always be less than six because there are no

definite reports of any hexahydroxy ruthenium species. The

remainder of the coordination sphere would be filled by

water molecules. Hence, the condition employed, e.g.,

[OH-] � [Ru(III)], ruthenium(III) is mostly present as the

monomerichydroxylated species, [Ru(H2O)5OH]2? [25].

In the prior equilibrium step 1, the OH- deprotonates

the DPA to give a deprotonated diperiodatoargentate(III);

in the second step displacement of a ligand, periodate takes

place to give free periodate which is evidenced by decrease

in the rate with increase in [IO4-] (Table 1). It may be

expected that lower Ag(III) periodate species such as MPA

is more important active species in the reaction than DPA.

The inverse fractional order in [H3IO62-] might also be due

to this reason. In the pre rate determining stage, the

hydroxylated species of Ru(III) combines with a molecule

of L-Pal to give an intermediate complex, which further

reacts with one mole of MPA in rate determining step to

give a free radical derived from L-Pal with the regeneration

of the ruthenium(III) catalyst. This free radicals from the

L-Pal further reacts with another molecule of MPA species

in a fast step to give the products as given in Scheme 1.

The probable structure of the complex (C1) is given

below;

Spectroscopic evidence for the complex formation

between Ru(III) and L-Pal was obtained from UV–vis

spectra of L-Pal (5.0 9 10-4), Ru(VIII) (5.0 9 10-6,

[OH-] = 0.05 mol dm-3) and a mixture of both. A

hypsochromic shift of about 5 nm from 234 to 229 nm

in the spectra of Ru(III) was observed. The Michaelis–

Menten plot proved the complex formation between

catalyst and substrate, which explains less than unit order

in [L-Pal]. Such a complex between a catalyst and

substrate has also been observed in other studies [26].

From Scheme 1, the rate law (8) can be derived.

Equation 8 can be rearranged to Eq. 9, which is suitable for

verification.

½RuðIIIÞ�kC

¼ ½H3IO2�6 �

k1K1K2K3½L-Pal] [OH�� þ½H3IO2�

6 �k1K2K3½L-Pal]

þ 1

k1K3½L-Pal]þ ½H3IO2�

6 �k1K1K2½OH�� þ

½H3IO2�6 �

k1K2

þ 1

k1

ð9Þ

According to Eq. 9, other conditions being constant, plots

of [Ru(III)]/kC vs. 1/[L-Pal], 1/[OH-] and [H3IO62-] should

be linear and are found to be (Fig. 5a–c). The slopes and

intercepts of such plots, lead to the values of K1, K2, K3 and

k1 (Table 3) calculated as (0.93 ± 0.05) dm3 mol-1, (6.4

± 0.2) 9 10-4 mol dm-3, (2.7 ± 0.1) 9 102 dm3 mol-1,

(3.1 ± 0.2) 9 104 dm3 mol-1 s-1. The value of K1 is in

good agreement with the literature [27] and the value of K2 is

good agreement with the literature [28]. Using these

constants, the rate constants were calculated and compared

with the experimental kC values. There was a reasonable

agreement with each other (Table 1), which fortifies the

proposed mechanism (Scheme 1).

The increase in the rate, with increasing ionic strength,

is in favor of a reaction between charged species of reac-

tants, as presented in Scheme 1 of the proposed mecha-

nism. The effect of solvent on the reaction rate has been

described in detail in the literature [29]. In the present

study, the plot of log kC vs. 1/D is linear with negative

slope (Fig. 3) which seems to be contrary to the expected

reaction between neutral and anionic species in media of

lower relative permittivity. However, an increase in the rate

2+

CH 2CH

NH2

C

O

ORu

OH2

OH2

OH2

OH2

OH2

OH

Rate =�d½DPA�

dt¼ k1K1K2K3½AgðIIIÞ�½L�Pal�½OH

��½RuðIIIÞ�½H3IO2�

6 � þ K1½OH��½H3IO2�6 � þ K1K2½OH�� þ K3½H3IO2�

6 �½L-Pal]

þ K1K3½L-Pal][OH��½H3IO2�6 � þ K1K2K3½OH��½L-Pal]

ð7Þ

Rate

½DPA� ¼ kC ¼ kT � kU ¼k1K1K2K3½L�Pal�½OH



6 �½L-Pal]


ð8Þ


123

of the reaction with increasing relative permittivity may be

due to stabilization of the complex at high relative

permittivity.

The thermodynamic quantities for the different equi-

librium steps, in Scheme 1 can be evaluated as follows.

The [L-Pal] and [OH-] (Table 1) were varied at four dif-

ferent temperatures. The plots of [Ru(III)]/kC vs. 1/[L-Pal],

[Ru(III)]/kC vs. 1/[OH-] and [Ru(III)]/kC vs. [H3IO62]

should be linear as in Fig. 5a–c. From the slopes and

intercepts, the values of K1, K2 and K3 were calculated at

different temperatures. A van’t Hoff’s plot was made for

the variation of K1, K2 and K3 with temperature (log K1 vs.

1/T, log K2 vs. 1/T and log K3 vs. 1/T). The values of

enthalpy of reaction DH, entropy of reaction DS and free

energy of reaction DG were calculated for the first, second

and third equilibrium steps. These values are given in

Table 3. A comparison of the DH value (55.27 kJ mol-1)

from K1 with that of DH# (36.35 kJ mol-1) of rate limiting

step supports that the reaction before the rate determining

step is fairly fast as it involves low activation energy [30].

A negative value of DS# (-37.4 JK-1 mol-1) suggests that

intermediate complex is more ordered than the reactants

[31].

4.2 Mechanism of Osmium(VIII) Catalysis

Osmium(VIII) is known to form different complexes

at different OH- concentrations, [OsO4(OH)2]2- and

[OsO5(OH)]3-. At higher concentration of OH-, [OsO5

(OH)]3- is significant. At lower concentrations of OH-, as

employed in the present study and since the rate of oxi-

dation increased with increase in [OH-], it is reasonable

that [OsO4(OH)2]2- was operative and its formation is

important in the reaction. Added periodate retarded the

rate. First order dependency in [DPA] and catalyst

(Os(VIII)) and fractional order in [L-Pal] and [OH-] was

observed. To explain the observed orders the following

Scheme 2 has been proposed for osmium(VIII) catalysed

reaction

In the prior equilibrium step 1, the OH- deprotonates

the DPA to give a deprotonated diperiodatoargentate(III);

in the second step displacement of a ligand, periodate takes

place to give free periodate which is evidenced by decrease

in the rate with increase in [IO4-] (Table 5). It may be

expected that lower Ag(III) periodate species such as MPA

is more important active species in the reaction than DPA.

The inverse fractional order in [H3IO62-] might also be due

to this reason. In the pre rate determining stage, the

hydroxylated species of Os(VIII) combines with a mole-

cule of L-Pal to give an intermediate complex, which

further reacts with one mole of MPA in rate determining

step to give a Free radicle of derived from L-Pal with the

regeneration of the osmium(VIII) catalyst. This free radi-

cals from the L-Pal further reacts with another molecule of

MPA species in a fast step to give the products as given in

Scheme 2.

0

2

4

6

8

10

12

0 2 4 6 8 10 12

[Ru(

III)

]/kC

X 1

0-4

mol

dm

-3 s

1/[OH-] X 10-2 dm3 mol-1

295K

300K

305K

310K

0123456789

10

0 1 2 3 4

1/[L-Pal] X 103 dm3 mol-1

[Ru(

III)

]/kC

X 1

0-4 m

ol d

m-3

s

[Ru(

III)

]/kC

X 1

0-4 m

ol d

m-3

s

295K

300K305K310K

0

2

4

6

8

0 2 4 6

[H3IO62- ] X 10 -5 mol dm-3

(b)

(a) (c)Fig. 5 Verification of rate law

(8) of Ru(III) catalysed

oxidation of L-phenylalanine by

diperiodatoargentate(III).

a Plots of [Ru(III)]/kC vs.

1/[L-Pal] at four different

temperatures (conditions as in

Table 1). b Plots of [Ru(III)]/kC

vs. 1/[OH-] at four different


Table 1). c Plots of [Ru(III)]/kC

vs. [H3IO62-] at 27 �C

(conditions as in Table 1)


123

The probable structure of the complex (C2) is given

below;

Spectroscopic evidence for the complex formation

between Os(VIII) and L-pal was obtained from UV–vis

spectra of L-Pal (5.0 9 10-4), Os(VIII) (8.0 9 10-7,

[OH-] = 0.05 mol dm-3) and a mixture of both. A hyp-

sochromic shift of about 6 nm from 240 to 234 nm in the

spectra of Os(VIII) to mixture of Os(VIII) and L-Pal was

observed. The Michaelis–Menten plot proved the complex

formation between catalyst and substrate, which explains

less than unit order in [L-Pal]. Such a complex between a

catalyst and substrate has also been observed in other

studies [32].

From Scheme 2, the rate law (11) can be derived.

Equation 11 can be rearranged to Eq. 12, which is suitable

for verification.

½OsðVIIIÞ�kC

¼ ½H3IO2�6 �

k2K1K2K4½L-Pal][OH��

þ ½H3IO2�6 �

k2K2K4½L-Pal]þ 1

k2K4½L-Pal]

þ ½H3IO2�6 �

k2K1K2½OH�� þ½H3IO2�

6 �k2K2

þ 1

k2

ð12Þ

According to Eq. 12, other conditions being constant,

plots of [Os(VIII)]/kC vs. 1/[L-Pal], 1/[OH-] and [H3IO62-]

should be linear and are found to be so as in Fig. 6a–c.

The slopes and intercepts of such plots lead to the

values of K1, K2, K4 and k2 (Table 2) calculated as

(0.66 ± 0.04) dm3 mol-1 (2.3 ± 0.1) 9 10-4 mol dm-3,

(7.5 ± 0.2) 9 102 dm3 mol-1 and (2.4 ± 0.1) 9 105 dm3

mol-1 s-1, respectively. The value of K1 and K2 is in good

agreement with the literature [12]. Using these constants,

the rate constants were calculated and compared with the

experimental kC values. There was a reasonable agreement

with each other (Table 2), which fortifies the proposed

mechanism (Scheme 2).

The thermodynamic quantities for the different equi-

librium steps, in Scheme 2 can be evaluated as follows.

The [L-Pal] and [OH-] (Table 5) were varied at four

different temperatures. The plots of [Os(VIII)]/kC vs. 1/

[L-Pal], [Os(VIII)]/kC vs. 1/[OH-] and [Os(VIII)]/kC vs.

[H3IO62] should be linear. From the slopes and intercepts,

the values of K1, K2 and K4 were calculated at different

temperatures. A van’t Hoff’s plot was made for the varia-

tion of K1, K2 and K4 with temperature (log K1 vs. 1/T, log

K2 vs. 1/T and log K4 vs. 1/T). The values of enthalpy of

reaction DH, entropy of reaction DS and free energy of

reaction DG were calculated for the first, second and third

equilibrium steps. These values are given in Table 2. A

comparison of the DH value (78.4 kJ mol-1) from K1 with

that of DH# (10.5 kJ mol-1) of rate limiting step supports

that the reaction before the rate determining step is fairly

fast as it involves low activation energy [30].

The increase in the rate, with increasing ionic strength, is

in favor of a reaction between charged species of reactants, as

presented in Scheme 2 of the proposed mechanism. The

effect of solvent on the reaction rate is described in detail in

the literature [29]. For the limiting case of zero angle

approach between two dipoles or anion–dipole system, Amis

[29] has shown that a plot of log KC vs. 1/D gives a straight

line (Fig. 4), with a negative slopes for a reaction between

negative ion and a dipole or two dipoles and with a positive

slopes for a positive ion and dipole interaction. In the present

study, the plot observed had a negative slope, which is in the

right direction as shown in Scheme 2. The complex involved

in both the catalyst is expected to lead to negative entropy of

Os

O

O

O

O

O

O

H

H

CH2 CH

NH2

C

O

O

3-

Rate ¼ �d½DPA�dt

¼ k2K1K2K4½AgðIIIÞ�½L�Pal�½OH��½OsðVIIIÞ�

½H3IO2�6 � þ K1½OH��½H3IO2�

6 � þ K1K2½OH�� þ K4½H3IO2�6 �½L-Pal]


ð10Þ

Rate

½DPA]¼ kC ¼ kT � kU ¼

k2K1K2K4½L�Pal�½OH��½OsðVIIIÞ�

½H3IO2�6 � þ K1½OH��½H3IO2�

6 � þ K1K2½OH�� þ K4½H3IO2�6 �½L-Pal]


ð11Þ


123

activation and this is found to be the case. The negative value

of DS# (-107 JK-1 mol-1) suggests that intermediate com-

plex is more ordered than the reactants [31]. The observed

higher rate constant for the slow step indicate that the oxi-

dation presumably occurs via an inner-sphere mechanism.

This conclusion is supported by earlier observation [33].

The values of DS#, DG# and the rate constant (k) indicate

that the order of reactivity of the catalysts is Ru(III) \Os(VIII) for the oxidation of L-phenylalanine by DPA. The

Os(VIII)-catalysed reaction, however, is reasonably fast in

view of readiness of Os(VIII) to act across the double bond

and the Ru(III)-catalysed reaction is slower, probably owing

to the less ability of the Ru(III) to act across the double bond.

The activation parameters evaluated for the catalysed and

uncatalysed reactions explain the catalytic effect on the

reaction. The catalyst Ru(III) or Os(VIII) forms a complex

(C) with the substrate, which enhance the reducing property

of the substrate over that without that catalyst (Ru(III) or

Os(VIII)). Further, the catalyst Ru(III) or Os(VIII) modifies

the reaction path by lowering the energy of activation.

5 Conclusion

The comparative study of ruthenium(III) and osmium(VIII)

catalysed oxidation of L-Pal by diperiodatoargantate(III)

was studied. Oxidation products were identified. Among

the various species of Ag(III) in alkaline medium,

[Ag(H2IO6)(H2O)2] is considered to be the active species

for the title reaction. Active species of Ru(III) is found

to be [Ru(H2O)5(OH)2]2? and that for Os(VIII) is [OsO4

(OH)2]2-. Activation parameters were evaluated for both

uncatalysed and catalysed reactions with respect to slow

step of reactions Schemes. Catalytic constants and activa-

tion parameters with respect to catalyst were also com-

puted. The catalytic efficiency is Ru(III) \ Os(VIII).

Appendix

According to Scheme 1


¼ k1½C1�½Ag(H2IO6ÞðH2O)2�

¼ k1K1K2K3½DPA�½OH��½L�Pal�½RuðIIIÞ�

½H3IO2�6 �

ðA:1Þ

The total concentration of DPA is given by (where T and f

stands for total and free)

½DPA�T ¼ ½DPA�f + [Ag(H2IO6ÞðH3IO6Þ�2�

+ [Ag(H2IO6ÞðH2O)2�

¼ ½DPA�f þ K1½OH��½DPA� þ K2½AgðH2IO6ÞðH3IO6Þ�2�

½H3IO2�6 �

¼ ½DPA�f þ K1½OH��½DPA� þ K1K2½OH��½H3IO2�

6 �

¼ ½DPA�f 1þ K1½OH�� þ K1K2½OH��½H3IO2�

6 �

� �

¼ ½DPA�f½H3IO2�

6 � þ K1½OH��½H3IO2�6 � þ K1K2½OH��

½H3IO2�6 �

� �

0

2

4

6

8

10

12

14

16

18

0 2 4 6 8 10 12

295K

300K

305K

310K

[Os(

VII

I)]/

kC X

10-5

mol

dm

-3 s

1/[OH-] X 10-2 dm3 mol-1

0

1

2

3

4

5

6

7

8

0 1 2 3 4

1/[L-Pal] X 103 dm3 mo-1

[Os(

VII

I)]/

kC X

10-5

mol

dm-3

s

295K

300K305K

310K

0

4

8

12

16

0 1 2 3 4 5 6

[Os(

VII

I)]/

kC X

10-5

mol

dm-3

s

[H3IO 62-

] X 10-5

mol dm-3

(a)

(b)

(c)Fig. 6 Verification of rate law

(8) of Os(VIII) catalysed

oxidation of L-phenylalanine by

diperiodatoargentate(III).

a Plots of [Os(VIII)]/kC vs.

1/[L-Pal] at four different


Table 2). b Plots of [Os(VIII)]/

kC vs. 1/[OH-] at four different


Table 2). c Plots of [Os(VIII)]/

kC vs. [H3IO62-] at 27 �C

(conditions as in Table 2)


123

Therefore

½DPA�f ¼½DPA�½H3IO2�

6 �½H3IO2�

6 � þ K1½OH��½H3IO2�6 � þ K1K2½OH��

ðA:2Þ

Similarly,

½L-Pal]T ¼½L-Pal]f + [C1�¼½L-Pal]f þ K3½L-Pal][Ru(III)]

¼½L-Pal]ff1þ K3½Ru(III)]g

½L-Pal]f ¼½L�Pal�T

1þ K3½Ru(III)]

In view of the low concentration of [Ru(III)] used

½L-Pal]T ¼ ½L-Pal]f ðA:3Þ

Similarly

½Ru(III)]T ¼½Ru(III)]f + [C1�¼½Ru(III)]f þ K3½L-Pal][Ru(III)]

¼½Ru(III)]ff1þ K3½L-Pal]g

½Ru(III)]f ¼½RuðIIIÞ�T

1þ K3½L-Pal]

ðA:4Þ

Similarly

½OH��T ¼ ½OH��f + [Ag(H3IO6ÞðH2IO6Þ�2�

+ [Ag(H3IO6ÞðH2O2Þ�

¼ ½OH�� þ K1½DPA�½OH�� þ K1K2½DPA�½OH��½H3IO2�

6 �

In view of low concentration of [DPA] and [H3IO62-]

½OH��T ¼ ½OH��f ðA:5Þ

Substituting the Eqs. A.2, A.3, A.4 and A.5 in Eq. A.1 and

omitting the T and f subscripts, we get

Similarly, rate law was derived for osmium(VIII) catalysed

reaction.

References

1. Laloo D, Mohanti MM (1990) J Chem Soc Dalton Trans p 311

2. Balreddy K, Sethuram B, Navaneeth Rao T (1981) Indian J Chem

20A:395

3. Mahadevappa DS, Rangappa KS, Gowda NNM, Timmegouda B

(1982) Int J Chem Kinet 14:1183

4. Sethuram B (2003) Some aspects of electron—transfer reactions

involving organic molecules. Allied Publishers (P) Ltd, New

Delhi, p 78

5. Jaiswal PK (1972) Analyst 1:503

6. Venkata Krishna K, Jayaprakash Rao P (1998) Indian J Chem

37A:1106 References therein

7. Kumar A, Kumar P, Ramamurthy P (1999) Polyhedron 18:773

8. Kumar A, Vaishali, Ramamurthy P (2000) Int J Chem Kinet

32:286

9. Balikungeri A, Pelletier M, Monnier D (1977) Inorg Chim Acta

22:7

10. Krishenbaum LJ, Ambrus JH, Atkinson G (1973) Inorg Chem

12:2832

11. Das AK (2001) Coord Chem Revs 213:307

12. Lamani SD, Veeresh TM, Nandibewoor ST (2009) Russ J Phys

Chem (in press)

13. Saxena OC (1967) Microchem J 12:609

14. Reddy CS, Vijaykumar T (1995) Indian J Chem A34:615

15. Kamble DL, Chougale RB, Nandibewoor ST (1996) Indian J

Chem A35:865

16. Panigrahi GP, Misro PK (1978) Indian J Chem 16A:201

17. Cohen GL, Atkinson G (1964) Inorg Chem 3:1741

18. Jeffery GH, Bassett J, Mendham J, Denney RC (1996) Vogel’s

textbook of quantitative chemical analysis, 5th edn. ELBS,

Longman, Essex, pp 467–491


¼ k1K1K2K3½AgðIIIÞ�½L�Pal�½OH��½RuðIIIÞ�

½H3IO2�6 � þ K1½OH��½H3IO2�

6 � þ K1K2½OH�� þ K3½H3IO2�6 �½L-Pal]


ðA:6Þ

Rate

½DPA� ¼ kC ¼ kT � kU ¼k1K1K2K3½L�Pal�½OH



6 �½L-Pal]


ðA:7Þ


123

19. Fiegl F (1975) Spot tests in organic analysis. Elsevier, New york,

p 333

20. Moelwyn-Hughes EA (1947) Kinetics of reaction in solutions.

Oxford University Press, London, p 297

21. Aveston J (1969) J Chem Soc A p 273

22. Crouthamel CE, Hayes AM, Martin DS (1951) J Am Chem Soc

73:82

23. Cotton FA, Wilkinson G (1996) Advanced inorganic chemistry.

Wiley Eastern, New York, p 153

24. Chang R (1981) Physical chemistry with application to biological

systems. McMillan, New York, p 326

25. Kiran TS, Hiremath CV, Nandibewoor ST (2006) Appl Cata A

305:79

26. Shetter RS, Nandibewoor ST (2005) J Mol Catal A 238:137

27. Munavalli DS, Chimatadar SA, Nandibewoor ST (2008) Transi-

tion Met Chem 33:535–542

28. Seregar V, Veeresh TM, Nandibewoor ST (2007) Polyhedron

26:1731–1739

29. Moelwyn-Hughes EA (1961) Physical chemistry, 2nd edn.

Pergamon Press, New york

30. Rangappa KS, Raghavendra MP, Mahadevappa DS, Channego-

uda D (1998) J Org Chem 63:531

31. Weissberger A (1974) In: Lewis ES (ed) Investigation of rates

and mechanism of reactions in techniques of chemistry, vol 4.

Wiley, New York, p 421

32. Hiremath CV, Kiran TS, Nandibewoor ST (2005) J Mol Cat A p 163

33. Martinez M, Pitarque MA, Eldik RV (1996) J Chem Soc Dalton

Trans p 2665


123

Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidation of L-phenylalanine by Ag(III) Periodate...

Documents

Transcript of Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidation of L-phenylalanine by Ag(III) Periodate...