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Journal of Molecular Catalysis A: Chemical 306 (2009) 11–16

Contents lists available at ScienceDirect

Journal of Molecular Catalysis A: Chemical

journa l homepage: www.e lsev ier .com/ locate /molcata

olvent effects on the reaction rate and selectivity of synchronouseterogeneous hydrogenation of cyclohexene and acetone

n ionic liquid/alcohols mixtures

ohammad Khodadadi-Moghaddama, Aziz Habibi-Yangjehb, Mohamad Reza Gholamia,∗

Department of Chemistry, Sharif University of Technology, P.O. Box 11365-9516, Tehran, IranDepartment of Chemistry, Faculty of Science, University of Mohaghegh Ardabili, P.O. Box 179, Ardabil, Iran

r t i c l e i n f o

rticle history:eceived 2 November 2008eceived in revised form 7 February 2009ccepted 9 February 2009

a b s t r a c t

Synchronous heterogeneous catalytic hydrogenation of cyclohexene and acetone, catalyzed by Pt/Al2O3,was carried out in solutions of 2-hydroxy ethylammonium formate (a room temperature ionic liquid,RTIL) with ethanol and propan-1-ol at 25 ◦C. Rate constants and selectivity of the reaction (relative tocyclohexene hydrogenation) increase with mole fraction of the ionic liquid (IL). The reactants tendency

vailable online 21 February 2009

eywords:onic liquideterogeneous catalytic hydrogenationolvatochromic parameters

to the catalyst surface increases by addition of the ionic liquid and thus the reaction rate increases,especially for cyclohexene hydrogenation. Consequently the selectivity to cyclohexene hydrogenationwas increased. Single-parameter correlations of log k vs. �* (dipolarity/polarizibility) gives reasonableresults in the solution. The increase of the reaction rate with �* is attributed to the non-polar nature ofthe reactants.

olvent effectselectivity

. Introduction

Selective hydrogenation is an important process both in homo-eneous and heterogeneous catalysis. Its primary target is theydrogenation of a specific unsaturated bond (e.g., C C, C C or

O), while leaving other unsaturated bonds within the moleculeor in other molecules) unaffected [1]. The selective hydrogenationf a C C bond or a C O bond in a molecule with both a C C bondnd a C O bond is important for the preparation of fine chemicalsnd is of academic interest [2]. The catalytic selective hydrogena-ion of ˛,ˇ-unsaturated aldehydes to the saturated aldehydes is onexample. Platinum catalyst is known to be one of the most effectiveatalysts for this selective hydrogenation. However, such selectiveeactions become quite problematic when the carbon–carbon dou-le bond of an a,b-unsaturated aldehyde is conjugated both to aarbonyl group and an aromatic ring.

Catalytic hydrogenation is one of the most useful, versatile, andnvironmentally acceptable reaction routes available for organicynthesis, and the reaction is usually carried out in a liquid-phase

sing batch type slurry processes and a supported noble metal (Pd,t, or Rh) catalyst [3–6]. Major advantages of multi-phase catalyticeactions using solid catalysts include easy separation of catalystsnd products, easy recovery and catalyst recycling, and relatively

∗ Corresponding author. Tel.: +98 21 66165314; fax: +98 21 66005718.E-mail address: gholami@sharif.edu (M.R. Gholami).

381-1169/$ – see front matter. Crown Copyright © 2009 Published by Elsevier B.V. All rigoi:10.1016/j.molcata.2009.02.018

Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.

mild operating conditions [7,8]. The performance of noble metalcatalysts in liquid-phase hydrogenation is found to be dependenton several factors such as liquid composition (substrate structure,solvent effect, etc.), catalyst nature (active sites composition andmorphology, support effect, modifiers, etc.), and reaction condi-tions (temperature, pressure, etc.) [9].

In the production of fine chemicals over heterogeneous catalysts,the choice of the solvent has a crucial impact; a bad selection of thesolvent leads to a complete loss of selectivity and/or activity, thusdestroying the possible utilization of a potentially efficient processin practice. Therefore, the choice of a solvent and the understand-ing of solvent effects are of central importance and thus require acareful investigation.

Solvent effects are widely studied and the phenomena knownas solvent effects cover a very broad topic [10,11]. The effects ris-ing from the use of different solvents are observed as variations inactivity, selectivity and stereoselectivity. However, several factorscan be responsible for these variations, e.g., solubilities of liquidand gaseous reactants and their adsorption on the catalyst surface,competitive adsorption of solvent molecules, interaction of solventwith the reactant(s) either in the liquid-phase or on the catalystsurface as well as catalyst deactivation caused by the solvent [12].

Therefore, the phenomena understood under the label of solventeffects are a combination of very different physical and chemicalphenomena and thus it is difficult to understand them completely.

Ionic liquids (ILs) are attracting much interest in various areas ofchemical synthesis, electrochemistry, separations and biotransfor-

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ations, owing to their unique physicochemical characters [13,14].mong these areas, catalysis in ILs is an exciting and burgeoningrea of intense research and has been extensively reviewed recently15–19]. It is reported that the use of ILs as reaction media for theatalytic transformations can have a profound effect on activity andelectivity. However, in the large majority of cases studied to date,Ls have been focused on the application in homogeneous catalysisr catalytic reactions in which catalysts were performed in situ, onlyminority relates to catalysis using heterogeneous catalysts. Cat-

lytic hydrogenation reactions have exactly the same circumstancess other catalysis, as far as we know, only a few works done abouthe heterogeneous hydrogenation of ˛,ˇ-unsaturated aldehydes inLs using supported metal catalysts and most of them found betterelectivity for the reduction of conjugated C C bond by using ILs asolvents compared with conventional molecular organic solvents20–27].

Currently, most of the data available about RTILs focus on bulkhysical properties, such as phase transitions, viscosity and density,nd on the correlation between these properties and the molecu-ar structure of the RTILs. Little is known about the microscopichysical properties of these new materials and how to predict the

nfluence of these solvents on chemical reaction rates. Such under-tanding would give the necessary information to synthesize newTILs with precisely tailored properties for every chemical reaction.TILs can replace molecular solvents only if they can be comparedo the generally used reaction media. Therefore, it is necessary tonderstand how the RTILs are able to affect organic reactivity. Inddition, one of the largest barriers to the application of RTILs arisesrom their high viscosity which may produce a reduction in theate of many organic reactions. Several attempts have been madeo improve the properties of RTILs, including the search for newnd unusual RTILs in addition to ‘green’ cosolvents such as water,thanol, and supercritical CO2. Unfortunately, no data has beeneported on the ability of these mixtures in affecting organic reac-ivity [28]. Hence, the study of the effects of ionic liquid alteringhysicochemical properties on solute species and their reactionssing molecular solvents is becoming an increasingly active area ofesearch [29,30].

In continuing our investigations into solvent effects on rate ofrganic reactions [31–36], we focused on the effect of the IL on thectivity and selectivity for C C and C O hydrogenation in alcoholicolvents at 25 ◦C (use of acetone hydrogenation to propan-2-ol andyclohexene hydrogenation to cyclohexane as model reactions).latinum catalysts supported on Al2O3 prepared by the impreg-ation method are used for this reaction. The catalysts have beenharacterized by nitrogen adsorption at 77 K and XRD methods.

. Experimental

Ethanol was obtained from Merck, propan-1-ol from Fluka andthanolamine and formic acid from Riedel de Haen. The chemicalsere of the highest purity available and purified according to the

iterature [37].

.1. Ionic liquid synthesis

The RTIL was prepared as described in literature [38]. 2-minoethanol (59.9 g, 0.1 mol) was placed in a three-necked flaskquipped with a reflux condenser, a dropping funnel and a ther-ometer. The flask was mounted in an ice bath. Under vigorous

tirring with a magnetic stirrer, 38 ml (0.1 mol) formic acid was

dded dropwise to the flask in about 45 min. Stirring was contin-ed for 24 h at room temperature to obtain a colorless viscous clear

iquid. The RTIL was identified via H-NMR and FT-IR spectroscopys described elsewhere [38] and it was degassed for 2 h in vacuum0.3 mbar at 80 ◦C) before use.

ular Catalysis A: Chemical 306 (2009) 11–16

2-Hydroxy ethyl ammonium formate, as a new ionic liquid, ismiscible with water and small alcohols and phase separation can-not be observed even for weeks [38]. Mixed solvents were preparedby carefully mixing the components by weight. Karl Fischer titra-tions showed no detectable presence of water in freshly synthesizedRTIL. Solvatochromic parameters were obtained from our previouswork [31]. Concentration measurements were taken on a HP6890gas chromatograph (GC) with 60 m HP5 column.

2.2. Catalyst preparation

Pt/Al2O3 catalyst was prepared impregnating alumina withexcess liquid. The impregnation solution was prepared by dissolv-ing 500 mg PtCl2 (Merck) in 30 ml deionized water and 10 ml HCl(Merck). 5 g of �-alumina was added to the impregnation solutionand stirred for 30 min. The impregnated solid was separated bydecantation of the solution and dried at 100 ◦C for 12 h. The cat-alyst was reduced in hydrogen flow (120 ml/min) at 400 ◦C for 1 hand was characterized with XRD and BET methods.

2.3. Catalyst characterization

Specific area and porosity were obtained from nitrogenadsorption–desorption isotherms at 77 K performed in an auto-matic Quantachrom apparatus (Model Quantasorb) with Belsorpadsorption/desorption data analysis software in the 0.05–0.995 rel-ative pressure ranges. BET surface area was calculated from a linearpart of the BET plot according to IUPAC recommendations. Poresize distributions were calculated from the N2 adsorption branchusing the Horvath–Kawazoe model. Mean pore diameter and totalpore volume (P/P0 = 0.99) were calculated from BET plot by Belsorpadsorption/desorption data analysis software.

XRD pattern of the catalyst was carried out from 4◦ to 70◦ (2�)using a Brruker D4 X-ray diffractometer operating at 40 kV and30 mA with Cu K� radiation (�=1.542 Å) and a Ni filter. Counts wereaccumulated every 0.02 (2�) at a scan speed of 1◦ (2�/min) in 25 ◦C.

2.4. Catalytic test

In a typical run, a solution of reagents in solvent (0.2 g cyclo-hexene and 0.3 g acetone in 20 ml solvent) was added to 50 mlthree-necked flask attached to a thermometer, a condenser anda hydrotreator (including a hydrogen cylinder, hydrogen flowme-ter and valves). After replacing the air in the flask completely withhydrogen, 0.02 g of alumina supported platinum was added. Thereaction mixture was stirred vigorously with a magnetic stirrer(1250 rpm) and was kept at desired temperature (25 ◦C). During thereaction, 1 �l of reaction mixture (at least 6 times in a kinetic run)was taken and injected to the GC (60 m HP-5 column, film thickness1 �m, inside diameter 0.25 mm and FID detector). The surface areaof the reactant peak in GC chromatogram was used for detectionof concentrations in reaction mixture (with calibration curve). TheRTIL was decomposed in the injector of GC (temperature 220 ◦C)and gives several peaks in 12–15 min in the GC chromatogram, butdid not influence the reactant peak that appeared in 5.4 min in ourtemperature program for GC oven.

The absorption of hydrogen in ionic liquid was carried out undermagnetic stirring (1250 rpm) at a pressure of 1 atm and at roomtemperature (25 ◦C) by passing a gas stream (20 ml/min) via a finelysintered glass frit through 20 g of degassed (0.3 mbar, 2 h at 80 ◦C)

ionic liquid loaded into 100 ml three-necked flask. The temperaturewas controlled with NESLAB RTE-8 thermometer. After 30 min, 1 �lof the mixture was injected to the GC (HP-5 column, TCD detector)and the amount of dissolved hydrogen was determined by compar-ing the H2 peak area with the calibration curve.

Molecular Catalysis A: Chemical 306 (2009) 11–16 13

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M. Khodadadi-Moghaddam et al. / Journal of

The adsorption of acetone and cyclohexene on catalyst sur-ace in solvent mixtures was carried out under magnetic stirring1250 rpm) at a pressure of 1 atm and at room temperature (25 ◦C)y injecting the solution before and after adding the catalyst (0.02 g)o 20 g solvent including 0.2 g cyclohexene and 0.3 g acetone in00 ml round button flask.

. Results and discussion

.1. Catalyst characterization

The catalyst reduced at 400 ◦C exhibits the fcc (Face Cubic Cen-ered) XRD pattern with peaks at 2� = 41.02, 46.48, and 67.88.he average crystallite size, L of the catalyst particle, was deter-ined by XRD line broadening technique using Scherrer’s equation,

= 0.94�/bcos �; in which � is the wavelength of X-ray and b is theelative peak broadening. The crystallite size of Pt particles wasbtained to be 5.8 nm. In addition, the mean diameter of poresbtained from BET plot and pore size distribution was 8.05 and.45 nm, respectively. The BET surface area and the total pore vol-me (P/P0 = 0.990) of the supported Pt catalyst was 373.7 m2 g−1

nd 0.7519 cm3/g, respectively.

.2. Hydrogen solubility

Ionic liquids have been demonstrated to be excellent solventsor many reactions involving gaseous reactants entering RTIL solu-ion; such as hydrogenation, hydroformilation, and oxidation. Theolubility of gases in RTILs depends markedly on the type of RTILs39,40]. In contrast with other ionic liquids, H2 is well dissolved in-hydroxy ethylammonium formate. In Fig. 1, one can see that theddition of the RTIL to ethanol and propan-1-ol increases the hydro-en solubility in the media. Maximum H2 solubility was observedn the pure ionic liquid.

.3. Adsorption of reactants on catalyst

In order to demonstrate the relationship between adsorption ofeactants on the catalyst in the media, we investigated the adsorp-ion of cyclohexene and acetone on Pt/Al2O3 (Figs. 2 and 3). As

an be seen, adsorption of cyclohexene and acetone on the catalystncrease with addition of the RTIL to ethanol and propan-1-ol. Also,ehavior of the acetone adsorption is similar to the cyclohexene.

n both RTIL–alcohol mixtures, extent of cyclohexene adsorptions higher than the acetone. Molecules of cyclohexene do not have

ig. 1. H2 solubility in the RTIL–alcohol mixtures (�, ethanol–RTIL mixture; �,ropan-1-ol–RTIL mixture) at 25 ◦C.

Fig. 2. Adsorption of reactants on Pt/Al2O3 in ethanol/RTIL mixture (�, cyclohexeneadsorption; � acetone adsorption; C0, initial concentration; C, concentration at theend of the test) at 25 ◦C.

polar group, then there is no reasonable interaction of the media.For this reason, tendency of cyclohexene molecules to surface ofthe catalyst is higher than that of acetone. Due to this non-polarnature, its tendency to the surface was increased with increasingthe polarity of the media (Table 1).

In order to obtain the relationship between reactants adsorptionand the solvatochromic parameters of media, we used multi-parameter linear regression (MLR) method. The results show thatadsorption of the reactants on the catalyst has negative correlationwith the solvent basicity (ˇ) parameter and adsorption of ace-tone and cyclohexene was decreased with increasing the basicityof the media. Also, dipolarity/polarizibility (�*) of the media haspositive correlation with adsorption of the reactants. But the corre-lation with ˇ parameter is better than �*(in cyclohexene adsorptionfor all mixtures: r = 0.931 and in acetone adsorption for all mix-tures: r = 0.968). Negative effect of ˇ extent of the adsorption canbe explained by competitive adsorption of solvent molecules on thecatalyst surface. The basic solvent can be adsorbed better than theacidic solvent and can fill the active sites on the catalyst surface.

Cyclohexene is a very weak base molecule compared to acetone,thus the influence of the ˇ parameter is stronger for cyclohexeneadsorption in comparison to the acetone molecules.

3.4. Solvent effects on the reaction kinetics

The first-order rate constants of the reaction in mixtures ofthe RTIL with ethanol and propan-1-ol were obtained in variousmole fractions of the RTIL at 25 ◦C. The reaction rate constants

Fig. 3. Adsorption of reactants on Pt/Al2O3 in propan-1-ol/RTIL mixture (�, cyclo-hexene adsorption; � acetone adsorption; C0, initial concentration; C, concentrationat the end of the test) at 25 ◦C.

14 M. Khodadadi-Moghaddam et al. / Journal of Molecular Catalysis A: Chemical 306 (2009) 11–16

Tab

le1

Firs

t-or

der

rate

con

stan

tof

the

reac

tion

inm

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res

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TIL

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mic

par

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ers

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edia

.

XIL

RTI

L–et

han

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reR

TIL–

pro

pan

-1-o

lmix

ture

k cyc

l.(×

10−2

s−1g−1

)k a

cet.

(×10

−2s−1

g−1)

S(k

cycl

./kac

et.)

EN T

�*

ˇ˛

k cyc

l.(×

10−2

s−1g−1

)k a

cet.

(×10

−2s−1

g−1)

S(k

cycl

./kac

et.)

EN T

�*

ˇ˛

0.0

0.70

0.25

2.80

0.65

0.51

0.91

0.97

0.50

0.26

1.92

0.54

0.4

91.

070.

740.

10.

790.

263.

040.

840.

630.

911.

270.

610.

292.

100.

800.

561.

041.

230.

20.

860.

273.

190.

850.

68

0.93

1.27

0.69

0.32

2.16

0.81

0.6

1.02

1.24

0.3

0.98

0.29

3.38

0.85

0.72

0.91

1.22

0.79

0.36

2.19

0.82

0.66

0.98

1.21

0.4

1.10

0.32

3.4

40.

850.

790.

871.

180.

900.

402.

250.

820.

710.

951.

180.

51.

210.

353.

460.

860.

810.

891.

181.

00

0.43

2.36

0.83

0.76

0.91

1.16

0.6

1.35

0.39

3.46

0.85

0.89

0.81

1.12

1.20

0.4

92.

450.

840.

800.

891.

150.

71.

600.

453.

560.

870.

940.

791.

111.

380.

552.

510.

840.

870.

831.

110.

82.

130.

553.

870.

871.

010.

721.

071.

800.

64

2.81

0.86

0.95

0.76

1.09

0.9

3.17

0.70

4.53

0.89

1.04

0.71

1.08

2.60

0.74

3.51

0.88

0.98

0.74

1.10

1.0

4.34

0.86

5.05

0.89

1.15

0.59

1.01

4.34

0.86

5.05

0.89

1.15

0.59

1.01

Fig. 4. First-order rate constants for cyclohexene hydrogenation (�, ethanol–RTILmixture; �, propan-1-ol–RTIL mixture) at 25 ◦C.

were calculated by plotting the logarithm of concentration ofcyclohexene vs. time and are summarized in Table 1. The solva-tochromic parameters for mixtures of the RTIL with ethanol andpropan-1-ol at various compositions have been determined in ourlaboratory (Table 1). Figs. 4 and 5 demonstrate plot of the reactionrate constant vs. mole fraction of the RTIL. As can be seen, rateconstant of the reaction increases with mole fraction of the RTIL.

First-order rate constant of the hydrogenation reaction in theRTIL is approximately 8.7 and 3.3 times higher than propan-1-ol forcyclohexene and acetone, respectively. Although, the normalizedpolarity parameter (EN

T ) of the RTIL is higher than those of ethanoland propan-1-ol and it increases with mole fraction of the RTIL,but single-parameter correlations of log k vs. EN

T do not give accept-able results in the solutions (in cyclohexene hydrogenation forethanol–RTIL mixtures: r = 0.6025, for propan-1-ol–RTIL mixtures:r = 0.735 and for all mixtures: r = 0.684 and in acetone hydro-genation for ethanol–RTIL mixtures: r = 0.570, for propan-1-ol–RTILmixtures: r = 0.778 and for all mixtures: r = 0.627). Normalizedpolarity parameter is blend of �* (dipolarity/polarizability) and˛ (hydrogen-bond donor acidity) of the media [41,42]. Therefore,correlations of log k vs. �* and ˛ in the solutions were consid-ered. Hydrogen-bond donor acidity (˛) parameter of the media firstincreases with increasing the mole fraction of the molecular solventand then decreases. In fact in all cases the synergistic effect is obvi-

ous for ˛ parameter near the pure molecular solvents. This behavioris different from the continuously increase in log k vs. XIL. Single-parameter correlation of log k vs. ˛ does not give good results inthe solutions (in cyclohexene hydrogenation for ethanol–RTIL mix-tures: r = 0.506, for propan-1-ol–RTIL mixtures: r = 0.234 and for all

Fig. 5. First-order rate constants for acetone hydrogenation (�, ethanol–RTIL mix-ture; �, propan-1-ol–RTIL mixture) at 25 ◦C.

Molecular Catalysis A: Chemical 306 (2009) 11–16 15

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M. Khodadadi-Moghaddam et al. / Journal of

ixtures: r = 0.333 and in acetone hydrogenation for ethanol–RTILixtures: r = 0.547, for propan-1-ol–RTIL mixtures: r = 0.174 and for

ll mixtures: r = 0.375).The dipolarity/polarizibility parameter (�*) increases continu-

usly with the RTIL mole fraction in all mixtures. Single-parameterorrelations of log k vs. �* give acceptable results in the solutionss demonstrated in Eqs. (1)–(4):

for acetone hydrogenation in ethanol–RTIL mixture:

log k = −7.272(±0.171) + 2.074(±0.201)� ∗(n = 11, r = 0.960, S.E. = 0.1227, F1,10 = 106.74) (1)

for acetone hydrogenation in propan-1-ol–RTIL mixture:

log k = −7.051(±0.076) + 2.037(±0.091)� ∗(n = 11, r = 0.991, S.E. = 0.0564, F1,10 = 498.55) (2)

for cyclohexene hydrogenation in ethanol–RTIL mixture:

log k = −6.689(±0.235) + 2.900(±0.275)� ∗(n = 11, r = 0.962, S.E. = 0.1682, F1,10 = 110.98) (3)

for cyclohexene hydrogenation in propan-1-ol–RTIL mixture:

log k = −7.229(±0.117) + 3.413(±0.141)� ∗(n = 11, r = 0.992, S.E. = 0.0843, F1,10 = 587.37) (4)

here n, r, S.E., and F are number of data, regression coefficient,tandard error and statistical Fisher number, respectively. As cane seen, first-order rate constant of the reactions increases withipolarity/polarizability parameter of media in the mixtures of theTIL with the molecular solvents.

Linear correlation of log k vs. �* gives acceptable result in allolutions for hydrogenation of acetone:

log k = −7.136(±0.132) + 2.025(±0.157)� ∗(n = 21, r = 0.945, S.E. = 0.1343, F1,10 = 166.85) (5)

lso, similar result is obtained for hydrogenation of cyclohexene inll solutions:

log k = −6.974(±0.146) + 3.171(±0.174)� ∗(n = 21, r = 0.971, S.E. = 0.1489, F1,10 = 333.25) (6)

he values of log k do not show an acceptable dual-parameterorrelation with the solvatochromic parameters. Furthermore,hree-parameter correlations of log k vs. ˇ, ˛, and �* did notive reasonable results and the equations reduced to single-arameter correlations with dipolarity/polarizability of the media.hus, the best model is a single-parameter correlation ofog k vs. �*.

In the liquid-phase reactions, an increase in solvent polarityesults in an increase in the rates of certain reactions in which theharge density is greater in the activated complex than the reac-ants [42]. In heterogeneous catalytic hydrogenation, the reaction

ccurs on the surface of the catalyst (far from bulk of solvent). Thenhe solvent cannot directly affect the energetic level of reactantsnd activated complex of the reactions. Polar solvents increase thedsorption of non-polar substrates on the catalyst while non-polarolvents facilitate the adsorption of polar species [43]. However, inome cases, hydrogenation activity decreases with increasing sol-ent polarity due to competitive adsorption of high polar solventnd substrate on the catalyst surface [44,45].

Fig. 6. Selectivity of the hydrogenation reaction (S = kcycl./kacet.) in (�) ethanol–RTILand (�) propan-1-ol–RTIL mixtures at 25 ◦C.

3.5. Solvent effects on the reaction selectivity

We define the selectivity of the reaction as the ratio of the rateconstant for cyclohexene relative to the acetone:

S = kcycl.

kacet.(7)

There are many studies on the selectivity of C C and C O bonds[46–48]. Solvent effects on the selectivity of the reaction are stud-ied in details but many of them are in homogeneous phase [49–53].As can be seen in Fig. 6, selectivity of C C bond hydrogenationwas increased with increasing mole fraction of the RTIL. Maximumselectivity was observed in the RTIL. As we mentioned before, thedipolarity/polarizibility (�*) of the solvent is the main parameterin reaction rate constant. Also, dependence of hydrogenation rateconstant for cyclohexene to �* of the media is more than acetone(first-order rate constant of the reaction in the RTIL is approximately8.7 and 3.3 times higher than propan-1-ol for cyclohexene and ace-tone respectively), thus changes of kcycl. with �* of media is morethan kacet. values. For this reason, the selectivity of the reaction tocyclohexene hydrogenation increases with increasing the �* of themedia and addition of the RTIL.

4. Conclusion

Rate constants of synchronous heterogeneous catalytic hydro-genation of cyclohexene and acetone in mixtures of an RTIL withethanol and propan-1-ol were determined at 25 ◦C. In both mix-tures, the reaction rate constant and selectivity for cyclohexenehydrogenation increase with increasing mole fraction of the RTIL. Itwas demonstrated that dipolarity/polarizibility of the media has animportant role in determining solvent effects on the reaction rateconstant and the selectivity. This was attributed to the non-polarnature of the reactants. The reactants tendency to the catalyst sur-face increases by increasing the dipolarity/polarizibility of mediaand thus the reaction rate increases. In conclusion, the reaction rateconstant and the selectivity for heterogeneous catalytic hydrogena-tion in mixtures of a RTIL with molecular solvents are correlated tothe solvatochromic parameters of media.

Acknowledgment

The authors are grateful to Sharif University of Technology forfinancial support.

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