Ion-exchange resin catalysis in benign synthesis of perfumery grade p-cresylphenyl acetate from p-cresol and phenylacetic acid

Article abstract of DOI:10.1021/op0500133

p-Cresylphenyl acetate is a very important perfume that finds wide applications and possesses an organoleptic character similar to those of honey, nuts, and butter. It is produced by mineral acid-catalyzed esterification of p-cresol with phenylacetic acid. Use of homogeneous acid catalysts leads to posttreatment pollution problems apart from the quality-related issues. The current work is focused with an eco-friendly and benign catalytic process, employing the solid acid catalysts such as dodecatungstophosphoric acid (DTP) supported on K-10 clay, ion-exchange resins, sulfated zirconia, etc. for esterification of p-cresol with phenylacetic acid to p-cresylphenyl acetate. The order of catalytic activity was found to be Amberlyst-15 ≈ Indion-125 > 20% w/w DTP/K-10 > sulfated zirconia. Indion-125 was used for further experiments. It was observed that the catalyst has excellent reusability and that the reaction was 100% selective towards p-cresylphenyl acetate. A pseudo-first-order kinetic model was built up to fit the experimental data, and the apparent activation energy was found to be 9.56 kcal/mol.

Full text of DOI:10.1021/op0500133

Organic Process Research & Development 2005, 9, 288−293
Ion-Exchange Resin Catalysis in Benign Synthesis of Perfumery Grade
p-Cresylphenyl Acetate from p-Cresol and Phenylacetic Acid
Ganapati D. Yadav* and Sharad V. Lande
Department of Chemical Engineering, UniVersity Institute of Chemical Technology, UniVersity of Mumbai,
Matunga, Mumbai - 400 019, India
Abstract:
acids, etc.6
-17
The current work is concerned with the use
p-Cresylphenyl acetate is a very important perfume that finds
wide applications and possesses an organoleptic character
similar to those of honey, nuts, and butter. It is produced by
mineral acid-catalyzed esterification of p-cresol with pheny-
lacetic acid. Use of homogeneous acid catalysts leads to
posttreatment pollution problems apart from the quality-related
issues. The current work is focused with an eco-friendly and
benign catalytic process, employing the solid acid catalysts such
as dodecatungstophosphoric acid (DTP) supported on K-10 clay,
ion-exchange resins, sulfated zirconia, etc. for esterification of
p-cresol with phenylacetic acid to p-cresylphenyl acetate. The
order of catalytic activity was found to be Amberlyst-15 ≈
Indion-125 > 20% w/w DTP/K-10 > sulfated zirconia. Indion-
of cation-exchange resins to develop an environmentally
benign process for p-cresylphenyl acetate. The importance
of ion-exchange resins as catalysts has been reported in
several commercially relevant reactions in comparison with
1
8-33
other catalysts in our laboratory.
p-Cresylphenyl acetate imparts a warm, animal-like
background when used in jasmine, narcissus, and jonquille
2
,3
compositions. It is very useful as a fixative and is easier
to use than many other p-cresol derivatives. It also finds wide
application in fine fragrance, beauty care, soap, laundry care,
household products and possesses an organoleptic character
similar to those of honey, nuts, and butter. Among solid
catalysts, ion-exchange resins have been used for relatively
low-temperature reactions and are available in a variety of
forms and strengths. Apart from their prominence in separa-
tion and purification of products, ion-exchange resins4
have been used as catalysts in the manufacture of some
important chemicals such as MTBE, TAME, bisphenol A,
phenol alkylation, and dimethyl maleate; also the deactivation
of ion-exchange resins has been studied and modeled for
125 was used for further experiments. It was observed that the
catalyst has excellent reusability and that the reaction was 100%
selective towards p-cresylphenyl acetate. A pseudo-first-order
kinetic model was built up to fit the experimental data, and
the apparent activation energy was found to be 9.56 kcal/mol.
,11-13
1
. Introduction
Esterification is one of the most fundamental and impor-
1
2-31
industrial alkylation and acylation reactions.
In our laboratory, we have examined the efficacy of ion-
exchange resins with the reference to other solid acid
catalysts such as clays and their modified forms, supported
tant reactions used by industry because of the overwhelming
applications of esters as intermediates in the synthesis of fine
chemicals, drugs, plasticizers, perfumes, food preservatives,
1-4
cosmetics, pharmaceuticals, solvents, and chiral auxiliaries.
Production capacity for esters varies anywhere from a few
(
(
(
6) Yadav, G. D.; Mujeebur Rahuman, M. S. M. Clean Technol. EnViron. Policy
003, 5, 128.
7) Yadav, G. D.; Mujeebur Rahuman, M. S. M. Clean Technol. EnViron. Policy
004, 6, 114.
8) Yadav, G. D. Catal. SurVeys Asia 2004.
2
1-5
kilograms to several thousand kilograms per day. Several
synthetic routes have been adopted to make esters,1 but most
of them do not meet the stringent specifications that are being
applied in today’s chemically conscious world. The most
traditional method of making an ester is the mineral acid-
catalyzed reaction of the concerned carboxylic acid with an
alcohol, with one of them taken in molar excess to shift the
equilibrium conversion favourably by using a homogeneous
catalysts such as sulfuric acid, p-toluene sulphonic acid, HF,
HCl, phosphoric acid, etc. The advantages of using solid
heterogeneous catalysts are too well-known and among these
are zeolites, clays, ion-exchange resins, supported heteropoly
2
,4
(9) Yadav, G. D.; Nair, J. J. Microporous Mesoporous Mater. 1999, 33, 1.
10) Chitnis, S. R.; Sharma, M. M. React. Funct. Polym. 1997, 33, 93.
11) Chakrabarti, A.; Sharma, M. M. React. Funct. Polym. 1993, 20, 1.
(
(
(12) Sharma, M. M. React. Funct. Polym. 1995, 26, 3.
(
(
(
13) Harmer, M. A.; Sun, Q. Appl. Catal., A 2001, 221, 45.
14) Yadav, G. D.; Krishnan, M. S. Org. Process Res. DeV. 1998, 2, 86.
15) Yadav, G. D.; Kulkarni, H. B. React. Funct. Polym. 2000, 44, 153.
(16) Yadav, G. D.; Goel, P. K. Green Chem. 2000, 72.
(
(
17) Yadav, G. D.; Murkute, A. D. Int. J. Chem. React. Eng. 2004, 346, 389.
18) Yadav, G. D.; Joshi, A. V. Org. Process Res. DeV. 2001, 5, 408.
(19) Yadav, G.; Thathagar, M. B. React. Funct. Polym. 2002, 52, 111.
(20) Dixit, A. B.; Yadav, G. D. React. Funct. Polym. 1996, 31, 237.
(21) Dixit, A. B.; Yadav, G. D. React. Funct. Polym. 1996, 31, 251.
(22) Yadav, G. D.; Nalawade, S. P. Chem. Eng. Sci. 2003, 58, 2573.
(23) Yadav, G. D.; Krishnan, M. S.; Pujari, A. A.; Doshi, N. S.; Mujeebur
Rahuman, M. S. M. U.S. Patent 6,204,424, B1135, 2001.
*
To whom correspondence should be addressed. E-mail: gdyadav@yahoo.com,
gdy@udct.org.
(24) Yadav, G. D.; Pujari, A. A.; Joshi, A. V. Green Chem. 1999, 1, 269.
(25) Yadav, G. D.; Goel, P. K. Clean Technol. EnViron. Policy 2002, 4, 165.
(26) Yadav, G. D.; Nair, J. J. Langmuir 2000, 16, 4072.
(27) Yadav, G. D.; Nair, J. J. J. Chem. Soc., Chem. Commun. 1998, 21, 2369.
(28) Yadav, G. D.; Murkute, A. D. AdV. Synth. Catal. 2004, 346, 389.
(29) Yadav, G. D.; Murkute, A. D. J. Catal. 2004, 224, 218.
(30) Yadav, G. D.; Murkute, A. D. J. Phys. Chem. A 2004, 108, 9557.
(31) Yadav, G. D.; Kirthivasan, N. Appl. Catal., A 1997, 154, 29.
(32) Yadav, G. D.; Kirthivasan, N. J. Chem. Soc., Chem. Commun. 1995, 203.
(33) Yadav, G. D.; Thorat, T. S. Ind. Eng. Chem. Res. 1996, 35, 721.
(
(
(
1) Ogliaruso, M. A.; Wolfe, J. F. Synthesis of Carboxylic Acids, Esters and
Their DeriVatiVes; Wiley: New York, 1991.
2) Arctander, S. Perfume and FlaVor Chemicals; Steffen Arctander Publica-
tions: Elizabeth, NJ; 1988.
3) Bedoukian, P. Z. Perfumery and FlaVouring Synthesis, 3rd ed.; Allured
Publishing: Wheatson, IL, 1986.
(
(
4) Yadav, G. D.; Mehta, P. H. Ind. Eng. Chem. Res. 1994, 33, 2198.
5) Yadav, G. D.; Mujeebur Rahuman, M. S. M. Org. Process Res. DeV. 2002,
6
, 706.
2
88
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Vol. 9, No. 3, 2005 / Organic Process Research & Development
10.1021/op0500133 CCC: $30.25 © 2005 American Chemical Society
Published on Web 04/02/2005

heteropoly acids (HPA), zeolites, sulfated zirconia, a series
of UDCaT catalysts for developing clean and green industrial
processes in consonance with basic principles of green
chemistry. In continuation of our concerted efforts in
developing ecofriendly, active, and selective catalysts,
especially for esterification reactions where water is formed
as coproduct and has a significant impact on equilibrium and
overall conversion, the current work was undertaken. Fur-
thermore, there is practically no literature available on the
kinetics of esterification of p-cresol with phenylacetic acid
by using ion-exchange resin as catalysts. Hence, it would
be of special interest to study the esterification of p-cresol
with phenylacetic acid over cheap and easily available
catalysts such as ion-exchange resins.
2
. Experimental Section
2.1. Chemicals and Catalysts. Cation-exchange resins
Figure 1. Effect of various catalysts. p-Cresol; 0.2 mol;
phenylacetic acid: 0.006 mol; speed of agitation: 1000 rpm;
temperature: 90 °C.
Indion-125 and Amberlyst-15 were obtained from M/s Ion
Exchange (India) Ltd, Mumbai, India, and Rohm and Haas,
U.S.A., respectively. K-10 clay was obtained from Fluka,
Germany. Zirconium oxychloride, dodecatungstophosphoric
acid, phenylacetic acid, p-cresol were obtained from M/s s.d.
Fine Chemicals Pvt Ltd., Mumbai. All other chemicals were
analytical grade reagents and were used without further
purification. The catalysts used for the reaction were dried
at 110 °C for 4 h before use. Dodecatungstophosphoric acid
solid product was crystallized and filtered. The reaction mass
containing the unreacted p-cresol, phenylacetic acid, and
traces of product was recycled. There was no foreign
impurity introduced in the system. The product was purified
by recrystallization in methanol. Thus, product separation
and recovery and recycle of unreacted p-cresol was facilitated
under such reaction conditions. Moreover, the homogeneous
process, with drawbacks such as safe handling and disposal
of corrosive mineral acids, has been replaced with a better
heterogeneous catalytic process.
(
DTP)/K-10 ( 20% (w/w)) was prepared by a well-established
31,32
procedure in our laboratory.
prepared by an established procedure in our laboratory.
.2. Experimental Procedure, Analysis, and Isolation
Sulfated zirconia was also
3
3,34
2
2
.3. Reaction Scheme.
of Product. All experimental studies were conducted in a
glass reactor of 5 cm i.d. and 10 cm height with four glass
baffles and four bladed disc turbine impellers located at a
height of 0.5 cm from the bottom of the vessel and
mechanically agitated with an electric motor. A typical
experiment utilized 0.2 mol of p-cresol and 0.006 mol of
3
phenylacetic acid with a catalyst loading of 0.025 g/cm on
dry basis of total reaction volume at a agitation speed of
1
000 rpm at 90 °C under solventless conditions. The reaction
3
. Results and Discussion
.1. Effect of Various Catalysts. Different solid acid
mixture was allowed to reach the desired temperature, the
initial/zero time samples were withdrawn, and catalyst was
added thereafter. The analysis was done on a gas chromato-
graph (Chemito 8610) equipped with a flame ionisation
detector. A stainless steel column (2.5 m in length) packed
with 10% OV-17 supported on chromosorb-WHP was used
for the analysis. The injector and detector were kept at 300
3
catalysts were used to assess their efficacy in this reaction.
A 0.05 g/cm loading of catalyst based on the organic volume
3
of the reaction mixture was employed at a mole ratio of 30:1
p-cresol to phenylacetic acid at 90 °C and an agitational
speed of 1000 rpm. The catalysts used were Amberlyst-15,
Indion-125, 20% w/w DTP/K10, and sulfated zirconia. It was
found that cation-exchange resins Amberlyst-15 and Indion-
°
C. The oven temperature was programmed from 130 °C
-
1
(0.5 min) up to 280 °C with a ramp rate of 20 °C min .
125 showed higher conversions compared to other catalysts.
Synthetic mixtures were used to calibrate and quantify the
Figure 1 shows the conversion of phenylacetic acid, the
limiting reactant, for the various catalysts. The esterification
with ion-exchange resins Amberlyst-15 and Indion-125 was
quantitative and almost equivalent since basically these have
nearly similar exchange capacity. The ion-exchange capaci-
ties of Amberlyst-15 and Indion-125 are 4.90 and 4.86
mequiv/g-dry basis, respectively. There is only a slight
difference (3%) which can be taken as experimental error.
data. The product was confirmed by GC-MS.
An increase in mole ratio enhances the conversion by
orders of magnitude and is 95% at a mole ratio of 1:30 of
phenylacetic acid:p-cresol. The equilibrium is shifted greatly
to the right. The reaction is done under solventless conditions.
The reaction was conducted at 90 °C at which it was a clear
liquid solution. The catalyst was removed by hot filtration,
and then the mass was cooled to 50 °C or so, whereby the
DTP/K10 (20% w/w) and S-ZrO
2
offered low conversion.
(34) Kumbhar, P. S.; Yadav, G. D. Chem. Eng. Sci. 1989, 44, 2535.
It also suggests that Brønsted acids work better in esterifi-
Vol. 9, No. 3, 2005 / Organic Process Research & Development
•
289

cation reactions. Further experiments were conducted with
Indion-125 as the catalyst where only one parameter was
varied at a time under otherwise similar experimental
conditions. The selection of Indion-125 was also based on
its availability in local market at much cheaper rates than
the imported Amberlyst-15.
3.2. Effect of Speed of Agitation. This is typical solid-
liquid slurry reaction involving transfer of p-cresol (A) and
phenylacetic acid (B) from bulk liquid phase to catalyst
surface wherein external mass transfer of reactants to surface
of the catalyst particle, followed by intraparticle diffusion,
adsorption, surface reactions, and desorption take place. To
develop a true kinetic model the influence of the external
solid-liquid mass transfer resistance must be ascertained.
The overall reaction can be presented as follows:
solid acid catalyst
A + ZB
8 E + W
(1)
where A ) phenylacetic acid, B ) p-cresol E ) p-
cresylphenyl acetate, W ) water and z ) stoichiometric
coefficient reaction which is 1 for the present cases.
At steady state, the rate of mass transfer per unit volume
Figure 2. Effect of speed of agitation. p-Cresol: 0.2 mol;
phenylacetic acid: 0.006 mol; Indion-125: 0.05 g/cm . Particle
size: 500-710 µm; temperature: 90 °C.
3
In all reactions, p-cresol was taken in far molar excess
-
3
-1
of the liquid phase (mol cm s ) is given by:
(30:1) over phenylacetic acid to drive the equilibrium toward
the ester. To establish the influence of external resistance to
mass transfer of the reactants to the catalyst surface, the speed
of agitation was varied over the range of 800-1200 rpm,
for an average particle size of 500 µm. The conversion of
phenylacetic acid, the limiting agent, at different intervals
of time is shown in Figure 2. It was observed that the speed
of agitation had no effect of conversion beyond 1000 rpm;
thus, there was no limitation of external mass transfer of
p-cresol from bulk liquid phase to the outer surface of the
catalyst beyond this speed. Further experiments were con-
ducted at 1000 rpm.
RA ) kSL-AaP{[A ] - [A ]}
(2)
o
s
(
rate of transfer of A from bulk liquid to external surface
of the catalyst particle)
kSL-AaP{[B ] - [B ]} (3)
)
o
s
(
rate of transfer of B from bulk liquid to external surface
of the catalyst particle)
(4)
)
robs
(
observed rate of reaction within the catalyst particle)
According to eq 5, it is necessary to calculate the rates
of external mass transfer of both p-cresol (B) and phenyl-
acetic acid (A) and compare them with the rate of reaction.
For typical spherical particle, the particle surface area per
unit volume is given by
Here the subscripts “o” and “s” denote the concentration in
bulk liquid phase and external surface of the catalyst,
respectively.
Depending on the relative magnitudes of external resis-
tance to mass transfer and reaction rates, different controlling
mechanisms have been put forward.34 When the external
6w
aP )
(6)
(
F d )
mass transfer resistance is small, then the following inequality
holds:
P P
3
where w is the catalyst loading (g/cm ) of liquid phase, F
the density of particle (g/cm ), and d
P
3
1
1
1
P
is the particle diameter
.
and
(5)
robs KSL-AaP[A ]
KSL-AaP[Ao]
(cm). For this reaction, for the maximum catalyst loading
o
-
3
P
used (0.1 g cm ) with a particle size (d ) of 0.05 cm, in the
2
3
The observed rate could be given by three types of model
wherein the contribution of intraparticle diffusion resistance
could be accounted for by incorporation of the effectiveness
factor η. These models are:
current studies, a ) 20 cm /cm liquid phase.
P
For the maximum catalysts loading used in the current
2
3
studies, a )20 cm /cm . The solid-liquid mass transfer
P
coefficient, k , for the two reactants was calculated by using
SL
3
5
(1) the power law model if there is very weak adsorption
the correlations of Sano et al. which have been developed
for ion-exchange resin-type catalysts and take into account
the effects of Reynolds number and Schmidt number
of reactant species
(
(
2) the Langmuir-Hinshelwood-Hougen-Watson model
3) the Eley-Rideal model. It is there therefore necessary
4
P
3
1/4
1/3
to study the effect of speed of agitation, catalyst loading,
and particle size to ascertain the absence of external mass
and intraparticle diffusion resistance so that the true intrinsic
kinetic equation anc be used.
k d
ed F
µL
SL
P
L
)
2 + 0.4
(7)
(
) (
)
Dψ
µL
F D
L
where D is bulk diffusivity of the species (A or B), (in
290
•
Vol. 9, No. 3, 2005 / Organic Process Research & Development

2
-1
cm s ), ψ is shape factor, µ
L
) viscosity of liquid phase,
-3
F
L
1
) liquid density (g cm ), e ) power consumption in (ergs
s ).
-
Where
P
e )
)
F V
L
L
2
3
energy supplied per unit mass of slurry by agitation, cm /s
8)
(
where, the power is given by
3
5
I
P ) NpN D F
(9)
L
To evaluate N
P
it is necessary to calculate the Reynolds
number, which is given by
2
I
D NF
L
NRe
)
(10)
µL
Figure 3. Effect of catalyst loading. p-Cresol: 0.2 mol;
phenylacetic acid: 0.006 mol; particle size: 500-710 µm; speed
of agitation: 1000 rpm; temperature: 90 °C.
N
P
) power number, N ) speed of agitation, rps, D
I
)
L
impeller diameter, cm, V ) volume of the liquid phase, F
L
-
3
)
liquid density (g cm ).
The diffusivity values (D) can be calculated by using the
Wilke-Change equation, and these values are as follows:
catalyst is proportional to a
catalyst where the concentrations of A and B are [A
[B ], respectively. For a spherical particle, a is also
P
, the exterior surface area of the
36
s
] and
-
5
2
-1
-5
2
s
P
D
AB ) 4.77 × 10 cm s and DBA) 4.86 × 10 cm
-
1
proportional to w, the catalyst loading per unit liquid volume
as shown in eq 6. It is possible to calculate the values of
[A ] and [B ]; for instance,
s s
s . Thus, the corresponding values of the solid-liquid mass
transfer coefficients for both of the reactants were obtained
-
3
as follows: kSL-A for phenylacetic acid is 2.79 × 10 cm/s
-3
for kSL-B for p-cresol 2.84 × 10 cm/s. Thus, it was possible
kSL-Aa {[A ] - [A ]} ) r
obs
P
o
s
to calculate various resistances. A typical initial rate of
-
8
3
reaction was calculated as 6.04 × 10 mol/cm ‚s, and
therefore using appropriate values in eq 5, the following is
obtained.
at steady state.
{[A ] - [A ]} ) 1.07 × 10 mol/cm
-
6
3
∴
o
s
7
4
4
3
1
.6 x 10 . 1.9 x 10 and 5.9 x 10 cm ‚s/mol
-4
Thus, using the appropriate values, [A
s
] ) 2.709 × 10
-
3
-4
mol cm which is nearly equal to [A
o
] (2.72 × 10 mol
The above inequality implies that there is an absence of
resistance due to the solid-liquid external mass transfer for
both the species A and B and the rate may be either surface-
reaction controlled or intraparticle-diffusion controlled.
Therefore, the effect of catalyst loading and particle size was
studied to ascertain the influence of intraparticle resistance.
-
3
cm ), similarly [B ] ) [B]. Thus, any further addition of
s
catalyst did not have any bearing on external mass transfer.
The experimental observation is thus consistent since the
reaction could be limited by intraparticle diffusion or by
reaction on the pore walls within the catalyst particle
(
intrinsic reaction), for which the effect of particle size
needed to be considered.
.4. Proof of Absence of Intraparticle Resistance. The
3.3. Effect of Catalyst Loading. In the absence of mass
transfer resistance, the rate of reaction is directly proportional
to catalyst loading based on the entire volume of the liquid
phase. The catalyst loading was varied over a range of 0.01-
3
effect of particle size of the catalyst on the reaction rate was
studied by taking three different particle size ranges to assess
the influence of intraparticle resistance. From Figure 4 it is
observed that, as the particle size decreases, the conversion
increases. However, the conversion for 710-500 and 300-
-
3
0
.1 g cm on the basis of the total volume of the reaction
mixture. Figure 3 shows the effect of catalyst loading on
the conversion of phenylacetic acid. It indicates that as the
catalyst loading is increased, the conversion of phenylacetic
acid increases which is due to proportional increase in the
number of active sites. At higher catalyst loading the rate of
mass transfer is excessively high and therefore there is no
more increase in the rate.
2
00 µm differed only by a mere 2%. Thus, particles in the
size range of 710-500 µm were used for further experiments.
The average particle diameter of the catalyst used in the
reactions was 0.06 cm, and thus, a theoretical calculation
was done on the basis of the Wiesz-Prater criterion to assess
As shown by eqs 1 and 2, at steady state, the rate of
external mass transfer to the exterior surface area of the
37
the influence of intraparticle diffusion resistance. According
to the Wiesz-Prater criterion, the dimensionless parameter,
(
(
35) Sano, Y.; Yamaguchi, N.; Adachi, T. J. Chem. Eng. Jpn. 1974, 7, 225.
36) Reid, R. C.; Prausnitz, J. M.; Sherwood, T. K. The Properties of Gases
and Liquids, 3rd ed.; McGraw-Hill: New York, 1977.
(37) Fogler, S. H. Elements of Chemical Reaction Engineering, 2nd ed.; Prentice-
Hall: New Delhi, 1995.
Vol. 9, No. 3, 2005 / Organic Process Research & Development
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291

Figure 4. Effect of particle size. p-Cresol: 0.2 mol; phenyl-
acetic acid: 0.006 mol; Indion-125: 0.05 g/cm ; speed of
agitation: 1000 rpm; temperature: 90 °C.
Figure 5. Effect of mole ratio. Phenylacetic acid: p-cresol,
Indion-125 0.05 g/cm . Particle size: 500-710 µm; speed of
agitation: 1000 rpm; temperature 90 °C.
3
3
C
wp, which represents the ratio of the intrinsic reaction rate
to intraparticle diffusion rate can be evaluated from the
observed rate of reaction, the particle radius (R ) and effective
diffusivity of the limiting reactant (D ), and the concentration
P
e
of the reactant at the external surface of the particle.
2
(
i) If Cwp ) robs P P
F R /D [A ] . 1
e
s
then the reaction is limited by severe internal diffusion
resistance.
(ii) If Cwp , 1
then the reaction is intrinsically kinetically controlled.
The effective diffusivity of phenylacetic acid (De-A) inside
the pores of the catalyst was obtained from the bulk
-6
diffusivity (DAB), porosity (ꢀ), and tortusity (τ) as 9.7 × 10
cm s where De-A ) DAB(ꢀ/τ). In the present case, the value
2
-1
-
2
of Cwp was calculated as 4.3 × 10 for the initial observed
rate which is much less than 1, and therefore, the reaction is
intrinsically kinetically controlled. A further proof of the
absence of the intraparticle diffusion resistance was obtained
by studying the effect of temperature.
Figure 6. Effect of temperature. p-Cresol: 0.2 mol; phenyl-
acetic acid: 0.006 mol; Indion-125: 0.05 g/cm . Particle size:
3
5
00-710 µm; speed of agitation: 1000 rpm; temperature: 90
°
C.
3
.5. Effect of Mole Ratio. The mole ratio of phenylacetic
factor and energy of activation. The values of the frequency
factor k and the energy of activation were calculated as 6
acid to p-cresol was changed from 1:1 to 1:30 mol under
otherwise similar sets of conditions. With an increase in mole
ratio, the conversion of phenylacetic acid had increased
Figure 5).
3
on conversion under otherwise similar conditions was studied
in the range of 70-100 °C as shown in Figure 6. The
conversion of phenylacetic acid was found to increase
substantially with increasing temperature up to 100 °C.
To elucidate the kinetic parameter a pseudo-first-order
model was attempted with the experimental data (Figure 7),
and it was found to fit the data well. The values of rate
constants at different temperatures were calculated and an
Arrhenius plot (Figure 8) was used to estimate the frequency
0
3
3
-1 -1
× 10 cm mol
s
and 9.56 kcal/mol, respectively. This
activation energy also supported the fact that the overall rate
of reaction is not influenced by either external mass transfer
or intraparticle diffusion resistance and it is an intrinsically
kinetically controlled reaction on active sites.
(
.6. Effect of Temperature. The effect of temperature
3.7. Reusability of Catalyst. Reusability of Indion-125
was tested by conducting two runs (Figure 9). It is observed
that for every reuse the rate of reaction and conversion
decreases. After the reaction, the catalyst was filtered and
then refluxed with 50 mL of toluene for 30 min to remove
any adsorbed material from the catalyst surface and pores
and dried at 110 °C after every use. It was observed that
there is only a marginal decrease in conversion, in the final
292
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Vol. 9, No. 3, 2005 / Organic Process Research & Development

Figure 7. Pseudo-first-order kinetic plot of esterification of
p-cresol with phenylacetic acid.
Figure 9. Reusability of catalyst. p-cresol: 0.2 mol; phenyl-
acetic acid: 0.006 mol; Indion-125: 0.05 g/cm . Particle size:
3
5
00-710 µm; speed of agitation: 1000 rpm; temperature: 90
°
C.
the reaction is intrinsically kinetically controlled. The product
separation workup is simple.
Acknowledgment
G.D.Y. acknowledges Darbari Seth Endowment for sup-
porting the Chair and NMITLI CSIR.
NOMENCLATURE
A ) phenylacetic acid
[A
i
] ) concentration of phenylacetic acid at i, mol/cm3
B ) p-cresol
] ) concentration of B at i, mol/cm3
[B
i
E ) p-cresylphenyl acetate
H ) water
Figure 8. Arrhenius plot.
Z ) stoichiometric coefficient
) solid-liquid interfacial area, cm /cm3
2
a
P
conversion from 95 to 87% in second reuse. Some catalyst
was lost during filtration. There was no makeup catalyst
added during the second use. Thus, the catalyst was reusable
up to three times. The product is perfumery grade with no
contamination of any mineral acid or sulfur.
D
AB ) mutual diffusion coefficient of solute A at very low concentra-
tion in solvent B, cm /s
2
k
SL-A,
k
SL-B ) solid-liquid mass-transfer coefficients for A and B
2
D
e
) effective diffusivity cm /s
) diameter of the particle, cm
d
P
4
. Conclusions
Greek Symbols
) density of catalyst particle, g/cm3
η ) effectiveness factor
The current work has focused on the synthesis of
F
P
perfumery-grade p-cresyl-phenyl acetate by esterification of
p-cresol with phenylacetic acid using different solid acid
catalysts such as Amberlyst-15, Indion-125, 20% w/w DTP/
K-10, and sulfated zirconia. The order of catalytic activity
was found to be Amberlyst-15 > Indion-125 > DTP/K-10
τ ) tortuosity, dimensionless
Subscripts
o ) bulk phase
s ) catalyst surface
>
sulfated zirconia. Indion-125 was used for further experi-
ments. It was observed that the catalyst has excellent
reusability, and the reaction was 100% selective towards
p-cresyl phenylacetate A pseudo-first-order kinetic model
was built up to fit the experimental data, and the apparent
activation energy is 9.56 kcal/mol, which also suggested that
Received for review February 7, 2005.
OP0500133
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