Friedel-Crafts propionylation of veratrole to 3,4-dimethoxypropiophenone over superacidic UDCaT-5 catalyst

Article abstract of DOI:10.1016/j.apcata.2011.10.027

3,4-Dimethoxypropiophenone (3,4-DMPP) is of considerable commercial importance due to its use in fine chemical and drug industries. 3,4-DMPP is traditionally produced by the Friedel-Crafts propionylation of veratrole using homogeneous catalysts which are

Full text of DOI:10.1016/j.apcata.2011.10.027

Applied Catalysis A: General 411–412 (2012) 123–130
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Applied Catalysis A: General
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Friedel–Crafts propionylation of veratrole to 3,4-dimethoxypropiophenone over
superacidic UDCaT-5 catalyst
Ganapati D. Yadav∗, Santosh R. More
Department of Chemical Engineering, Institute of Chemical Technology1, Nathalal Parekh Marg, Matunga, Mumbai 400 019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
3,4-Dimethoxypropiophenone (3,4-DMPP) is of considerable commercial importance due to its use in fine
chemical and drug industries. 3,4-DMPP is traditionally produced by the Friedel–Crafts propionylation
of veratrole using homogeneous catalysts which are highly polluting. Zeolites have also been used but
they are known to deactivate rapidly. A variety of novel solid acid catalysts such as UDCaT-4 (persulfated
alumina zirconia on hexagonal mesoporous silica, HMS), UDCaT-5 (superacidic modified sulfated zirco-
nia) and UDCaT-6 (modified sulfated zirconia nanoparticles on HMS) were synthesized in our laboratory
and characterized. Amongst them UDCaT-5 was the most active and selective. The current work deals
with development of clean and benign route for 3,4-DMPP synthesis using UDCaT-5 as catalyst in the
absence of any solvent. Effects of various parameters were studied in order to optimize the conversion
of veratrole and selectivity to 3,4-DMPP. Based on the experimental data a suitable mathematical model
was developed to represent the reaction kinetics.
Received 11 September 2011
Received in revised form 15 October 2011
Accepted 18 October 2011
Available online 25 October 2011
Keywords:
Solid superacids
Veratrole
Friedel–Crafts acylation
Kinetics
Selectivity
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
reported for the Friedel–Crafts of acylation of aromatics [7–9].
However, there is a limited literature on veratrole propionylation
Friedel–Crafts acylation and alkylation reactions are amongst
the most versatile methods of synthesizing substituted aromatic
compounds which serve as precursors for a variety of industrial
processes [1]. Aromatic ketones are valuable intermediates as well
as end products in an extensive range of value-added chemicals,
which include pharmaceuticals, agrochemicals, biocides, flavors,
fragrances and fine chemicals [2].
3,4-Dimethoxypropiophenone (3,4-DMPP) is of considerable
commercial importance due to its use in fine chemical and drug
industries. 3,4-DMPP is traditionally produced by the Friedel–Crafts
propionylation of veratrole (VT) by using homogeneous catalysts
such as AlCl3, TiCl4, FeCl3, SnCl4, CF3SO3H, FSO3H and H2SO4 [3,4].
These catalysts are highly polluting and corrosive. More than stoi-
chiometric quantities of the catalyst are used which are neutralized
at the end of reaction leading to effluent treatment problems.
Recently, the use of solid catalysts, such as Nafion-H [5], clays [6],
heteropoly acids [7], FeSO4, Fe2(SO4)3 and metal oxides promoted
by sulfate ions (SO42−/Al2O3), SO42−/ZrO2, SO42−/TiO2), have been
to 3,4-DMPP [10].
In particular, sulfated zirconia is the most powerful solid
superacid which is used in a number of reactions of industrial util-
ity [11–19]. All published literature shows that sulfated zirconia
has been prepared with a maximum 4% w/w of sulfur with preser-
vation of tetragonal phase which is responsible for its superacidic
nature. Above this sulfur content, the tetragonal phase of zirco-
nia is strongly affected and the superacidity reduced. It would be
most advantageous to synthesize sulfated zirconia with sulfur con-
tent above 4% while retaining the tetragonal phase to attain high
superacidity. A series of novel catalysts, named as UDCaTs, were
thus prepared. These catalysts have been tested in a number of reac-
tions in our laboratory [20–24]. Yadav and Murkute reported for the
first time the preparation of sulfated zirconia with the highest sul-
fur content (9%), by using chlorosulfonic acid as a new source for
sulfate ion [23]. This new catalyst was designated as UDCaT-5. The
acronym, UDCaT stands for the University Department of Chemical
Technology (UDCT) by which this institute was popularly known
until recently.
The current work delineates novelties of UDCaT series of cat-
alysts in Friedel–Crafts acylation of veratrole using propionic
anhydride under solventless conditions. UDCaT-5 was found to be
the most active, selective and robust catalyst. The overall process is
green and clean. This work also deals with development of a kinetic
model.
∗
Corresponding author. Tel.: +91 22 3361 1001x1111/2222;
fax: +91 22 3361 1002x1020.
E-mail addresses: gd.yadav@ictmumbai.edu.in, gdyadav@yahoo.com
(G.D. Yadav).
1
Formerly University of Mumbai Institute of Chemical Technology, now a sepa-
rate university.
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.10.027

124
G.D. Yadav, S.R. More / Applied Catalysis A: General 411–412 (2012) 123–130
2.1.1. Preparation of UDCaT-4
Nomenclature
A mixture of 2.39 g zirconium oxychloride and 0.11 g aluminum
nitrate was dissolved in deionised water and added to 5 g of precal-
cined hexagonal mesoporous silica (HMS) by the incipient wetness
technique. The solid material was dried in an oven at 110 ◦C for 3 h.
The dried material was hydrolyzed with ammonia gas and washed
with deionized water until a neutral filtrate was obtained. The
absence of chloride ion in the filtrate was detected by the silver
nitrate test. A material balance on chloride ions before and after
precipitation, and washing showed no retention on the solid. The
solid was then dried in an oven for 24 h at 110 ◦C. Persulfation was
carried out by immersing the above solid material in 0.5 M aque-
ous solution of ammonium persulfate for 30 min. It was dried at
110 ◦C for 24 h and calcined at 650 ◦C for 3 h to get the active catalyst
UDCaT-4 [20].
A
B
reactant species A, veratrole
reactant species B, propionic anhydride
concentration of A in bulk liquid phase (mol/cm3)
concentration of B in bulk liquid phase (mol/cm3)
chemisorbed A
A0
B0
AS
BS
C
chemisorbed B
3,4-dimethoxy propiophenone
propionic acid
D
aP
CA
CAS
surface area per unit liquid volume, cm2/cm3
concentration of A (mol/cm3)
concentration of
(mol/cm3)
A at solid (catalyst) surface
CB
concentration of B (mol/cm3)
CBS
concentration of
B at solid (catalyst) surface
2.1.2. Preparation of UDCaT-5
(mol/cm3)
UDCaT-5 was prepared by adding aqueous ammonia solution
to zirconium oxychloride solution at a pH of 9–10. The precipitated
zirconium hydroxide so obtained was washed with deionized water
until a neutral filtrate was obtained. The absence of chloride ion was
detected by AgNO3 test. Zirconium hydroxide was dried in an oven
for 24 h at 100 ◦C and was crushed to 100 mesh size. It was then
added to a solution containing 15 cm3/g of 0.5 M chlorosulfonic acid
in ethylene dichloride and mixed using a glass rod. The material was
left for 5 min in the solution under careful moisture-free condition
and kept in an oven as such. The temperature was raised slowly to
120 ◦C and maintained for 24 h. Thereafter it was calcined at 650 ◦C
for 3 h to get the active catalyst UDCaT-5 [23].
CC
CD
CS
Ct
M
dP
DAB
DBA
concentration of C in ( = mol/cm3)
concentration of D in ( = mol/cm3)
concentration of vacant sites (mol/cm3)
total concentration of the sites (mol/cm3)
mole ratio of B to A
diameter of catalyst particle (cm)
diffusion coefficient of A in B (cm2/s)
diffusion coefficient of B in A (cm2/s)
kSL-A, kSL-B solid–liquid mass transfer coefficients (cm/s)
De
CWP
RP
effective diffusivity (cm2/s)
Weisz Prater parameter
particle radius, cm
kB
chemisorption rate constant for forward reaction
chemisorption rate constant for backward reaction
2.1.3. Preparation of UDCaT-6
kꢀB
−rB
−rA
kSR
KB
UDCaT-6 was prepared by adding an aqueous solution of 2.5 g
zirconium oxychloride to 5 g precalcined HMS by incipient wetness
technique and it was dried in an oven at 120 ◦C for 3 h. The mate-
rial was hydrolyzed with ammonia gas and washed with distilled
water until no chloride ions were detected which was confirmed
by the AgNO3 test. It was further dried in an oven for 2 h at 120 ◦C.
Zr(OH)4/HMS was immersed in 15 cm3/g of 0.5 M chlorosulfonic
acid in ethylene dichloride. It was soaked for 5 min in the solution
and oven-dried to evaporate the solvent at 120 ◦C for 30 min. The
sample was then kept in an oven at 120 ◦C for further 24 h and cal-
cined thereafter at 650 ◦C for 3 h to get the active catalyst UDCaT-6
[24].
rate of chemisorption of B (mol cm−3 s−1
)
rate of surface reaction of A (mol cm−3 s−1
)
reaction rate constant (cm6 mol−1 g−1 s−1
)
adsorption equilibrium constant for B (cm3/mol)
robs
observed rate of reaction based on liquid phase vol-
ume (mol cm−3 s−1
vacant site
)
S
Sh
w
XA
Sherwood number
catalyst loading (g cm−3) of the liquid phase
fractional conversion of A
Greek letters
ꢀP
ꢁ
ꢂ
ε
ꢃ
density of catalyst particle (g/cm3)
viscosity of solvent, poise
effectiveness factor
porosity
2.2. Reaction procedure
The reaction was carried out in a 50 mL capacity glass reactor
of 3.5 cm i.d. equipped with four equally spaced baffles and a six-
bladed turbine impeller. The reaction temperature was maintained
within 0.5 ◦C of the set value by means of a thermostatic oil bath, in
which the reaction assembly was immersed. Standard experiments
were carried out by taking 0.04 mol veratrole, 0.2 mol propionic
anhydride and 3% v/v of n-dodecane (internal standard), and 1.26 g
catalyst loading (0.04 g/cm3 liquid-phase) at 80 ◦C. The total liq-
uid phase volume was 31.5 cm3. All catalysts were dried at 120 ◦C
for 3 h before use. The reaction mixture was allowed to reach the
desired temperature and the initial sample collected. Agitation was
then commenced at a desired speed. Catalyst-free samples were
withdrawn periodically up to 2 h.
tortuosity
2. Experimental
2.1. Chemicals and catalysts
The following chemicals were procured from reputed firms
and used without further purification: Veratrole, propionic anhy-
dride, zirconium oxychloride, aqueous ammonia solution (s.d. Fine
Chem. Ltd., Mumbai, India), hexadecyl amine, chlorosulfonic acid
(Spectrochem. Ltd., Mumbai, India), tetraethyl orthosilicate (Fluka,
Germany). Hexagonal mesoporous silica (HMS) was prepared by
a procedure described elsewhere [25]. The catalysts were dried
at 393 K for 3 h before use. UDCaT-4, UDCaT-5 and UDCaT-6 were
prepared according to the procedures developed by us [20,23,24].
2.3. Method of analysis
Analysis of the reaction mixture was performed by GC (Chemito,
model 8610) by using flame ionization detector and a stainless steel
column (3.25 mm diameter and 4 m length) packed with a station-
ary phase of 10% OV-17 supported on chromosorb-WHP. Typically

G.D. Yadav, S.R. More / Applied Catalysis A: General 411–412 (2012) 123–130
125
Fig. 1. Ammonia TPD: S–ZrO2 and UDCaT-5 catalysts.
Fig. 2. FT-IR of S–ZrO2 and UDCaT-5.
propionic anhydride was taken in excess and the conversions were
based on the limiting reactant veratrole. The quantification of data
was done through internal standard method. The products were
confirmed by GC-MS.
high sulfur content of 9% in UDCaT-5 and the quantity of tetragonal
phase of zirconia in UDCaT-5 is the same as that in the ordinary
S–ZrO2. The BET surface area of UDCaT-5 (83 m2 g−1) is lower than
that of S–ZrO2 (103 m2 g−1). The surface area of S–ZrO2 gradually
increases at low sulfate contents up to 4% w/w (119 m2 g−1) but it
decreases abruptly at a sulfate content of 5.64% (71 m2 g−1) due to
the migration of sulfate ions to the bulk phase of zirconia.
3. Results and discussion
3.1. Characterization of UDCaT-5
UDCaT-5 was completely characterized by FT-IR, XRD, BET sur-
face area, ammonia-TPD and elemental analysis and the details
were published by our laboratory [23]. Only a few salient features
are reported here. The ammonia-TPD was used to determine the
acid strength of UDCaT-5. It shows that apart from intermediate
and strong acidic sites present in sulfated zirconia, UDCaT-5 also
contains superacidic sites (Fig. 1). The elemental analysis showed
complete absence of chloride species and that 9% w/w S as sul-
fate was retained on the surface of UDCaT-5. In contrast, only 4%
of S in the form of sulfate ion was retained on S–ZrO2 wherein
the sulfation was done by using 1N sulfuric acid. The FT-IR spec-
tra of the S–ZrO2 show a similar pattern as UDCaT-5 indicating
the presence of bidentate chelating sulfate group (in C2ꢄ symmetry
with ꢄ3 at 1218, 1152, and 1066 and ꢄ1 at 997 cm−1) coordinated
to zirconia [26,27]. The absence of a band at 1400 cm−1 indicates
2−
that no polynuclear sulfates S2O7
were formed on the surface
of UDCaT-5. The band at 1631–1642 cm−1 is attributed to ıO–H
-
bending frequency of water molecules associated with the sulfate
group, suggesting that chlorosulfonic acid was decomposed dur-
ing calcination at 923 K and the sulfate ions were retained on the
surface of the UDCaT-5 (Fig. 2). Powder XRD was used to eluci-
date the crystalline phase of UDCaT-5 and S–ZrO2 (Fig. 3). It is
observed that crystal structure of zirconia is not affected by the
Fig. 3. XRD diffractogram S–ZrO2 and UDCaT-5 catalyst.

126
G.D. Yadav, S.R. More / Applied Catalysis A: General 411–412 (2012) 123–130
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
0
20
40
60
80 100 120 140 160 180 200
Time (min)
0
20
40
60
80
100 120 140 160 180 200
Time (min)
1000 rpm
UDCaT-6
UDCaT-4
UDCaT-5
800 rpm
1200 rpm
Fig. 4. Effect of various catalysts on conversion of veratrole. Veratrole: 0.04 mol, pro-
pionic anhydride: 0.2 mol, catalyst loading: 0.04 g/cm3, temperature: 80 ◦C, speed
of agitation: 1000 rpm.
Fig. 5. Effect of speed of agitation on conversion of veratrole. Veratrole: 0.04 mol,
propionic anhydride: 0.2 mol, catalyst: UDCaT-5, catalyst loading: 0.04 g/cm3, tem-
perature: 80 ◦C.
3.2. Efficacies of various catalysts
3.4. Proof of absence of external mass transfer resistance
Various solid acid catalysts based on sulfated zirconia were
used to assess their efficacy in this reaction, namely, UDCaT-4
(persulfated alumina zirconia on HMS), UDCaT-5 (superacidic mod-
ified sulfated zirconia) and UDCaT-6 (modified sulfated zirconia
nanoparticles on HMS). A 0.04 g/cm3 loading of the particular cat-
alyst based on the total organic volume of the liquid phase was
employed at 80 ◦C at a speed of agitation of 1000 rpm. It was
observed that UDCaT-4 and UDCaT-6 catalysts showed much lower
conversions than UDCaT-5, although all of them are highly selective
for 3,4-DMPP.
This is a typical solid–liquid slurry reaction involving the
transfer of veratrole, the limiting reactant (A) and propionic
anhydride (B) from the bulk liquid phase to the catalyst. It is fol-
lowed by intra-particle diffusion of the reactant, adsorption of
reactants, surface reaction and desorption of products. The influ-
ence of external solid–liquid mass transfer resistance must be
ascertained before a true kinetic model could be developed.The
reaction of veratrole (A) with propionic anhydride (B) produces
3,4-dimethoxypropiophenone (C) and propionic acid (D).
A + B → C + D
(1)
UDCaT-5 (most active) > UDCaT-4 > UDCaT-6 (least)
At steady state, the rate of mass transfer of A per unit volume of the
liquid phase (mol cm−3 s−1) is given by:
This is directly correlated with their acid strength. UDCaT-5
showed the highest activity (Fig. 4). Hence further experiments
were conducted with UDCaT-5 due to its excellent activity and
selectivity. Furthermore, propionylation of veratrole was also car-
ried out by using propionic acid as acylating agent over UDCaT-5 at
the same experimental conditions. No acylation product could be
obtained since the formation of the carbocation by dehydration of
propionic acid did not occur.
RA = kSL-Aap{[A0] − [AS]}
(2)
Similarly, the rate of transfer of B from bulk liquid phase to external
surface of the catalyst particle is give by:
RB = kSL-Bap{[B0] − [BS]}
(3)
(4)
robs = (observed rate of reaction within the catalyst particle)
Here the subscripts “0” and “S” denote the concentrations in bulk
liquid phase and external surface of catalyst, respectively. Depend-
ing on the relative magnitudes of the external resistance to mass
transfer and reaction rates, different controlling mechanisms have
been put forward [29]. When the external mass transfer resistance
is negligible, then the following inequality holds:
3.3. Effect of speed of agitation
The effect of speed of agitation was studied in the range of
800–1200 rpm at a catalyst loading 0.04 g/cm3 at 80 ◦C. The mole
ratio of veratrole to propionic anhydride was kept at 1:5 (Fig. 5).
There was no significant change in the rate and conversion patterns,
which was indicative of the absence of external mass transfer resis-
tance. However, all further reactions were carried out at a speed
of 1000 rpm. Theoretical calculations were also done to establish
that there was absence of external mass transfer resistance. We
have given the theoretical development in some of our earlier work
[25,28] and a typical calculation is presented here.
1
robs
1
>>
(5)
kSL-Aap[A0]
and also:
1
1
>>
robs
(6)
kSL-Bap[B0]

G.D. Yadav, S.R. More / Applied Catalysis A: General 411–412 (2012) 123–130
127
80
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
0
20
40
60
80 100 120 140 160 180 200
0
20 40 60 80 100 120 140 160 180 200
Time (min)
0.03 gm/cc 0.04 gm/cc
Time (min)
1:03
0.02 gm/cc
0.05 gm/cc
1:01
1:05
Fig. 6. Effect of catalyst loading on conversion of veratrole. Veratrole: 0.04 mol, pro-
pionic anhydride: 0.2 mol, catalyst: UDCaT-5, temperature: 80 ◦C, Speed of agitation:
1000 rpm.
Fig. 8. Effect of mole ratio on conversion of veratrole. Catalyst: UDCaT-5, catalyst
loading: 0.04 g/cm3, temperature: 80 ◦C, speed of agitation: 1000 rpm.
For a typical spherical particle, the particle surface area per unit
liquid volume is given by
The observed rate robs could be given by three types of mod-
els wherein the contribution of intra-particle diffusion resistance
could be accounted for by incorporating the effectiveness factor ꢂ.
These models are as follows:
6w
ap
=
(7)
ꢀpdp
where w is the catalyst loading (g/cm3) of liquid phase, ꢀp the den-
sity of particle (g/cm3) and dp is the particle diameter (cm). For
this system the maximum catalyst loading used was 0.04 g/cm3
for an average particle size (dp) of 0.0125 cm. Thus, ap was
calculated as 18.46 cm2/cm3. Therefore, the contribution of exter-
nal mass transfer coefficient could be calculated. The values of
liquid-phase diffusivity of the reactants A (veratrole) and B (pro-
pionic anhydride), denoted by DAB and DBA, were calculated by
using the Wilke–Chang equation at 80 ◦C as 1.43 × 10−5 cm2/s and
1.52 × 10−5 cm2/s, respectively [30]. The solid–liquid mass transfer
coefficients for both A and B were calculated from the limiting value
of the Sherwood number (e.g. Sh-A = kSL-Adp/DAB) of 2. The actual
Sherwood numbers are typically higher by order of magnitude in
well-agitated system but for conservative estimations a value of
2 was taken. The solid–liquid mass transfer coefficients kSL-A and
kSL-B values were obtained as 2.30 × 10−3 and 2.44 × 10−3 cm/s. The
initial rate of the reaction was calculated from conversion profiles.
A typical calculation shows that for a typical reaction, the initial
(a) The power law model if there is weak adsorption of reactant
species.
(b) Langmuir–Hinshelwood–Hougen–Watson model.
(c) Eley–Rideal mechanism.
6
5
4
3
rate of the reaction was calculated as 4.12 × 10−7 mol cm−3 s−1
.
Therefore, by using the appropriate values in (5) and (6) above:
2
R
= 0.9802
2
1
0
1
robs
1
1
>>
and
kSL-Aap[A0]
kSL-Bap[B0]
i.e. 2.43 × 106 ꢁ 1.85 × 104 and 3.49 × 103
The above inequalities also demonstrate that there is absence
of resistance to transfer of both A and B from the liquid phase
to the external surface of the catalyst particles, and the rate may
be controlled either surface reaction or intra-particle diffusion.
Therefore, the effect of catalyst loading at a fixed particle size and
temperature were studied to evaluate the influence of intra-particle
resistance. All further reactions were carried out at agitation speed
of 1000 rpm.
0
0.02
0.04
0.06
Catalyst loading (g/cm3)
Fig. 7. Plot of initial rate of reaction as a function of catalyst loading in liquid phase.

128
G.D. Yadav, S.R. More / Applied Catalysis A: General 411–412 (2012) 123–130
(i) If CWP = robsꢀpR2/De[AS] >> 1, then the reaction is limited by
70
60
50
40
30
20
10
0
severe intra-parPticle diffusion resistance.
(ii) If CWP ꢂ 1, then the reaction is intrinsically kinetically con-
trolled.
The effective diffusivity of veratrole (De-A) inside the pores of
the catalyst was obtained from the bulk diffusivity (DAB), porosity
(ε) and tortuosity (ꢃ) as 1.91 × 10−6 cm2/s, where De-A = DAB (ε/ꢃ).
In the present case, the value of CWP was calculated as 0.0011 from
the initial observed rate. Since CWP is much less than 1, the reaction
is intrinsically kinetically controlled. Further proof of the absence
of the intra-particle diffusion resistance was obtained through the
study of the effect of temperature which will be discussed later.
3.7. Effect of mole ratio
The effect of mole ration of veratrole to propionic anhydride
was studied at 1:1, 1:3 and 1:5 by keeping the catalyst loading per
unit volume constant. The conversion of veratrole was found to
increase with an increase in concentration of propionic anhydride
(PA) (Fig. 8). It leads to a higher concentration of electrophile PA to
react with veretrole, resulting in higher reaction rate and conver-
sion of veratrole. Therefore, all reactions were studied by using a
veratrole to propionic anhydride mole ratio of 1:5.
0
20
40
60
80
100
120
140
160
180
200
Time (min)
60° C 70° C
50° C
80° C
Fig. 9. Effect of temperature on conversion of veratrole. Veratrole: 0.04 mol, pro-
pionic anhydride: 0.2 mol, catalyst: UDCaT-5, catalyst loading: 0.04 g/cm3, speed of
agitation: 1000 rpm.
3.8. Effect of temperature
3.5. Effect of catalyst loading
The effect of temperature on conversion was studied under oth-
erwise similar conditions at 50, 60, 70 and 80 ◦C. It was observed
that the conversion increased with temperature (Fig. 9). This would
suggest a kinetically controlled mechanism. The initial rates of reac-
tion were calculated at different temperatures and the Arrhenius
plot was made to determine the energy of activation (Fig. 10). It
was found to be 7.32 kcal/mol, which is an indication of the overall
rate being controlled by intrinsic kinetics.
In the absence of external mass-transfer resistance, the rate of
reaction is directly proportional to the catalyst loading based on the
entire liquid-phase volume. The catalyst loading was varied over
range of 0.02–0.05 g/cm3 on the basis of total volume of the liquid
phase. Fig. 6 shows the effect of catalyst loading on the conversion
of veratrole. The initial rates of reaction are plotted against catalyst
loading in Fig. 7. It demonstrates that the rates are directly propor-
tional to catalyst loading based on the entire liquid phase volume,
due to proportional increase in the number of active sites.
For a spherical particle, the particle surface area per unit liquid
volume, aP, is also proportional to w, the catalyst loading per unit
liquid volume. It is possible to calculate the values of [As] and [Bs].
For instance,
0
-0.5
-1
kSL-Aap{[A0] − [As]} = robs = 4.12 × 10−7mol cm−3 s−1
y = -3791.8x + 7.4078
-1.5
R2 = 0.9877
Thus, when the appropriate values are inserted, it is seen that
[AS] ≈ [A0] and [BS] ≈ [B0]. Thus, any further addition of the catalyst
is not going to be of any consequence for external mass transfer.
Further reactions were carried out with 0.04 g/cm3 catalyst
loading used in the standard reaction.
-2
-2.5
-3
3.6. Proof of absence of intra-particle resistance
-3.5
-4
An absence of intra-particle mass transfer resistance could be
well proved from the experimental data with different catalyst
particle sizes. But it can be done only with those catalysts, which
do not have uniform particle size. UDCaT-5 catalyst is sulfate pro-
moted zirconia catalyst and its mean particle size was 0.0125 cm.
-4.5
-5
According to the Weisz Prater criterion, the parameter CWP
,
0.0028 0.0029 0.0029 0.003 0.003 0.0031 0.0031 0.0032
which represents the ratio of the intrinsic reaction rate to intra-
particle diffusion rate, can be evaluated from the knowledge of
observed rate (robs), the particle radius (Rp), effective diffusivity
of the limiting reactant (De), and concentration of the reactant at
the external surface of the particle.
1/T
Fig. 10. Arrhenius plot (plot of ln k vs 1/T). Veratrole: 0.04 mol, propionic anhy-
dride: 0.2 mol, catalyst: UDCaT-5, catalyst loading: 0.04 g cm−3, speed of agitation:
1000 rpm.

G.D. Yadav, S.R. More / Applied Catalysis A: General 411–412 (2012) 123–130
129
3.9. Reusability of catalyst
0.05
The catalyst reusability was studied three times, including the
use of fresh catalyst. After each run, the catalyst was filtered,
washed with methanol, dried at 120 ◦C for 3 h, and weighed before
using in the next batch of reaction. There was some attrition of cat-
alyst particles during agitation. In a typical batch reaction, there
was an inevitable loss of particles during filtration due to attrition.
Although the catalyst was washed with methanol after filtration
to remove all adsorbed reactants and products, there was still a
possibility of retention of some amount of adsorbed reactants and
products which might cause the blockage of active sites of the cat-
alyst. The actual amount of catalyst used in the next batch, was
almost 5% less than the previous batch. There is only a marginal
decrease in conversion. When fresh amount of catalyst was added
to make up for the losses, there was no reduction in conversion and
yields, which showed that the catalyst was stable.
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
y = 0.0015x
R2 = 0.991
3.10. Development of kinetic model
0
10
20
30
40
The above results were used to build
The reaction involves two organic phase reactants, A (vera-
trole), (propionic anhydride), the desired product (3,4-
a kinetic model.
Time (min)
B
C
Fig. 11. Plot of ln(1 − XA) + [XA/(1 − XA)] vs time for M = 1.
methoxypropiophenone) and D (co-product propionic acid). Since
A and B are liquid phase reactants, they need to diffuse to the inte-
rior surface of the catalyst. The different steps involved in this
process are according to the Eley–Rideal mechanism, which was
found to hold for acid catalyzed acylation reactions [25,31].
The first step involves the formation of carbocation by the
adsorption of propionic anhydride on a catalytic site (S):
where kSR is the reaction rate constant.
The rate of reaction of veratrole per unit liquid volume is given
by
dCA
−
= kSRCACBS
(12)
dt
After substitution for CBS
.
dCA
dt
KBCBCS
CD
CBCACS
CD
k
a
−
= kSRCA
= (kSRKB)
(13)
(14)
(CH3CH2CO)2 O + H+ ꢀCH3CH2C+O +CH3CH2COOH
(8)
k
a
The total side balance is as follows,
(B)
(S)
(BS)
(D)
Ct = w = CBS + CAS + CS
The rate of chemisorption of B:
where w is the catalyst loading.
when CAS = 0, w = CBS + CS
ꢀ
ꢁ
w
ꢀ
−rB = kBCBCS − kB CBSCD
(9)
CS
=
(15)
(16)
1 + KBCB/CD
After substituting the CS in Eq. (13),
−rB = 0, at equilibrium (quasi equilibrium)
kBCBCS = kBꢀ CBSCD
dCA
dt
kSRKBwCBCA
−
=
= rA
(CD + KBCB)
(10)
CA = CA (1 − XA)
CB = CB − CA XA = CA (M − XA)
CD = CA XA
where CB /CA = M, initial mole ratio of propionic anhydride to
veratrole 0XA =0fractional conversion of A. Substituting in terms of
XA and integrating, the following equations are obtained.
(16a)
(16b)
(16c)
0
Since KB = kB/kBꢀ
0
0
0
0
CBCS
CBS = KB
CD
(11)
Now the reaction between the adsorbed B as BS and liquid-phase
reactant A takes place as follows,
COCH2CH3
OCH3
OCH3
kSR
+
BS
+
S
OCH3
OCH3
(C)
(A)

130
G.D. Yadav, S.R. More / Applied Catalysis A: General 411–412 (2012) 123–130
Scheme 1. Propionylation of veratrole to 3,4-dimethoxypropiophenone using UDCaT-5 as novel solid acid catalyst.
active, selective, stable and reusable catalyst. It gave 100% selec-
0.2
0.18
0.16
0.14
0.12
0.1
tivity towards the desired product 3,4-dimethoxypropiophenone.
The effects of various parameters on the rates over UDCaT-5 were
discussed. A kinetic model for the reaction mechanism was success-
fully developed. It follows Eley–Rideal type of mechanism, wherein
the chemisorbed propionic anhydride generates a carbocation and
propionic acid, and carbocation reacts with veratrole from the liq-
uid phase within the pore space. The energy of activation was found
to be 7.32 kcal/mol.
y = 0.0059x
R2 = 0.9843
y = 0.0039x
R2 = 0.9869
Acknowledgments
y = 0.0031x
R2 = 0.9884
0.08
0.06
0.04
0.02
0
G.D.Y. acknowledges support from Darbari Seth Professor
Endowment, R.T. Mody Distinguished Professor Endowment of ICT
and J.C. Bose National Fellowship of Department of Science and
Technology, Govt. of India. S.R.M. is thankful to World-Bank’s Tech-
nical Education Quality Improvement Program (TEQIP), for the
award of a Junior Research Fellowship & Research Grant during
this work.
y = 0.0021x
R2 = 0.9939
0
10
50° C
20
30
40
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Time (min)
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70° C
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=
(17)
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(1 − KB)
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Case (c): M =/ 1,
ꢂ
ꢃ
ꢂ
ꢃ
ꢂ
ꢃ
M
M − XA
kSRKB(M − 1)wt
KB(M − 1) + 1
− ln(1 − XA) +
ln
=
KB(M − 1) + 1
M
(19)
Case (d): for very small values of KB, KB(M − 1) + 1 ≈ 1
ꢂ
ꢃ
M − XA
− ln(1 − XA) + M ln
= kSRKB(M − 1)wt
(20)
M
These models were validated against the experimental data.
It was found that the adsorption of B was very weak (KB ꢂ 1)
and thus Eq. (18) for M = 1 (Fig. 11) and Eq. (20) for M =/ 1 (Fig. 12)
fit the data very well (Scheme 1).
4. Conclusion
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