Highly selective vapor-phase acylation of veratrole over H3PO4/TiO2-ZrO2: Using ethyl acetate as a green and efficient acylating agent

Article abstract of DOI:10.1002/cjoc.201090066

A simple sol-gel method with and without surfactant was applied to prepare TiO₂-ZrO₂ mixed oxides containing Ti and Zr at a molar ratio of 1:1. Several catalysts containing w=15%-35% H₃PO₄ were set up using these mixed oxides. The physical and chemical properties of catalysts were investigated by BET, SEM and pyridine adsorption-desorption. The catalytic performance of each material was determined for the vapor-phase acylation of veratrole (1,2-dimethoxybenzene) to 3,4-dimethoxyacetophenone (3,4-DMAP), which was found to be the major product of the reaction of veratrole with ethyl acetate, with alkylated products being the minor products. 2,3-Dimethoxyacetophenone (2,3-DMAP) was not detected in the product stream. In the best experimental conditions, the alkylated products were less than 0.7%. This reaction may represent an environmentally friendly alternative to use the ethyl acetate as the acylating reagent. The feed molar ratios of veratrole/ethyl acetate were varied over a wide range of 0.1 to 1, and the optimum feed ratio of veratrole/ethyl acetate was 1:3. Space velocity employed in the veratrole acylation reported as WHSV (veratrole) was 1.2 h^-1. The acylation reactions were carried out in the temperature range of 423 to 673 and the optimum H₃PO₄ content for acylation was w15%.

Full text of DOI:10.1002/cjoc.201090066

FULL PAPER
Highly Selective Vapor-Phase Acylation of Veratrole over
H3PO4/TiO2-ZrO2: Using Ethyl Acetate as
a Green and Efficient Acylating Agent
Javad Kalbasi, Roozbeh*,a,b
Massah, Ahmad Rezaa,b
Abbaspourrad, Alireza*,c
Zamani, Farzada,b
a Department of Chemistry, Islamic Azad University, Shahreza Branch, 311-86145, Shahreza, Isfahan, Iran
b Razi Chemistry Research Center, Islamic Azad University, Shahreza Branch, Shahreza, Isfahan, Iran
c
Department of Chemistry, Islamic Azad University, Shahryar-Qods City Branch, 37515-374,
Qods City, Tehran, Iran
A simple sol-gel method with and without surfactant was applied to prepare TiO2-ZrO2 mixed oxides containing
Ti and Zr at a molar ratio of 1∶ 1. Several catalysts containing w＝ 15%— 35% H3PO4 were set up using these
mixed oxides. The physical and chemical properties of catalysts were investigated by BET, SEM and pyridine ad-
sorption-desorption. The catalytic performance of each material was determined for the vapor-phase acylation of
veratrole (1,2-dimethoxybenzene) to 3,4-dimethoxyacetophenone (3,4-DMAP), which was found to be the major
product of the reaction of veratrole with ethyl acetate, with alkylated products being the minor products.
2,3-Dimethoxyacetophenone (2,3-DMAP) was not detected in the product stream. In the best experimental condi-
tions, the alkylated products were less than 0.7%. This reaction may represent an environmentally friendly alterna-
tive to use the ethyl acetate as the acylating reagent. The feed molar ratios of veratrole/ethyl acetate were varied
over a wide range of 0.1 to 1, and the optimum feed ratio of veratrole/ethyl acetate was 1∶ 3. Space velocity em-
ployed in the veratrole acylation reported as WHSV (veratrole) was 1.2 h－ 1. The acylation reactions were carried
out in the temperature range of 423 to 673 K and the optimum H3PO4 content for acylation was w＝ 15%.
Keywords vapor-phase acylation, veratrole, ethyl acetate, 3,4-dimethoxyacetophenone, environmentally friendly
Introduction
backs can be overcome using recoverable and regener-
able solid catalysts. Solid catalysts are easy to recover
and overcome corrosion problems. Therefore, they
could replace conventional catalysts and these processes
fit well in the domain of environmentally benign chem-
istry.
Friedel-Crafts acylation is one of the most important
methods for the synthesis of aromatic ketones,1-5 which
are important intermediates for the production of phar-
maceuticals, dyes, agrochemicals and fragrances. Acy-
lation of anisole and veratrole (1,2-dimethoxybenzene)
leads to the synthesis of p-acetoanisole and acetovera-
trole, respectively.6 Moreover, acetoveratrole is used for
the synthesis of papaverine, an opium-alkaloid anti-
spasmodic.7
Acylation of aromatic compounds has traditionally
been carried out using homogeneous acid catalysts such
as AlCl3, FeCl3, ZnCl2, HF, etc.8-10 Unfortunately, the
use of conventional catalysts is associated with a lot of
problems. A major drawback of these catalysts is that
they are non-regenerable. Moreover, more than a
stoichiometric amount of the catalyst is needed to carry
out an experiment. Not only the work-up steps involve
hydrolysis of the resultant intermediate complexes, but
also a large amount of hazardous waste products is pro-
duced. Disposal of such waste products also leads to
other environmental problems. Many of these draw-
During the past few years, different solid acid cata-
lysts such as zeolites,11-13 metal cation exchanged
clays,14 ion exchange resins,15 supported-heteropoly-
acids,7 WOx/ZrO2,16 sulphated zirconia/MCM-41,17
nano-sized TPA/ZrO2 dispersed in SBA-15 channels,18
TPA/SBA-1519 and TPA/ZrO2 dispersed in MCM-41
channels20 have been used for the acylation of veratrole.
However, catalyst deactivation and low conversion or
selectivity are problems associated with these reagents.
Mixed-metal oxides are heterogeneous catalysts that
have been less investigated for the acylation of aromatic
substrates. Transition metal oxides can be used as cata-
lysts alone or in combination during vapor-phase cata-
lytic reactions. It is believed that a mixture of oxides
brings out a combined effect or a sort of synergistic be-
havior enhancing the catalytic activity.21,22 Metal oxides
such as ZrO2, TiO2, Fe2O3 and Zr containing mixed ox-
*
E-mail: rkalbasi@iaush.ac.ir (R. J. Kalbasi); abbaspour@alumni.iut.ac.ir (A. Abbaspourrad); Tel.: 0098-0321-3292072; Fax: 0098-0321-3293095
Received April 20, 2009; revised July 20, 2009; accepted September 4, 2009.
Chin. J. Chem. 2010, 28, 273— 284
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273

Javad Kalbasi et al.
FULL PAPER
ides become highly acidic on modification with anions
such as SO24− , PO34− , etc.23 To overcome the technical
and enviro-economic problems associated with liquid
acids, these solid acid catalysts have been employed in
several industrially important acid catalyzed reactions
such as low temperature isomerization, alkylation, es-
terification, cracking, etc.24-27 Recently we observed that
H3PO4/TiO2-ZrO2 showed high thermal stability, low
catalytic deactivation and very good selectivity for va-
por-phase Beckmann rearrangement,28 Fries rearrange-
ment29 and phenol acylation.30
Various reagents have been used for acylating aro-
matic compounds. Chiche et al.31 studied the acylation
of toluene and p-xylene with straight-chain carboxylic
acids catalyzed by CeNa-Y zeolites in liquid phase.
Singh and Pandey32 reported the formation of aceto-
phenone by the reaction of benzene with acetic acid
over zeolite. The electrophilic acylation of methoxy-
benzene (anisole) was studied using phenylacetyl chlo-
ride,33,34 phenylpropionyl chloride,33 acetyl chloride,35
acetic anhydride11-20 and phenylacetic and phenylpropi-
onic acids.33
thoroughly mixed. Then the solution was cooled down
to room temperature, and H-acetylacetone was added as
the complexing agent. This clear solution was divided in
two parts. The first portion was hydrolyzed with deion-
ized water (11.0 mol of H2O/mol of alkoxide), and the
second portion was hydrolyzed with deionized water
containing cetylpyridinium bromide (CPB) surfactant
(mol of surfactant/mol of alkoxide＝0.1). The solutions
were left overnight to hydrolyze the alkoxides, yielding
transparent gels, which were dried at 110 ℃ to remove
water and solvent, and then calcined at 500 ℃ for 5 h
to remove the organics. Supports are denoted as
TiO2-ZrO2(1∶1), and TiO2-ZrO2(1∶1)-surf. A series
of catalysts with varying H3PO4 contents were prepared
by impregnating calculated amounts of H3PO4 dissolved
in deionized water on TiO2-ZrO2 supports. The phys-
ico-chemical characterization of the catalysts is found in
our previous report.28
We have measured the phosphorous content in both
catalysts w＝15% H3PO4/TiO2-ZrO2-surf and w＝15%
H3PO4/TiO2-ZrO2. There was no significant difference
between phosphorous contents of the two mixed-oxides.
Moreover, there is no significant loss (less than 5%) of
H3PO4 after calcinations and baking the surfactant from
the mixed-oxide. Pyridine was used as a probe molecule
to distinguish between Brønsted and Lewis acid sites.42
The catalytic experiments were carried out under
atmospheric pressure in a flow Pyrex reactor (i.d. 8 mm)
containing 0.5 g of catalyst (20—40 mesh). A mixture
of veratrole and ethyl acetate was passed into the reactor
Unfortunately, the use of acetic anhydride and chlo-
ride is associated with a lot of environmental and corro-
sion problems.
Recently, the feasibility of both alkylation and acy-
lation with esters such as methyl acetate, ethyl acetate,
isopropyl acetate and tert-butyl acetate has been re-
ported.36-41
In the work to be discussed in the present paper, we
set out to investigate one of the simplest and most selec-
tive vapor-phase acylations. The reaction takes place
between ethyl acetate and veratrole, on w ＝ 15%
H3PO4/TiO2-ZrO2(1 ∶ 1) and w ＝ 15% H3PO4/TiO2-
ZrO2(1∶1)-surfactant.
at WHSV in the range of 0.3—2.4 h－ and in the tem-
1
perature range of 423—673 K.
The veratrole was dissolved in the ethyl acetate
(with various molar ratios) and fed into the reactor with
an infusion pump (GENIE, Kent Scientific Corporation).
Before each run of the reaction, the catalyst was pre-
heated at 723 K for 1 h in a flow of dry nitrogen (50
mL/min). The material balance during the initial 30 min
of reaction was poor. Therefore, the first 30 min was
deducted for the reaction time on stream (TOS). Subse-
quently, products were collected from the reactor each
hour in an ice/water trap and analyzed off-line using a
Shimadzu gas chromatograph, equipped with a wide
bone OV-17 (60 m) capillary column and an FID detec-
tor.
The catalysts were prepared with and without sur-
factant to evaluate and correlate their catalytic activity.
The catalytic activity of the best catalyst [w＝15%
H3PO4/TiO2-ZrO2(1∶1)-surf] was studied as a function
of different reaction parameters. In the presence of this
catalyst and with ethyl acetate as an environmental
friendly acylating agent that has not any corrosion
problem, excellent activity and high 3,4-dimethoxy-
acetophenone selectivity (＞99%) were obtained. There
is an advantage of little formation of alkylating product,
which is a major product in the presence of MCM-41
and Al-MCM-41 with ethyl acetate as an acylating
agent.37,38 Furthermore, the catalyst could be easily re-
generated by thermal treatment without any appreciable
decrease in the activity, and selectivity towards
3,4-dimethoxyaceto-phenone.
Fourier transform IR spectra of adsorbed pyridine
were measured using a JASCO FT/IR (680 plus) spec-
trometer.30 Approximately 40—50 mg of material that
had been calcined in air for 4 h at 500 ℃ was pressed
(for 3 min at 1470997.5 kPa pressure under approxi-
mately 10－ 2 torr vacuum) into a self supporting wafer of
15 mm diameter. The pretreated wafer was conducted
with 3.46 kPa of pyridine at 473 K for 1 h and evacu-
ated at 473, 573 and 673 K for 1 h in dynamic vacuum.
After each treatment, an IR spectrum was recorded at
room temperature. The peak area values corresponding
to adsorbed pyridine related to Lewis and Brønsted acid
Experimental
Appropriate amounts of zirconium propoxide and ti-
tanium n-butoxide were dissolved in n-butanol to pre-
pare the TiO2-ZrO2-surf, and TiO2-ZrO2 catalysts. The
solution was heated up to 60 ℃. The components were
－
1
sites were collected at 1445 and 1545 cm , respectively.
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Highly Selective Vapor-Phase Acylation of Veratrole
The relative peak areas were calculated for all catalysts
(Table 1, presenting the surface area of the catalysts).
Results and discussion
Characterization of the catalyst
The nature of acidic sites in TiO2-ZrO2(1∶1) and
TiO2-ZrO2(1 ∶ 1)-surf as supports and in w ＝ 15%
H3PO4/TiO2-ZrO2(1 ∶ 1) and w ＝ 15% H3PO4/TiO2-
ZrO2(1∶1)-surf, as the best catalysts, was determined
by FTIR pyridine adsorption study (Figure 1). Corre-
sponding values are reported in Table 1.
As depicted in Figure 1 absorption bands around
1605, 1575, 1490 and 1444 cm－ in both spectra show
1
Lewis acid sites, which can be observed for both sup-
ports and catalysts. However, Brønsted acid band (1540
－
1
cm ) is not observed in supports. It is worthy to men-
tion that weak bands in 1540 cm－ 1 (Figure 1, lines c and
d) are due to the negligible concentration of Brønsted
sites in the catalysts, especially in the best catalyst (Ta-
ble 1).
The N2 adsorption-desorption isotherms of TiO2-
ZrO2(1∶1)-surf and w＝15% H3PO4/TiO2-ZrO2(1∶
1)-surf samples are shown in Figure 2, which are similar
to the Type IV isotherms according to the characteristic
of mesoporous materials44 in IUPAC classification.
From the two branches of adsorption-desorption iso-
therms, the presence of a sharp adsorption step in the
p/p0 region from 0.4—0.8 and a hysteresis loop at the
relative pressure p/p0＞0.7 shows that the materials
posses a well defined array of regular mesopores. The
specific area and the pore size have been calculated us-
ing Brunauer-Emmett-Teller (BET) and Barrett-Joyner-
Halenda (BJH) methods, respectively.
Figure 1 (A) (a) Pyridine desorption on TiO2-ZrO2(1∶1)-surf
at 200 ℃; (b) pyridine desorption on TiO2-ZrO2(1/1)-surf at 300
℃; (c) pyridine desorption on w＝15% H3PO4/TiO2-ZrO2(1∶1)-
surf at 200 ℃; (d) pyridine desorption on w＝15% H3PO4/TiO2-
ZrO2(1∶1)-surf at 300 ℃. (B) FTIR spectra of (a) pyridine de-
on TiO2-ZrO2(1∶1) at 300 ℃; (c) pyridine desorption on w＝
15% H3PO4/TiO2-ZrO2(1∶1) at 200 ℃; (d) pyridine desorption
on w＝15% H3PO4/TiO2-ZrO2(1∶1) at 300 ℃.
The structural data for all these materials, [TiO2-
ZrO2(1∶1)-surf, w＝15% H3PO4/TiO2-ZrO2(1∶1)-surf,
TiO2-ZrO2(1∶1) and w＝15% H3PO4/TiO2-ZrO2(1∶
1)], including BET surface area, total pore volume, and
pore size, are summarized in Table 2. The mixed oxide
◦
sorption on TiO2-ZrO2(1∶1) at 200 C; (b) pyridine desorption
Table 1 Acidity and surface area of the catalysts
Amount of acid sites/(mmol•kg－
)
1
1
Catalyst
Temperature/K
Surface area/(m2•g－
237
)
Brønsted
Lewis
473
573
673
—
—
—
47.0
16.0
5.4
TiO2-ZrO2
473
573
673
5.5
3.0
2.2
71.0
44.0
13.0
w＝5% H3PO4/TiO2-ZrO2
w＝15% H3PO4/TiO2-ZrO2
213
201
473
573
673
11.0
6.0
170.0
101.0
71.0
4.5
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Javad Kalbasi et al.
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Continued
Amount of acid sites/(mmol•kg－
)
1
1
Catalyst
Temperature/K
Surface area/(m2•g－
)
Brønsted
Lewis
473
573
673
31.0
17.0
11.0
216.0
134.0
95.0
w＝ 25% H3PO4/TiO2-ZrO2
188
473
573
673
—
—
—
53.0
29.0
11.0
w＝ 35% H3PO4/TiO2-ZrO2
TiO2-ZrO2-surf
150
270
246
221
473
573
673
1.5
0.1
—
79.0
50.0
18.5
473
573
673
3.0
0.5
0.2
178.0
149.0
83.0
w＝ 5% H3PO4/TiO2-ZrO2-surf
w＝ 15% H3PO4/TiO2-ZrO2-surf
473
573
673
8.7
2.0
1.1
207.0
156.0
98.0
473
573
673
11.5
5.4
230.0
168.0
106.0
w＝ 25% H3PO4/TiO2-ZrO2-surf
w＝ 35% H3PO4/TiO2-ZrO2-surf
192
165
4.3
473
573
673
31.0
17.0
11.0
216.0
134.0
95.0
Table 2 Porosity data of TiO2-ZrO2(1∶ 1)-surf, w＝ 15% H3PO4/TiO2-ZrO2(1∶ 1)-surf, TiO2-ZrO2(1∶ 1) and w＝ 15% H3PO4/
TiO2-ZrO2(1∶ 1)
1
1
Sample
BET surface area/(m2•g－
)
VP/(cm3•g－
)
DP/nm
16.0
9.61
2.5
TiO2-ZrO2(1∶ 1)-surf
270
221
237
201
0.55
w＝ 15% H3PO4/TiO2-ZrO2(1∶ 1)-surf
TiO2-ZrO2(1∶ 1)
0.28
0.20
w＝ 15% H3PO4/TiO2-ZrO2(1∶ 1)
0.09
0.7
prepared with surfactant [TiO2-ZrO2(1∶1)-surf and
w＝15% H3PO4/TiO2-ZrO2(1∶1)-surf] showed higher
surface area, pore volume and average pore diameter
than that prepared without surfactant [TiO2-ZrO2(1∶1)
and w＝15% H3PO4/TiO2-ZrO2(1∶1)] (Table 2), which
is probably due to the formation of wider pores in the
presence of surfactant. It is known that calcined
TiO2-ZrO2(1∶1)-surf has a high BET surface area (270
m2/g), a large pore volume (0.55 cm3/g) and pore size
(16 nm), which is indicative of its potential application
as a host in H3PO4. After treatment with H3PO4, it ex-
hibits a smaller specific area, pore size and pore volume
than the pure TiO2-ZrO2(1∶1)-surf, which might be due
to the presence of H3PO4 on the pore surface. Although
these textural properties are smaller than those found for
TiO2-ZrO2(1∶1)-surf, w＝15% H3PO4/TiO2-ZrO2(1∶
1), it is still suitable for acylation of veratrole.
The morphologies of calcined solid TiO2-ZrO2(1∶
1)-surf and w＝15% H3PO4/TiO2-ZrO2(1∶1)-surf are
presented in Figure 3. SEM images show the external
morphology of the solid which consists of spherical ag-
glomerates with sizes of 30—70 nm (Figures 3a and 3b).
The phosphoric acid layer on TiO2-ZrO2(1∶1)-surf can
be seen in Figures 3c and 3d.
3.2 Catalytic activity
The acylation of veratrole with ethyl acetate has been
studied over H3PO4/TiO2-ZrO2(1∶1) in the presence
and absence of surfactant. The products were mainly
3,4-dimethoxyacetophenone (99.3%) with
amount of alkylated products (0.7%).
a trace
The difference between ZrO2-TiO2 and ZrO2-TiO2-
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Chin. J. Chem. 2010, 28, 273— 284

Highly Selective Vapor-Phase Acylation of Veratrole
According to Pandurangan and coworkers,41 strong
acid sites cause the formation of alkyl cation. Hence, the
catalysts containing strong acid sites in interaction with
ester produce the alkyl cation and alkylated product. On
the other hand, weak interaction with ester due to the
weak acid sites is responsible for the formation of acetyl
cation and therefore acylated products.
According to our previous work28 the surface area of
the mixed oxide prepared in the presence of surfactant
and loaded with H3PO4 is about 10% higher than those
of the other samples. For instance, the surface areas of
the w＝15% H3PO4/TiO2-ZrO2(1∶1) and w＝15%
－1
H3PO4/TiO2-ZrO2(1∶1)-surf are 201 and 221 m2•g ,
respectively. Interestingly, these mixed oxides show
higher selectivity and activity in the optimized condi-
tions. It should also be mentioned that in all of the
mixed oxides prepared in the absence of surfactant and
loaded with H3PO4, there are some crystalline phases
(anatase crystalline phase of TiO2 and tetragonal crys-
talline phase of ZrO2). However, for the catalysts pre-
pared in the presence of surfactant the XRD pattern of
the best catalyst, i.e., w＝15% H3PO4/TiO2-ZrO2(1∶1)-
surf is amorphous, similar to the XRD pattern of the
parent mixed oxide.28
Figure 2 Nitrogen adsorption isotherms at 77 K for (a) TiO2-
ZrO2(1/1)-surf and (b) w＝ 15% H3PO4/TiO2-ZrO2(1∶ 1)-surf.
It is known43 that pure TiO2 and ZrO2 have a broad
acid site distribution. On the other hand, the NH3-TPD
desorption curve corresponding to the TiO2-ZrO2 mixed
oxides is characteristic of solids having a sharp acid site
distribution. The nature of catalyst acid site is reported
in Table 1. Brønsted acid sites are not observed in the
supports, however, the available Brønsted acid sites in
the catalysts, especially in the best catalyst, are negligi-
ble. Both the alkylation and acylation reactions can be
related to the nature of acid sites in the catalyst.
According to Tanabe’s hypothesis,45 the surface
structure of TiO2-ZrO2 can be represented as (I) and (II)
in Scheme 1. Both structures (I) and (II) contain Lewis
acidic and basic sites. So it can be seen that ZrO2-TiO2
and ZrO2-TiO2-surf just show Lewis acid sites and
Brønsted acid sites are not available (Table 1). On the
other hand, with loading H3PO4 on these supports two
things happened: some of loaded H3PO4 cause removing
of the adsorbed water on the Lewis sites (structures I
and II), which leads to＋increasing Lewis acid sites of the
that loaded by esterification of remaining M—OH
groups on the support lead to producing weak Brønsted
acid sites (P—OH). According to the data presented in
Table 1, we can see that with increasing amount of
H3PO4 loaded on the surface of supports, Lewis acid
sites increase drastically by removing the adsorbed wa-
ter on the Lewis sites (structures I and II). However,
Brønsted acid sites increase slightly (the phosphoric
acid interacts with the more basic hydroxyl group of the
support and new structures are formed as shown in III,
IV, V and VI), although these Brønsted acid sites are
weak (P—OH) and have not much effect on the total
acidity of the catalyst. According to the data presented
Figure 3 SEM micrographs of samples at different magnifica-
tions: (a) TiO2-ZrO2(1∶ 1)-surf, (b) TiO2-ZrO2(1∶ 1)-surf, (c)
w＝ 15% H3PO4/TiO2-ZrO2(1∶ 1)-surf, (d) w＝ 15% H3PO4/TiO2-
ZrO2(1∶ 1)-surf.
surf is in their different porosity. When the sol-gel
process was done in the presence of surfactant, polym-
erization was done around the surfactant as a huge and
directing agent. Afterward, by calcinations of this sup-
port at about 550 ℃, the surfactant molecules would be
removed from the surface completely and results in
producing pores in the support structure. Therefore, the
ZrO2-TiO2-surf shows a mesoporous structure, high se-
lectivity and large surface area because of these pores
(Figure 2 and Tables 1 and 2). On the other hand,
ZrO2-TiO2 has less pores and surface area because there
is not any surfactant in the sol-gel process. So the reac-
tion was done mainly on the external surface of the
catalyst and we would see lower selectivity for this
support. Above explanations can be approved by BET
results (Figure 2 and Table 2).
＋
obtained catalyst (Zr4 and Ti4 ). Some other H3PO4
Chin. J. Chem. 2010, 28, 273— 284
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277

Javad Kalbasi et al.
FULL PAPER
in Table 1, it can be seen that the structures I and II are
much more than structures III, IV, V and VI (w＝5%
H3PO4/TiO2-ZrO2 and w＝15% H3PO4/TiO2-ZrO2). It is
obvious that with increasing the loaded H3PO4 on the
surface of the support, the contribution of structures III,
IV, V and VI increases and so the Bronsted acid sites
will increase (w＝5% H3PO4/TiO2-ZrO2 and w＝15%
H3PO4/TiO2-ZrO2).
Scheme 2 Mechanism for acylation of veratrole with ethyl ace-
tate over H3PO4/TiO2-ZrO2-surf
Scheme 1 A schematic presentation of TiO2-ZrO2 structures
and interaction with H3PO4
H3PO4 on the surface of catalyst, for veratrole conver-
sion and product selectivity was investigated.
The results indicate that the activity of the unloaded
TiO2-ZrO2 is lower than the activities of all H3PO4
loaded catalysts between 423 and 673 K. Hence, H3PO4
incorporation on the TiO2-ZrO2 has a significant role in
activating the catalysts during the acylation of veratrole.
The results presented in Table 3 show the low selectiv-
ity to 2,3-dimethoxyacetophenone, alkylated and di-ac-
ylated products when the reaction was conducted on the
H3PO4/TiO2-ZrO2(1∶1). Whereas, when the reaction
was run over the w＝15% H3PO4/TiO2-ZrO2 (1∶1)-surf,
3,4-DMAP produced with high selectivity (99.3%).
By increasing the phosphorous content of the best
support i.e., TiO2-ZrO2(1∶1)-surf, from 0 to w＝15%,
3,4-DMAP selectivity decreased from 100% to 99.3%,
but veratrole conversion increased from 15.7% to 91.1%.
As a result the w＝15% H3PO4/TiO2-ZrO2(1∶1)-surf
catalyst shows a good veratrole conversion and good
selectivity to 3,4-DMAP in this condition.
Therefore, we can conclude that the surface of the
catalyst has some weak Brønsted acid sites (P—OH)
available for the acylation reaction.
Formation of acylated products requires nucleophilic
attack of veratrole on the acyl group of the ethyl acetate
as shown in Scheme 2. It is clear that ethyl acetate pre-
fers to be activated by donating electron from softer
oxygen atom of the alkoxy group of the ester to the soft
＋
＋
Lewis acid sites (Ti4 or Zr4 ). This is in contrast with
the fact that surface of the catalyst contains strong
＋
Brønsted acid sites or hard Lewis acid sites like Mg2 .36
So the ester is activated through the oxygen atom of the
acyl group.
Effect of loaded H3PO4 on the catalytic activity
According to Dalai et al.,46 sulfate groups generate
strong Lewis and Brønsted acidity when adsorbed on the
TiO2-ZrO2 mixed oxide surface. As we stated above, the
acidity of H3PO4 is milder than that of H2SO4, thus it
would be expected that H3PO4/TiO2-ZrO2 showed
higher selectivity to acylated products than alkylated
ones. Hence, we decided to investigate the catalytic ac-
tivity of H3PO4/TiO2-ZrO2 mixed oxide in acylation of
veratrole. Our recent work showed that H3PO4/TiO2-
ZrO2 had high thermal stability, low catalytic deactiva-
tion and very good selectivity for vapor-phase Beck-
mann rearrangement, Fries rearrangement and acylation
of phenol.28-30 So, to the best of our knowledge it is the
first work on the effect of weight percentage of loaded
Effect of temperature on the catalytic activity
The results of veratrole acylation using ethyl acetate
over w＝15% H3PO4/TiO2-ZrO2(1∶1)-surf and w＝
15% H3PO4/TiO2-ZrO2(1∶1) at different temperatures
are given in Figure 4. The conversion of veratrole to
3,4-dimethoxyacetophenone (3,4-DMAP) in both cases
was low (32.5% and 27.6%) at 423 K and attained to
91.1% and 84.0% at 573 K, respectively. Conversion
increases by raising the temperature from 423 to 623 K,
and decreases at 673 K, as soon as veratrole competes
278
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© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 273— 284

Highly Selective Vapor-Phase Acylation of Veratrole
Table 3 Effect of loaded H3PO4 on the activity of H3PO4/TiO2-ZrO2(1∶1) and H3PO4/TiO2-ZrO2(1∶1)-surfa
Product selectivity/%
Conversion of
Catalyst
w(H3PO4)/%
Di-acylated
product
veratrole/%
3,4-DMAP
2,3-DMAP
Alkylated product
0
15.7
63.9
91.1
93.0
93.4
100
99.5
99.3
95.3
90.4
ND*
ND
ND
0.8
ND
ND
ND
0.1
0.7
ND
0.5
0.7
3.8
7.9
5
15
25
35
H3PO4/TiO2-ZrO2(1∶1)-surf.
1.0
0
11.3
59.1
84.0
87.0
89.2
100
97.1
94.1
83.0
77.2
ND
0.7
1.1
1.4
1.8
ND
ND
ND
0.4
1.9
ND
2.2
5
H3PO4/TiO2-ZrO2(1∶1)
15
25
35
4.8
15.2
19.1
a Reaction conditions: T＝573 K, flow rate＝20 mL•min－ 1, n(veratrole)∶n(ethyl acetate)＝1∶3, WHSV＝1.2 h－ 1, TOS＝1 h. ND: not
detectable.
of the catalyst. At lower temperature, veratrole is ad-
sorbed on the Lewis acid sites rather than ethyl acetate,
resulting in low conversion. Veratrole can be adsorbed
on the catalyst surface by O lone pair of OMe group
with Lewis acid sites or by charge transfer interaction
between the aromatic ring and Bronsted acid sites.50
H3PO4/TiO2-ZrO2(1∶1)-surf shows some weak Brøn-
sted acid sites (P—OH) but many Lewis acid sites. Thus
veratrole can be only adsorbed on catalyst surfaces by O
lone pair of OMe group. At higher temperatures,
veratrole can be easily desorbed, thus facilitating ad-
sorption of ethyl acetate. This has been observed up to
623 K. At 673 K, the conversion is low due to blocking
most active sites by coke.
The selectivity to 3,4-dimethoxyacetophenone de-
creased with increasing temperature. Higher temperature
reduces chemisorption of ethyl acetate on weak acid
sites, increases alkylation products and reduces forma-
tion of 3,4-dimethoxyacetophenone.
Ethyl acetate is free to chemisorb on all the acidic
sites. The electrophilic attack of ethyl cation is ac-
counted for by assuming the chemisorption of ethyl
acetate on strong acid sites. If chemisorption occurs on
weak acidic sites, it can not promote ethylation but can
promote only acylation.
At high temperatures, in addition to reduced chemi-
sorption of veratrole, there is blockage of active sites by
coke. Hence, the reaction of veratrole with acylium
cation can occur only in the vapor-phase and more
di-acylated products can be seen. Generation of more
ethyl cations at high temperature will result in more al-
kylated products. From these results it can be concluded
that, when the acylation of veratrole was carried out at
Figure 4 Effect of the reaction temperature on veratrole con-
version and product selectivity over H3PO4/TiO2-ZrO2(1∶1)-surf
(a) and H3PO4/TiO2-ZrO2(1∶1) (b). Reaction conditions: H3PO4
w＝15%, WHSV＝1.2 h－ 1, flow rate＝20 mL•min－
feed ratio＝1∶3 [n(veratrole)∶n(ethyl acetate)], TOS＝1 h.
,
1
573 K over w＝15% H3PO4/TiO2-ZrO2(1∶1)-surf, the
veratrole conversion was appropriate and selectivity to
3,4-dimethoxyacetophenone was highest.
with ethyl acetate for adsorption on the Lewis acid sites
Chin. J. Chem. 2010, 28, 273— 284
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
279

Javad Kalbasi et al.
FULL PAPER
Effect of feed ratio on the catalytic activity
－1
drastic decrease in conversion at 2.4 h , might be due
to the diffusion of veratrole through the surfaces of the
catalyst without having too much chance to react with
acylium ions. The 3,4-DMAP sele－ctivity increased with
The influences of the molar ratio of veratrole to ethyl
acetate on the activity and selectivity of w ＝15%
H3PO4/TiO2-ZrO2(1∶1)-surf were also studied at 573 K.
Figure 5 shows the veratrole conversion and product
selectivity of the reaction using 1∶1, 1∶2, 1∶3, 1∶5
and 1∶10 molar ratios of veratrole to ethyl acetate. The
conversion increased with increasing the ethyl acetate in
the feed ratio. At the 1∶3 feed ratio, the veratrole con-
version was about 91.9%. This reveals that at low feed
ratios (1∶1 and 1∶2) veratrole is highly adsorbed on
the acid sites of the catalyst in comparison with ethyl
acetate. As the reaction depends on the formation of
acetyl cation (or protonated ester), the conversion in-
creases with increasing ethyl acetate in the feed ratio
(1∶3, 1∶5 and 1∶10). Selectivity to 3,4-dimeth-
oxyacetophenone also increased with an increase in the
feed ratio. Interestingly, the maximum selectivity to
3,4-dimethoxyacetophenone was observed for the 1∶3
feed ratio. However, a decrease in selectivity to 3,4-di-
methoxyacetophenone was observed when the molar
ratios of veratrole to ethyl acetate were 1∶5 and 1∶10.
At high feed ratios (high percentage of ethyl acetate)
multi-acylation occured predominantly. It was found
that the reaction system with n(veratrole)∶n(ethyl ace-
tate)＝1∶3 is the most suitable condition for mono-
acylation of veratrole over w＝15% H3PO4/TiO2-ZrO2
(1∶1)-surf.
1
increasing the WHSV from 0.3 h and rea－ched to its
1
maximum value (99.3%－) at WHSV＝1.2 h and de-
1
creased again up to 2.4 h . So we selected WHSV＝1.2
－1
h
as optimum space velocity in our experiments.
Figure 6 Effect of WHSV on veratrole conversion and product
selectivity over H3PO4/TiO2-ZrO2(1∶1)-surf. Reaction condi-
tions: T＝573 K, H3PO4 w＝15%, flow rate＝20 mL•min－ 1, feed
ratio＝1∶3 [n(veratrole)∶n(ethyl acetate)], TOS＝1 h.
Effect of carrier gas flow rate on the catalytic activity
The influence of carrier gas flow rate on veratrole
conversion and selectivity of 3,4-DMAP acylation reac-
tion under constant injection rate of starting material
(constant WHSV) is shown in Figure 7. Increasing the
flow rate of nitrogen, and accordingly reducing the
residence time of reactants and products over the cata-
lyst, show a decrease in the selectivity to3,4-DMAP and
Figure 5 Effect of feed ratio on veratrole conversion and prod-
uct selectivity over H3PO4/TiO2-ZrO2(1∶1)-surf. Reaction con-
ditions: T＝573 K, H3PO4 w＝15%, flow rate＝20 mL•min－
WHSV＝1.2 h－ 1, TOS＝1 h.
,
1
Effect of WHSV on the catalytic activity
The acylation of veratrole was carried out with
different veratrole space velocities (0.3, 0.6, 1.2, 1.8 and
－1
2.4 h ) at 573 K with the feed ratio of veratrole∶ethyl
acetate＝1∶3 over w＝15% H3PO4/TiO2-ZrO2(1∶
1)-surf. The results are summarized in Figure 6. It was
found that the conversion decreased from 95.8% to
52.1% over w ＝15% H3PO4/TiO2-ZrO2(1 ∶1)-surf
Figure 7 Effect of carrier gas flow rate on veratrole conversion
and product selectivity over H3PO4/TiO2-ZrO2(1∶1)-surf. Reac-
tion conditions: T＝573 K, H3PO4 w＝15%, feed ratio＝1∶3
[n(veratrole)∶n(ethyl acetate)], WHSV＝1.2 h－ 1, TOS＝1 h.
Chin. J. Chem. 2010, 28, 273— 284
－1
when the WHSV increased from 0.3 to 2.4 h . The
280
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© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Highly Selective Vapor-Phase Acylation of Veratrole
in the conversion of veratrole and consequently an in-
crease toward 2,3-DMAP and di-acylated products. By
increasing the carrier gas flow rate and decreasing the
residence time, one can conclude that the reactant
molecules would have a smaller chance to pass through
the catalyst pores. Therefore, nitration occurs on the
external surface without shape selectivity, which results
in higher 2,3-DMAP selectivity. The 3,4-DMAP yield
was maximum when the carrier gas flow rate was 20
acylation of veratrole did not end up even after 10 h
on-stream. Accordingly, the H3PO4/TiO2-ZrO2-surf is
selective catalyst for producing 3,4-DMAP through the
acylation of veratrole, showing the good catalytic activ-
ity in this reaction.
－1
mL•min . If only the flow rate of carrier gas increases,
the partial pressure of the reactants decreases as well as
the residence time. Thus, lower conversion at higher
flow rate is quite expected.
Comparison among the acylating agents
The effect of acylating agents on the acylation of
veratrole with acetic anhydride, acetic acid and ethyl
acetate was studied. The results are presented in Figure
8. With acetic anhydride, the conversion of veratrole
was 100%, whereas, in the presence of acetic acid and
ethyl acetate the conversion of veratrole was 87.4% and
91.1%, respectively. Ethyl acetate showed very good
selectivity to 3,4-DMAP, however, use of acetic anhy-
dride and acetic acid showed a wide distribution of
by-products such as 2,3-DMAP, di-acylated and alkyl-
ated products with poor selectivity.
Figure 9 TOS for w＝15% H3PO4/TiO2-ZrO2(1∶1)-surf. Re-
action conditions: T＝573 K, WHSV＝1.2 h－ 1, flow rate＝20
mL•min－ 1, feed ratio, feed ratio＝1∶3 [n(veratrole)∶n(ethyl
acetate)].
The deactivated catalyst was heated up to 550 ˚C in
air. The XRD pattern of this sample was similar to the
fresh catalyst. The results indicate the structural stability
of the catalyst in the acidic medium of reaction.
Effect of support
The effect of support was studied over loaded w＝
15% H3PO4 on TiO2-ZrO2-surf, Al2O3, SiO2, SiO2-
Al2O3(1∶1), ZrO2, TiO2, ZrO2-Al2O3(1∶1) and TiO2-
SiO2(1∶1) at 573 K with ethyl acetate as the best acy-
－1
lating agent at WHSV＝1.2 h .
The use of zirconium oxide as a catalyst support has
several advantages over other conventional oxide sup-
ports such as alumina and silica, which can be listed as
follows: (1) It interacts strongly with the active phase;
(2) It possesses high thermal stability and is chemically
more inert than the conventional supported oxides; (3) It
is the only metal oxide, which may possess four chemi-
cal properties, namely acidity, basicity as well as the
reducing and oxidizing ability; (4) It displays super
acidic properties when modified with small quantities of
sulphate ions. The main problem associated with this
catalyst is the rapid loss of activity, which may be due to
coking and/or sintering. More active and stable catalysts
can be obtained by incorporating transition metals, es-
pecially noble metals into the ZrO2 system.48-50 So, the
thermal stability against sintering is also enhanced con-
siderably.51,52
Figure 8 Effect of acylating agents on veratrole conversion and
product selectivity over H3PO4/TiO2 ZrO2(1∶1)-surf. Reaction
conditions: T＝573 K, H3PO4 content w＝15%, flow rate＝20
mL•min－ 1, n(veratrole)∶n(acylating agent)＝1∶3, WHSV＝1.2
h－ 1, TOS＝1 h.
Effect of time on stream
The effect of time on stream was studied over w＝
According to Shibata’s report, the acidity of binary
metal oxides, especially TiO2-ZrO2, is higher than that
of single oxide such as TiO2, ZrO2, SiO2 and Al2O3.53
On the other hand, Al2O3 contains hard Lewis acid sites,
which according to previous explanation cause
producing alkylated products. To prove this idea we did
the reaction on the various supports. The results as pre-
sented in Table 4 show that in the presence of w＝15%
281
15% H3PO4/TiO2-ZrO2-surf at 573 K with ethyl acetate
－1
as the best acylating agent at WHSV＝1.2 h . The
study was conducted for 12 h and the results are pre-
sented in Figure 9. As shown, decrease in conversion
with increase in time-on-stream was observed. To some
extent, this might be due to the active site blockage of
catalyst by coke. Surprisingly, this study indicated that
Chin. J. Chem. 2010, 28, 273— 284
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de

Javad Kalbasi et al.
FULL PAPER
Comparison with other solid acid catalysts
H3PO4/TiO2-ZrO2(1∶1)-surf the selectivity to acylating
product was best.
Table 5 shows the comparison between the catalysts
used in the present study and other solid catalysts re-
ported in the literature for veratrole acylation.
Leaching studies of H3PO4/TiO2-ZrO2(1/1)-surf
No leaching of H3PO4 was observed from the cata-
lyst after 5 catalytic reaction cycles.
As can be seen from these data, the w＝15%
Table 4 Effect of support on veratrole conversion and product selectivitya
Product selectivity/%
Di-acylated
Catalyst
Conversion of veratrole/%
Alkylated
product
3,4-DMAP
2,3-DMAP
product
w＝15% H3PO4/TiO2-ZrO2(1∶1)-surf
w＝15% H3PO4/Al2O3
91.1
56.4
49.2
67.5
85.5
89.8
68.5
87.6
99.3
31.8
32.6
39.7
77.9
72.1
55.0
53.8
ND
12.5
8.4
ND
0.7
ND
55.7
59.0
50.0
7.2
w＝15% H3PO4/SiO2
ND
w＝15% H3PO4/SiO2-Al2O3(1∶1)
10.3
14.9
16.4
9.4
ND
w＝15% H3PO4/TiO2
ND
w＝15% H3PO4/ZrO2
ND
11.5
35.6
41.1
w＝15% H3PO4/TiO2-SiO2(1∶1)
ND
w＝15% H3PO4/ZrO2-Al2O3
5.1
ND
a Reaction conditions: T＝573 K, WHSV＝1.2 h－ 1, flow rate＝20 mL•min－ 1, feed ratio＝1∶3 [n(veratrole)∶n(ethyl acetate)], TOS＝1
h.
Table 5 Catalytic activity in the vapor phase reaction of veratrole with acylating agents over different catalyst
Conv. of Conv. of
acylating veratrole/
Selectivity/%
Temp./Time/ n(veratrole)/
Catalyst
Reagent
Ref.
7
℃
(liquid
phase)
h
n(acylatingagent)
3,4-DMAP 2,3-DMAP Di-acylated Alkylated
agent/%
%
60
Acetic
anhydride
DTP/HMS
2
1∶3
—
70.0
100
100
100
100
100
100
99.3
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.7
80
20% TPA/
SBA-15
Acetic
anhydride
(liquid
phase)
6
3
1
4
2
1
5∶1
20∶1
5∶1
2∶1
5∶1
1∶3
78.3
94.0
43.9
67.0
73
—
—
19
17
20
16
18
80
(liquid
phase)
Acetic
anhydride
SZ/MCM-41
w＝15% TPA/
w＝22.4% ZrO2/
MCM-41
80
(liquid
phase)
Acetic
anhydride
—
70
(liquid
phase)
w＝10% WO3/
Acetic
anhydride
—
ZrO2
w＝15% TPA/
w＝22.4% ZrO2/
SBA-15
60
(liquid
phase)
Acetic
anhydride
—
300
(vapor
phase)
w＝15% H3PO4/ Ethyl
This
work
—
91.1
TiO2-ZrO2-surf
acetate
282
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 273— 284

Highly Selective Vapor-Phase Acylation of Veratrole
Continued
Ref.
Conv. of Conv. of
acylating veratrole/
Selectivity/%
Temp./Time/ n(veratrole)/
Catalyst
Reagent
℃
(vapor
phase)
h
n(acylatingagent)
3,4-DMAP 2,3-DMAP Di-acylated Alkylated
agent/%
%
300
w＝15% H3PO4/ Ethyl
This
1
1∶3
—
84.0
94.1
100
100
1.1
—
—
—
—
—
4.8
—
—
TiO2-ZrO2
MWW
acetate
work
Acetic
anhydride
60
3
5
5∶1
79.2
—
—
54
55
60
(liquid
phase)
Acetic
anhydride
BEA (30)
12.5∶1
100
H3PO4/TiO2-ZrO2-surf catalyst shows high 3,4-DMAP
selectivity (99.3%), very low alkylated by-product and
excellent conversion for veratrole (91.1%) in the opti-
mum conditions.
2
3
Hoelderich, W. F. Catal. Today 2000, 62, 115.
Brunel, D.; Blanc, A. C.; Galarneau, A.; Fajula, F. Catal.
Today 2002, 73, 139.
Frank, H. G.; Stadehofer, J. W. Industrial Aromatic Chem-
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4
5
Conclusions
Zirconia-titania mixed oxides prepared in the pre-
ence and absence of surfactant and loaded H3PO4, dem-
onstrated surprisingly high stability and selectivity to-
wards acylation of veratrole with ethyl acetate. The
catalyst prepared in the presence of surfactant, w＝15%
H3PO4/TiO2-ZrO2(1∶1)-surf showed better selectivity
towards 3,4-DMAP than that prepared in the absence of
surfactant w＝15% H3PO4/TiO2-ZrO2(1∶1). In the
presence of this catalyst and with ethyl acetate as an
environmentally friendly acylating agent that have not
any corrosion problem, excellent activity and high
3,4-dimethoxyacetophenone selectivity (＞99%) were
obtained.
6
7
8
9
10 Kirk-Othmer Encyclopedia of Chemical Technology, Vol.
24, 5th ed., Wiley, New York, 1997, p. 38.
11 Guinard, C.; Pedron, V.; Richard, F.; Jacquot, R.; Spagnol,
M.; Coustard, J. M.; Perot, G. Appl. Catal. A: Gen. 2002,
234, 79.
12 Kantam, M. L.; Ranganath, K. V. S.; Sateesh, M.; Kumar, K.
B. S.; Choudary, B. M. J. Mol. Catal. A: Chem. 2005, 225,
15.
13 Moreau, P.; Finiels, A.; Meric, P. J. Mol. Catal. A: Chem.
2000, 154, 185.
In improved conditions, alkylated product was the
minor product. In this condition 2,3-DMAP was not
detected in the product stream. Furthermore, the catalyst
can be easily regenerated with a high recovery of the
initial activity.
The highest catalytic activity for acylation of vera-
trole with ethyl acetate was achieved over w＝15%
H3PO4/TiO2-ZrO2(1∶1)-surf catalyst. The highest se-
lectivity towards 3,4-DMAP was also found on w＝15%
H3PO4/TiO2-ZrO2(1∶1)-surf at 573 K at atmospheric
pressure and in a flow of dry nitrogen.
14 Choudary, B. M.; Sateesh, M.; Kantam, M. L.; Prasad, K. V.
R. Appl. Catal. 1998, 171, 155.
15 Choudary, B. M.; Kantam, M. L.; Sateesh, M.; Rao, K. K.;
Santhi, P. L. Appl. Catal. A: Gen. 1997, 149, 257.
16 Bordoloi, A.; Mathew, N. T.; Devassy, B. M.; Mirajkar, S.
P.; Halligudi, S. B. J. Mol. Catal. A: Chem. 2006, 247, 58.
17 Breda, A.; Signoretto, M.; Ghedini, E.; Pinna, F.; Cruciani,
G. Appl. Catal. A: Gen. 2006, 308, 216.
18 Sawant, D. P.; Hartmann, M.; Halligudi, S. B. Microporous
Mesoporous Mater. 2007, 102, 223.
19 Revathi, S.; Esther Leena Preethi, M.; Siddarth, S.; Sivaku-
mar, T. Catal. Commun. 2008, 9, 2043.
Acknowledgements
Support from Islamic Azad University, Shahreza
Branch (IAUSH) Research Council and Center of Ex-
cellence in Chemistry is gratefully acknowledged. R.
Javad Kalbasi also thanks Ms. Elham Tavasoli (Sharif
university of Technology) for her comments.
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FULL PAPER
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