Acylation of aromatic compounds using moisture insensitive InCl3 impregnated mesoporous Si-MCM-41 catalyst

Article abstract of DOI:10.1016/S0040-4039(01)02335-8

Acylation of aromatic compounds (benzene, toluene, p-xylene, mesitylene, anisole, naphthalene, methylnaphthalene and methoxynaphthalene) by an acyl chloride (benzoyl chloride, phenylacetyl chloride, propionyl chloride or butyryl chloride) in high yield, in a short reaction period (3 h), even in the presence of moisture in the aromatic substrate or solvent (dichloroethane), can be accomplished at low temperature (80±1°C) using an InCl₃ impregnated Si-MCM-41 catalyst in low catalyst concentration.

Full text of DOI:10.1016/S0040-4039(01)02335-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 1105–1107
Acylation of aromatic compounds using moisture insensitive
InCl3 impregnated mesoporous Si-MCM-41 catalyst
Vasant R. Choudhary,* Suman K. Jana and Nilesh S. Patil
Chemical Engineering Division, National Chemical Laboratory, Pune 411 008, India
Received 10 October 2001; revised 16 November 2001; accepted 6 December 2001
Abstract—Acylation of aromatic compounds (benzene, toluene, p-xylene, mesitylene, anisole, naphthalene, methylnaphthalene
and methoxynaphthalene) by an acyl chloride (benzoyl chloride, phenylacetyl chloride, propionyl chloride or butyryl chloride) in
high yield, in a short reaction period (3 h), even in the presence of moisture in the aromatic substrate or solvent (dichloroethane),
can be accomplished at low temperature (80 1°C) using an InCl3 impregnated Si-MCM-41 catalyst in low catalyst concentration.
© 2002 Elsevier Science Ltd. All rights reserved.
Aromatic ketones are important fine chemicals and/or
intermediates for the preparation of fine chemicals in
the dyestuffs, pharmaceutical and other chemical indus-
tries. The conventional method for the preparation of
aromatic ketones is based on the homogeneous Friedel–
Crafts acylation of aromatic hydrocarbons with acid
chlorides using more than stoichiometric amounts of
anhydrous AlCl3 as catalyst.1 However, the use of
anhydrous AlCl3 as a catalyst poses several problems,
such as difficulty in its separation and recovery, dis-
posal of spent catalyst, corrosion problems, etc. More-
over, this catalyst is highly moisture sensitive and hence
demands moisture-free reactants and solvents and also
must be handled under a dry atmosphere. Because of its
very high moisture sensitivity, the results obtained with
this catalyst are seldom reproducible. Hence the devel-
opment of easily separable solid catalysts having high
activity but little or low moisture sensitivity in the
acylation reactions is, therefore, of great practical
importance. In earlier studies, a number of solid acid
catalysts, such as Hb, HY, H-ZSM-5 zeolites,2–4 hetero-
activity.7,8 Hence, it is interesting to study the acylation
of aromatic compounds using the InCl3/Si-MCM-41
catalyst. We report here that, the InCl3 impregnated
mesoporous Si-MCM-41 catalyst shows high activity in
the acylation of different aromatic compounds by acyl
chlorides and, also, that this catalyst does not demand
moisture-free reaction conditions for the acylation
reaction.
Results showing the product yields in the acylation of
different aromatic compounds with acyl chlorides (viz.
benzoyl chloride, phenylacetyl chloride, propionyl chlo-
ride and butyryl chloride) (at 80 1°C)9 using the InCl3/
Si-MCM-41 catalyst (loading of InCl3=20 wt%),10
using dichloroethane (DCE), acetonitrile (ACN) or n-
heptane as a solvent, in the presence or absence of
moisture in the reaction mixture, are presented in Table
1.
The product yield in all the cases is quite high, indicat-
ing the high acylation activity of the catalyst, even in
the presence of moisture in the aromatic substrate
and/or solvent. In the cases of the substituted benzenes
and naphthalenes, acylation at the ortho position rela-
tive to that of the para position was found to be very
small, indicating a high regioselectivity in the acylation.
The presence of moisture has a beneficial effect leading
to an increase in the product yield. A similar beneficial
effect of moisture was observed in the acylation of
toluene using the In2O3/Si-MCM-41 catalyst.7
poly acids5 and modified ZrO2 have been reported for
6
acylation reactions. However, these solid acid catalysts
show poor activity for the acylation. In contrast, In2O3/
Si-MCM-41, which is basic in nature, shows very good
acylation activity.7 Our earlier studies indicated that, in
comparison to In2O3/Si-MCM-41, the InCl3/Si-MCM-
41 catalyst shows much higher benzene benzylation
Keywords: acylation of aromatic compounds; InCl3 impregnated
mesoporous Si-MCM-41 catalyst.
* Corresponding author. Tel.: (+91) 20-5893041; fax: (+91) 20-
5893041/5893355; e-mail: vrc@ems.ncl.res.in
Among the three solvents used for the acylation of
anisole, n-heptane is the least preferred and ACN and
DCE showed comparable performance. For the
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)02335-8

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V. R. Choudhary et al. / Tetrahedron Letters 43 (2002) 1105–1107
Table 1. Results on the acylation reactions of different aromatic compounds using the InCl3/Si-MCM-41 catalyst (reaction
mixture: 20.0 mmol of moisture-free aromatic compound+11.0 ml of moisture-free solvent+8.6 mmol of acyl chloride,
amount of catalyst=0.4 g, temperature=8091°C, reaction period=3 h
Entry
Substrate
Acylating agent
Solvent
Main productc
Yield (%)
1
2
3
4
5
6
7
8
Anisole
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C6H5COCl
C2H5COCl
C2H5COCl
C3H7COCl
C6H5CH2COCl
DCE
DCE
DCEb
DCEb
ACN
n-Heptane
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
4-Methoxybenzophenone
4-Methoxybenzophenone
4-Methoxybenzophenone
4-Methoxybenzophenone
4-Methoxybenzophenone
4-Methoxybenzophenone
Benzophenone
Benzophenone
4-Methylbenzophenone
4-Methylbenzophenone
2,5-Dimethylbenzophenone
2,4,6-Trimethylbenzophenone
1-Benzoylnaphthalene
1-Benzoyl-2-methylnaphthalene
1-Benzoyl-2-methoxynaphthalene
4-Methoxypropiophenone
1-Propio-2-methoxynaphthalene
4-Methoxybutyrophenone
a-(4-Methoxyphenyl) acetophenone
83
84
84
84
82
25
57
57
69
70
74
79
67
74
88
89
92
87
74
Anisolea
Anisole
Anisolea
Anisole
Anisole
Benzene
Benzenea
9
Toluene
10
11
12
13
14
15
16
17
18
19
Toluenea
p-Xylene
Mesitylene
Naphthalene
2-Methylnaphthalene
2-Methoxynaphthalene
Anisole
2-Methoxynaphthalene
Anisole
Anisole
a Aromatic compound saturated with water.
b Solvent saturated with water.
c In the cases of the substituted benzenes and naphthalenes, the yield of ortho acylated product was very small (<8%).
acylation of other aromatic compounds, DCE was used
as the solvent.
RCO++ArH“RCOAr+H+
(4)
[Ar=C6H5, (CH3)C6H4, (CH3)2C6H3, (CH3)3C6H2,
(CH3O)C6H4, C10H7, (CH3)C10H6 or (CH3O)C10H6].
The presence of moisture in the reaction mixture has no
detrimental effect on the acylation activity of the cata-
lyst. This is of great practical importance, as the cata-
lyst does not demand a thoroughly dried aromatic
substrate or solvent nor handling of the catalyst under
moisture-free conditions. The results obtained are quite
reproducible.
The above mechanism is similar to that proposed ear-
lier by Brio et al. for acylation reactions over cation-
exchanged clays.12 This mechanism may, however, be
considered as a speculative one.
In summary, InCl3 impregnated Si-MCM-41 is a highly
active catalyst for the acylation of aromatic compounds
by acyl chlorides even in the presence of moisture in the
reaction mixture.
The benzene benzoylation activity of the InCl3/Si-
MCM-41 catalyst is much higher than that of the
earlier reported In2O3/Si-MCM-41,7 Hb zeolite2 and
clayzic11 catalysts. For these catalysts, the product yield
obtained in the benzene benzoylation and the tempera-
ture and reaction period required were as follows:
In2O3/Si-MCM-41 catalyst 50%, after 5 h at 80°C; Hb
zeolite catalyst 54%, after 18 h at 80°C; and the clayzic
catalyst 66%, after 30 h at 130–140°C.
Acknowledgements
S. K. Jana is grateful to the CSIR, New Delhi for the
award of Research Fellowship.
The moisture insensitivity of the InCl3/Si-MCM-41 cat-
alyst indicates that acylation reactions over this catalyst
are not catalyzed by the Lewis acid sites of the catalyst.
The high acylation activity may be attributed to the
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V. R. Choudhary et al. / Tetrahedron Letters 43 (2002) 1105–1107
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phase and benzene as the eluent. The structures of the
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of InCl3=20 wt%) was prepared by impregnating Si-
MCM-41 (high silica mesoporous MCM-41 with a sur-
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