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2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
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CHOUDHARY AND JANA
[
1]
methodfor the preparation of aromatic ketones.
AlCl as a homogeneous catalyst in the acylation, however, poses several
The use of anhydrous
3
serious problems, such as requirement of the catalyst in more than stoichio-
metric amounts, difficulty in the separation and recovery of the catalyst,
disposal of the spent catalyst, corrosion problems, etc. Moreover, this
catalyst is highly moisture sensitive and hence demands moisture-free reac-
tants andsolvent andalso dr y atmosphere for its han dl ing. Because of its
higher moisture sensitivity, the results obtainedwith this catalyst are seldom
reproducible. Hence development of easily separable solid catalysts having
high activity but little or no moisture sensitivity for the acylation reactions
is, therefore, of great practical importance. A number of solidacidcatalysts,
[
2–4]
[5]
such as Hb, HY andH-ZSM-5 zeolites,
heteropoly acids, modified
[6]
ZrO2 have been reportedearlier for the acylation reactions. However,
these catalysts have poor activity for the acylation.
[7]
Our earlier studies reveal that Ga O (or In O )/Si-MCM-41 has
2
2
3
3
very high activity with little or no moisture sensitivity in the benzylation
of benzene. We report here the synthesis of different aromatic ketones in
high yields at a short reaction period (3 h), by the acylation of different
aromatic compounds even in the presence of moisture using Ga O /
2
3
Si-MCM-41, which can be separatedsimply by filtration.
RESULTS AND DISCUSSION
Results showing the influence of solvent, moisture in solvent andload-
ing of Ga O on Si-MCM-41 on the yieldof methoxy benzophenone in the
2
3
ꢀ
benzoylation of anisole by benzoyl chloride (at 80 C) over the Ga O /
2
3
Si-MCM-41 catalyst are presentedin Table 1. The pro du ct yieldfor the
different solvents is in the following order: n-heptane<acetonitrile<dichlor-
oethane. As expected, the yield is also increased with increasing the Ga O
2
3
loading. It is interesting to note that, the presence of moisture in the solvent
has a beneficial effect on the product yield; it has caused a significant increase
in the product yield.
The results showing the product yields in the acylation of different
ꢀ
aromatic compounds with different acyl chlorides (at 80 C) over the
Ga O (20%)/Si-MCM-41 catalyst in the presence or absence of moisture
2
3
in the reaction mixture are presentedin Table 2. From the results, following
important observations can be made:
–
In all the cases, the product yield is quite high, indicating high
acylation activity of the catalyst.