and alkaline media and have low physical strength. In
comparison, clays are cheap, have high physical strength,
and possess relatively high resistance towards alkali treat-
ment. Some work has appeared on the use of clays as
supports for quaternary salts.7-11
Many alkylation reactions are mediated by hydroxyl ions
and conducted under strong alkaline conditions with PTC.
Thus, supporting the phase transfer catalyst on clays would
offer certain advantages, which appear to be distinctly
different due to the fact that clays are inorganic oxide
surfaces with much higher surface areas and bulk densities.
Typically the polymer-supported PTC have bulk densities
that are bracketed between the aqueous and organic phases,
and the mechanistic aspects include this fact. In the case of
clays, the catalyst will be in the continuous phase, and the
type of dispersed phase and the reactant within it would have
a pronounced effect on the yields.
rotovac at 60 °C for 3 h. Since the incipient wetness
technique was used to support the catalyst, followed by
complete drying, all of the catalyst was supported on the
clay. No material was discarded at any time. In addition,
the supported catalyst was weighed to match the material
balance. A quantity equal to 2.743 × 10-3 mol of the
quaternary ammonium salt was used per g of Tonsil.
Experimental Procedure. The reactions were studied in
a 4-cm i.d fully baffled mechanically agitated contactor of
250-mL capacity, which was equipped with a six-bladed
turbine impeller and a reflux condenser. The reactor was
It was preferred to study the synthesis of benzoic
anhydride, a reaction of commercial significance,12 to
compare the use of a clay-supported PTC with that of a
polymer. The modelling aspects were also considered to be
important. Benzoic anhydride is an important intermediate,
which is used as a component in bleaching formulations and
as an ingredient in soldering flux. It is used as a benzoylating
agent in special situations where benzoyl chloride is unsat-
isfactory because of its excessive reactivity or the generation
of hydrochloric acid. There is no report on the use of L-L-S
PTC in the preparation of benzoic anhydride either with
polymer or clay supports. This paper delineates our studies
on the synthesis of benzoic anhydride from benzoic acid and
benzoyl chloride with Tonsil clay-supported catalyst.
immersed in a thermostatic bath whose temperature could
be maintained within 0.5 °C of the desired temperature.
Typical experiments were conducted by taking 0.025 mol
of benzoyl chloride in chloroform (25 mL), 0.04 mol of
benzoic acid and 0.04 mol of sodium hydroxide in water
(20 mL), and a suitable quantity of clay-supported PTC
maintained at 30 °C by using a thermostatic bath. Benzoic
anhydride was the only product formed in the reaction
mixture.
Method of Analysis. Samples of the organic phase were
withdrawn at particular intervals of time, and benzoic
anhydride and benzoyl chloride were analysed by means of
gas-liquid chromatography on Chemito 8510 model. Quan-
titative results were obtained by comparison with synthetic
standards. A 2.0 m × 3.2 mm i.d. stainless steel column
packed with Chromosorb WHP, which was impregnated with
10% SE-30, was used for analysis.
Experimental Section
Chemicals. Benzoyl chloride, sodium hydroxide, benzoic
acid, methanol, and chloroform of LR grade were obtained
from M/s s.d. Fine Chemicals Pvt. Ltd, Mumbai, India.
Cetyltrimethylammonium bromide (CTAB) was procured
from M/s s.d. Fine Chemicals Ltd. and Tonsil clay from
Sudchemie AG, Munchen, Germany. A commercial polymer-
supported catalyst FF-IP was procured from M/s Ion
Exchange (India) Ltd., Mumbai, India.
Catalyst Preparation. A known quantity of Tonsil clay
was vaccum dried for 5 h at 80 °C. It was then transferred
to a three-necked flask with a magnetic stirrer, and vacuum
was applied to the system. From another neck cetyltrim-
ethylammonium bromide (CTAB) dissolved in methanol was
added dropwise from the vacuum tight addition funnel. Since
the porosity of the clay was known, the quantity of methanol
taken was equal to the pore volume. The amount of CTAB
supported on the clay was equal to that used for the L-L
PTC experiment. Typically it was 1 g of CTAB per 1 g of
clay. Stirring was continued under vacuum until all of the
methanol had evaporated. Then it was dried completely in a
Results and Discussion
All experiments were done with CTAB supported on
Tonsil clay as the catalyst unless mentioned otherwise.
Mechanism of Clay-Supported PTC. The mechanisms
of L-L-S PTC have been evaluated in our laboratory,13
depending on whether the support is wetted by the aqueous
phase or organic phase or is of mixed-wet type, which is
decided by the contact angle. Under a dynamic situation, a
strongly water-wet system always retains a thin film of water
around the particle. The organic phase, even though continu-
ous, does not penetrate inside the pores of the catalyst. Thus,
the catalytic action is limited to the exterior surface of the
support. In the case of clay-supported catalyst, the mechanism
needs to be properly understood. The clay-particles were
coated with the quaternary salt. The organic phase was the
continuous phase, and the aqueous phase the dispersed phase.
The wettability of the clay containing quaternary salt as a
solid occupying the pores is water-wet. Typically the aqueous
phase droplet, upon intense agitation, would stick to the clay-
(7) Monsef-Mirzai, P.; McWhinnie, W. R. Inorg. Chim. Acta 1981, 52, 211.
(8) Tundo, P.; Venturello, P.; Angelletti, E. J. Am. Chem. Soc. 1982, 104, 6547.
(9) Tundo, P.; Venturello P.; Angelletti E. J. Am. Chem. Soc. 1982, 104, 6551.
(10) Choudary, B. M.; Rao, S.; Prasad, B. P. Clays Clay Miner. 1991, 39, 3,
329.
(13) (a) Yadav, G. D.; Naik S. S. Unpublished work, 1999. (b) Naik, S. S. Insights
in Catalysis: NoVelties of Multi-Phase transfer catalysis. Ph.D. Thesis,
University of Mumbai, April 1998.
(11) Li, L. C.; Pinnavaia, T. J. Chem. Mater. 1991, 3, 213.
(12) Yeadon, A.; Turney, T. A.; Ramsay, G. J. Chem Educ. 1985, 62(6), 518.
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Vol. 4, No. 3, 2000 / Organic Process Research & Development