1995 Volume 21 Issue 6 Pages 1147-1153
Insoluble heteropoly acid catalysts were prepared from H3PW12O40 by partial ion exchange with various alkaline ions. The Friedel-Crafts acylation of toluene with benzoic anhydride in the liquid phase (batch mode, 383K) was carried out in order to apply the strong acidity of these catalysts.
H0.5Cs2.5PW12O40obtained by partial ion exchange with cesium ion followed by calcination at 573K showed acid strength higher than pKa=-8.2 and exhibited the highest catalytic activity. The reaction was not completed and the final yield of phenyl tolyl ketone (PTK) was about 60% but the activity was comparable to a typical solid super acid catalyst (H2SO4/ZrO2).
Repeated use of the catalyst showed that incomplete conversion was not caused by irreversible deactivation. Reversible depression of the acylation was explained by; the loss of benzoic anhydride by the reaction of activated benzoic anhydride. with the ketone (PTK) produced, the strong adsorption of the ketone (PTK) produced and of water in the system. The reaction paths were discussed on the basis of the identification of side products. A rate equation was also proposed.