BENZYLATION OF TOLUENE BY BENZYL-CHLORIDE OVER PROTONIC ZEOLITES

The benzylation of toluene with benzyl chloride was studied at 383 K in the liquid phase on different protonic zeolites: H-ZSM-5, H-BETA and HY. Monobenzylation to benzyltoluenes is the main reaction, usually higher than 90% selectivity when a toluene/benzyl chloride molar ratio of 5 is used. Secondary. reactions to dibenzyl- and tribenzyltoluenes occur to various extent depending on the reaction conditions and catalysts. The most active catalysts, and the most selective to monobenzylation, are those possessing mesopores in the 30-200 angstrom range: H-BETA and dealuminated HY (Si/Al=20). On these zeolites it is proposed that intracrystalline catalysis occurs, shape selectivity then preventing secondary reactions. At variance, on the other zeolites, H-ZSM-5 and nondealuminated HY, the reaction takes place at the external surface of the grain yielding a lower activity and selectivity to monobenzylation.