Benzylation of benzene, toluene and anisole with benzyl alcohol catalyzed by cation-exchange resins

Abstract

The catalytic activity of gel and macroreticular ion-exchange resins (Lewatit and Amberlyst-15) was evaluated for the reaction of benzene with benzyl alcohol and benzyl chloride at 80°C in the liquid phase. With benzyl chloride, the monobenzylation product, diphenylmethane, was obtained in low yield, both with the gel and the macroreticular resins. Better results were obtained with benzyl alcohol as benzylation agent and the most active resin was Amberlyst-15. The benzylation of toluene and anisole with benzyl alcohol, catalyzed by Amberlyst-15, was also evaluated, the conversion of benzyl alcohol being proportional to the concentration of acid sites in the resin. Monobenzylation to benzyl toluene or benzyl anisole is the main reaction and the selectivity was usually found to be higher than 80%, when a toluene/alcohol or anisole/alcohol molar ratio of 10 is used. Secondary reactions to dibenzyl toluenes, dibenzyl anisole and benzyl ether occur to a varying extent, depending on the substrate ratios. In all cases, predominance of ortho/para isomers was observed.