Selective Alkylation of Methylbenzenes with Cyclohexene Catalyzed by Solid Acids

The synthesis of mixtures of cyclohexyltoluenes from cyclohexene and toluene, catalyzed by solid-acid catalysts, such as zeolites (H-USY, H-BEA, H-Mor) or activated clays (e.g. Filtrol-24), was studied. The ortho/meta/para ratio of these mixtures strongly depends on the structure of the catalysts involved. With zeolite H-USY and Filtrol-24 as the catalysts the meta/para ratio is found to be about 2:1, in agreement with the thermodynamic equilibrium, and the ortho-isomer is absent. As H-USY appeared to be a good isomerization catalyst for the cyclohexyltoluenes, the mechanism might involve ortho/meta/para-alkylation followed by isomerization. In this way a new route has been developed to the expensive intermediate 3-methylbiphenyl. The reaction of cyclohexene with xylenes or mesitylene, catalyzed by the zeolite H-USY or the clay Filtrol-24, gives mixtures of cyclohexylxylenes or cyclohexylmesitylene, respectively.