Friedel-Crafts type benzylation and benzoylation of aromatic compounds over Hβ zeolite modified by oxides or chlorides of gallium and indium

Abstract

Liquid phase benzylation (by benzyl chloride) and benzoylation (by benzoyl chloride) of benzene and other aromatic compounds over different Ga- and In-modified Hβ zeolite catalysts at 80°C have been investigated. An impregnation of the zeolite by oxides or chlorides of Ga and In makes the zeolite highly active in the benzylation process but it results in a decrease in the acidity, particularly the strong acid sites (measured in terms of the ammonia chemisorbed at 250°C) of the zeolite. Both the redox function, created due to the modification of the Hβ zeolite by Ga or In, and the zeolitic acidity seem to play important role in the benzylation or benzoylation process. Among the different Ga- and In-modified Hβ zeolite catalysts, the In₂O₃/Hβ showed highest activity for the benzene benzylation. This catalyst also showed high activity for both the benzylation and benzoylation of other aromatic compounds, even in the presence of moisture in the reaction mixture; in case of the benzoylation, the moisture has beneficial effect. The In₂O₃/Hβ catalyst can be reused in the benzylation for several times. Kinetics of benzene benzylation (using excess of benzene) over the different Ga- and In-modified Hβ zeolite catalysts has also been investigated. A plausible mechanism for the activation of both the reactants (aromatic substrate and benzyl or benzoyl chloride, forming corresponding carbocation) over the catalyst and also for the reaction between the carbocation and the activated and/or non-activated aromatic substrate is proposed.