Room temperature synthesis of diphenylmethane over MCM-41 supported AlCl3 and other Lewis acids

Abstract

The catalytic properties of MCM-41 activated with AlCl3, ZnCl2 and other Lewis acids, such as FeCl3, NiCl2 and CuCl2 were investigated for room temperature Friedel-Crafts benzylation in the liquid phase. The catalysts were studied under batch-wise as well as continuous operation conditions. AlCl3/MCM-41 showed higher activity than ZnCl2/MCM-41, while FeCl3/MCM-41, CuCl2/MCM-41 and NiCl2/MCM-41 were inactive under identical conditions. ZnCl2 offered some advantages due to reduced hydrolytic sensitivity and better selectivity. The optimized ZnCl2 loading of ZnCl2/MCM-41 was 4 mmol g-1. For AlCl3/MCM-41, the pore size of MCM-41 did not affect the activity nor the selectivity in the benzylation of benzene. Very low selectivity was observed in the benzylation of substituted aromatics using AlCl3/MCM-41 as catalyst due to a tendency for migration or transfer of the substituent group. With its inherently lower activity, ZnCl2/MCM-41 did not catalyze this reaction. In a continuous trickle bed reactor, sustained activity of the AlCl3/MCM-41 catalyst could be demonstrated. Hence, MCM-41 supported with AlCl3 or ZnCl2 may be promising candidates to replace AlCl3 in the industrial manufacture of diphenylmethanes. © 2001 Elsevier Science B.V.