Room temperature synthesis of diphenylmethane over MCM-41 supported AlCl 3 and other Lewis acids

Abstract

The catalytic properties of MCM-41 activated with AlCl 3, ZnCl 2 and other Lewis acids, such as FeCl 3, NiCl 2 and CuCl 2 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. AlCl 3/MCM-41 showed higher activity than ZnCl 2/MCM-41, while FeCl 3/MCM-41, CuCl 2/MCM-41 and NiCl 2/MCM-41 were inactive under identical conditions. ZnCl 2 offered some advantages due to reduced hydrolytic sensitivity and better selectivity. The optimized ZnCl 2 loading of ZnCl 2/MCM-41 was 4 mmol g −1. For AlCl 3/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 AlCl 3/MCM-41 as catalyst due to a tendency for migration or transfer of the substituent group. With its inherently lower activity, ZnCl 2/MCM-41 did not catalyze this reaction. In a continuous trickle bed reactor, sustained activity of the AlCl 3/MCM-41 catalyst could be demonstrated. Hence, MCM-41 supported with AlCl 3 or ZnCl 2 may be promising candidates to replace AlCl 3 in the industrial manufacture of diphenylmethanes.