Room temperature synthesis of diphenylmethane over novel mesoporous Lewis acid catalysts

Highly selective synthesis of diphenylmethane (DPM) was carried out by Friedal–Crafts benzylation of benzene using benzyl chloride (BC) as alkylating agent in the presence of a flow of nitrogen under liquid phase reaction conditions over novel mesoporous SO42−/Al-MCM-41 catalysts with different Si/Al ratios. For these reactions, the influences of various reaction parameters, such as different catalysts, reaction temperature, time, mmol ratios of reactants and recyclability are discussed. With increasing the Si/Al ratios of SO42−/Al-MCM-41 catalysts from 21 to 83, the conversion of BC and selectivity of DPM decreased because the number of Lewis acid sites in SO42−/Al-MCM-41 catalysts are found to decrease almost linearly with increasing ratios of Si/Al. Further the catalytic results were compared with those obtained by using 0.8N sulfuric acid, different Si/Al ratios of Al-MCM-41, HY, Hβ, HM and H-ZSM-5 zeolites. From the comparison of the results, SO42−/Al-MCM-41(21) is found to be a highly active and recyclable heterogeneous catalyst for the highly selective synthesis of DPM. Thus, the selectivity of DPM in SO42−/Al-MCM-41(21) is higher than that in other SO42−/Al-MCM-41 (Si/Al = 42 and 83), Al-MCM-41 (Si/Al = 21, 42 and 83), HY, Hβ, HM and H-ZSM-5.

Graphical abstractThe mesoporous molecular sieves Al-MCM-41 and SO42−/Al-MCM-41 with different Si/Al = 21, 42 and 83 were synthesized under hydrothermal and impregnation conditions, respectively, using cetyltrimethylammonium bromide surfactants as template in the absence of auxiliary organics. The mesoporous materials were characterized using several sophisticated instrumental techniques [M. Selvaraj, P.K. Sinha, K.S. Seshadri, A. Pandurangan, Appl. Catal. A: Gen., 265 (2004) 75]. The materials have been used as catalyst for synthesis of diphenylmethane (DPM) using benzene and benzyl chloride (BC) in various optimal conditions. Further the catalytic results were compared with those obtained by using 0.8N sulfuric acid, different Si/Al ratios of Al-MCM-41, HY, Hβ, HM and H-ZSM-5 zeolites. The recyclable SO42−/Al-MCM-41(21) catalyst exclusively forms the product DPM and has much higher yields than other solid acid catalysts. .Figure optionsDownload full-size imageDownload as PowerPoint slide