Synthesis of diphenylmethane derivatives in Lewis acidic ionic liquids

Diphenylmethane and its derivatives were prepared via Friedel-Crafts benzylation reaction using ionic liquids of 1-butyl-3-methylimidazolium chloride-ZnCl2 (BmimCl-ZnCl2), 1-butyl-3-methylimidazolium chloride-FeCl3 (BmimCl-FeCl3) and 1-butyl-3-methylimidazolium chloride-FeCl2 (MmimCl-FeCl2) as both reaction media and Lewis acid catalysts. In comparison with the reaction performed in conventional organic solvent, faster reaction rate and higher selectivity to target products were achieved in such ionic liquids media. The effects of reaction temperature, reaction time, and the ratio of metal chloride to BmimCl, as well as the amount of ionic liquids on the Friedel-Crafts benzylation were also investigated. It was found that increasing reaction temperature led to high catalytic activity and selectivity, and that the excess amount of Lewis acidity of ionic liquid was detrimental to the reaction. Moreover, these ionic liquids could be conveniently recovered for recycled use; in particular, BmimCl-ZnCl, with moisture-stability could be reused at least eight times without loss of catalytic activity. (c) 2005 Elsevier B.V. All rights reserved.