Solvents as phase transfer catalysts. Reaction of trimethylsulfonium iodide and solid potassium hydroxide in acetonitrile leading to an epoxide of benzophenone

Abstract

The kinetics of reactions of benzophenone with trimethylsulfonium iodide in acetonitrile in the presence of excess solid potassium hydroxide (KOH) are reported, and the kinetics of formation of products, 2,2-diphenyloxirane, 2,2-diphenylacrylonitrile, and N-(2-hydroxy-2,2-diphenyl)acetamide are also monitored. The effects of water, other cosolvents and quaternary ammonium salts are investigated. Initial rates are lower than rates of comparable reactions involving nitrile formation in the absence of sulfonium salts, and the epoxide reaches a concentration maximum before any nitrile forms. The results can be explained by initial formation of the anion [CH₂CN]^–, which reacts with the sulfonium salt to give Me₂S⁺CH₂^– (ylide, leading to epoxide) before direct reaction of [CH₂CN]^– with benzophenone (leading to nitrile) can occur. Consequently, acetonitrile is acting as a phase transfer catalyst, aiding the transport of base (in a modified form) from the surface of the KOH to form the ylide.