Process for the preparation of 2-(4-chlorophenylethyl)-2-tert.-butyl-oxirane

A process for making the known fungicide intermediate 2-(4-chlorophenyl ethyl)-2-tert.-butyloxirane of the formula (I) comprising (a) mixing a solution of trimethylsulphonium bromide of the formula (CH3)3S(+)Br(-)(II) in a methanol/toluene mixture with preheated toluene and simultaneously distilling off a methanol/toluene mixture at a temperature between 65 DEG and 110 DEG C. until a suspension having a solids content between 10 and 70% by weight is formed, and (b) reacting the suspension of trimethylsulphonium bromide in toluene thus obtained with 1-(4-chlorophenyl)-4,4-dimethylpentan-3-one of the formula (III) in the presence of solid potassium hydroxide, diethylene glycol and water at a temperature between 20 DEG and 120 DEG C., the amounts of the reaction components being such that per mole of 1-(4-chlorophenyl)-4,4-dimethylpentan-3-one of the formula (III) there are present between 1 and 2 moles of trimethylsulphonium bromide of the formula (II), between 2 and 3 moles of solid potassium hydroxide and also between 0.1 and 10% by weight of diethylene glycol and between 0.5 and 12% by weight of water, relative to 1-(4-chlorophenyl)-4,4-dimethylpentan-3-one of the formula (III).