Efficient use of trimethylsulfonium methylsulfate as a reagent for the epoxidation of carbonyl-containing compounds

A process for the efficient conversion of trimethylsulfonium methylsulfate into dimethylsulfonium methanide, thence epoxides, has been devised. Thus dimethyl sulfate and dimethyl sulfate are caused to react in the presence of either a mineral acid or an organic acid. The anion of trimethylsulfonium methyl sulfate is converted by the acid into methyl hydrogen sulfate, which in turn reacts with excess dimethyl sulfide to form trimethylsulfonium hydrogen sulfate. The outcome is that both methyl groups of dimethyl sulfate are converted into the desired trimethylsulfonium salt, thence dimethylsulfonium methanide; the process is mediated by low boiling dimethyl sulfide which can be recycled, and the by-product (K₂SO₄) is more easily disposed of than potassium methyl sulfate. © The Royal Society of Chemistry 1999.