Reactions of dimethyl polysulfides with organomagnesium reagents

Abstract

Reactions of a mixture of dimethyl polysulfides (DMPS, CH3SxCH3, x = 3 – 8) with methyl- and phenylmagnesium halides are described. The type of product obtained was dependent on the molar ratio of DMPS to Grignard reagent. When a 6:1 methyl-Grignard to DMPS ratio was used, methanethiol and dimethyl sulfide were the major products obtained after acidification of the reaction mixture. Lesser quantities of methyl-Grignard favored the formation of dimethyl sulfide, dimethyl disulfide, and H2S. Experiments with a 6:1 phenylmagnesium bromide to DMPS ratio produced benzenethiol and phenylmethyl sulfide as major products after acidification. No methanethiol was observed in these experiments. Mixtures of phenylmethyl mono-, di-, and trisulfides and H2S were obtained with a 3:1 Grignard/DMPS molar ratio. From a mechanistic viewpoint, product distributions obtained from reaction of Grignard reagents with DMPS can be explained by the formation of magnesium thiolates that are most readily stabilized by adjacent structures. Experiments using phenyl Grignard reagent in limited supply suggested that the internal sulfur atoms of the polysulfide chains were most reactive. Keywords: organic polysulfides, Grignard reagents.