Alkaline Decomposition of Triarylsulfonium Halides with Various Bases

Abstract

Abstract Alkaline decomposition of triarylsulfonium bromides with various bases was found to give different products depending on the nature of the bases. The reaction of triarylsulfonium bromide with either piperidide anion or thiophenoxide ion seems to proceed with the initial attack of piperidide anion or thiophenoxide ion of the carbon atom of C-S bond (SN reaction on carbon atom), while the reaction of diarylethoxysulfonium tetrafluoroborate with thiophenoxide ion is presumed to involve the initial attack of thiophenoxide ion on the sulfur atom at low temperature (SN reaction on sulfur atom). When triarylsulfonium bromide was subjected to the reaction with potassium hydroxide in aqueous ethanol, the main path was the alkaline decomposition which proceeds via the nucleophilic attack of the ethoxide ion on the sulfur atom. In the treatment with hydroxide ion in water, the decomposition appears to proceed mainly via two mechanistic routes, i.e., the processes involving the nucleophilic attack of hydroxide ion on both aromatic carbon and the sulfur atoms. A free radical process cannot be excluded, but appears unlikely.