Study on Autocatalytic Decomposition of Dimethyl Sulfoxide (DMSO) II: Analysis of Intermediate Substances Obtained in the Induction Period and Investigations Regarding Formic Acid

Dimethyl sulfoxide (DMSO) is a good solvent as well as a mild oxidizing agent. Several severe incidents associated with DMSO decomposition have been reported in spite of its wide use. The goal of this study is to understand the early stage of DMSO decomposition. In repeated isothermal heating tests of DMSO in an inert atmosphere, two kinds of intermediate substances were found: one contained labile, turbid compounds in the liquid phase, and the other was a white material deposited on the inner wall of the headspace. Analyses of these intermediates were carried out. Among the acids formed in the isothermal heating, formic acid (FA) had the maximum concentration and exhibited the largest effect on shortening the induction period. The behavior and effect of FA on DMSO decomposition were investigated, and it was demonstrated that FA created an equimolar adduct with DMSO. It was also found that a small addition of FA greatly influenced the DMSO decomposition pathways.