Divergent decomposition pathways of DMSO mediated by solvents and additives

DMSO (dimethyl sulfoxide) plays an increasingly significant role in various synthetic processes by generating diverse active intermediates in situ, which actively participate in reactions. It is crucial to control the formation of these active intermediates to prevent their mutual interference during utilization. Our previous research identified methyl methanethiosulfonate (MMTS) as a major decomposition product of DMSO when catalyzed by small amounts of (COCl)₂ in CH₃CN. In the current study, we investigated how different solvents and additives can mediate the formation of MMTS. Complete avoidance of MMTS formation was achieved in 1,4-dioxane, while only trace amounts were observed in toluene, MTHF, or CHCl₃. Moreover, the decomposition pathway of DMSO in these solvents was effectively mediated through the addition of strong acids (HX, where X = TfO, ClO₄, I, Br, or Cl) or in the presence of LiI, CH₃I, or Br₂. The effects of solvents and additives on the decomposition of DMSO were explored. The possible mechanisms for the decomposition of DMSO under different conditions were proposed and discussed.