While most organic sulfides were not oxidized by dimethyl sulfoxide (DMSO), the alkyl 2- chloroethyl sulfides and bis (2-chloroethyl) sulfide slowly reacted with DMSO to produce the corresponding sulfoxides at 25-70 OC under nitrogen. The mechanism of the oxidation is proposed to involve nucleophilic substitution by DMSO followed by neighboring sulfur participation to form a transient sulfonium ion with a four-membered ring structure. The ...