Chloromethyl methyl sulfide is the organosulfur compound with the formula . In terms of functional groups, it is a thioether and an alkyl chloride. The compound is structurally related to sulfur mustards, i.e., it is a potentially hazardous alkylating agent. The compound finds some use in organic chemistry as a protecting group. In the presence of base, it converts carboxylic acids (RCO2H) to esters .[1] The compound is prepared by treatment of dimethylsulfide with sulfuryl chloride.[2]