The chloromethyl sulfide of methyl 8-mercaptopropionate has been prepared. A phthalimide derivative of this ester has been made and hydrolyzed to the phthalimido acid and the (0- carb0xy) benzamido acid. From these products of hydrolysis phthalimidomethyl 8- carboxyethyl sulfone and (o-carboxy) benzamidomethyl 8-carboxyethyl sulfoxide have been prepared. &@'-Dithiodipropionyl chloride and methylene bis (8-thiopropionyl chloride) ...