Process for mercaptoalkanedicarboxylic acid esters

Claim 1

A process for producing a mercaptoalkane-1,2-dicarboxylic acid alkyl ester having 2 to 3 carbon atoms in the alkane group and 1 to about 24 carbon atoms in the alkyl group comprising the steps of first, forming a reaction mixture comprising hydrogen sulfide, acetic anhydride, and an alkene 1,2-dicarboxylic acid compound selected from the group consisting of alkene 1,2-dicarboxylic acids, alkene-1,2-dicarboxylic anhydrides, alkene-1,2-dicarboxylic esters, alkene-1,2-dicarboxylic amides, and alkene-1,2-dicarboxylic imides; second, heating the reaction mixture at 30° to 230° C. to form an S-acetylthio-1,2-alkanedicarboxylic acid compound in the reaction mixture; third, heating the reaction mixture comprising S-acetylthioalkane-1,2-dicarboxylic acid compound with a selective deacetylating agent to form a mercaptoalkane-1,2-dicarboxylic acid compound in the mixture; fourth, adding as needed alcohol having 1 to about 24 carbon atoms to the reaction mixture and heating to convert to mercaptoalkane-1,2-dicarboxylic acid esters mercaptodicarboxylic acid compounds in the mixture that are not mercaptodicarboxylic esters, and fifth, recovering mercaptoalkane-1,2-dicarboxylic acid ester from the reaction mixture.