Method for preparing mercapto propionic acid esters and polythio dipropionic acid esters

A process for the preparation of at least one reaction product selected from the group consisting of mercaptopropionic acid esters of the formula:

• HS -- CH.sub.2 -- CH.sub.2 -- COOR
• and polythiodipropionic acid esters of the formula:
• ##STR13## wherein n is a number from 2 to 10 and R is selected from the group consisting of alkyl, cycloalkyl, and alkyl cycloalkyl having from one to about eight carbon atoms which comprises reacting hydrogen sulfide and an acrylic acid ester of the formula:
• CH.sub.2 .dbd.CH -- COOR
• wherein R is selected from the group consisting of alkyl, cycloalkyl, and alkyl cycloalkyl having from one to about eight carbons atoms, and elemental sulfur in an amount within the range from about 0.01 to about 5 moles per mole of acrylic acid ester in an essentially nonaqueous system containing less than 5% water and in the presence of a reactive solvent comprising polythiodipropionic acid ester of the formula above;
• the polythiodipropionic acid ester being present in an amount of at least 30% by weight of the total of any monothiodipropionic acid ester and of the polythiodipropionic acid ester present;
• a weakly basic amine catalyst selected from the group consisting of ammonia, primary, secondary, and tertiary amines and quaternary amines;
• the weakly basic amine catalyst being present in an amount within the range from about 0.1 to about 10% by weight of the reaction mixture;
• the reaction being carried out at a temperature within the range from about 0 to about 150.degree. C and an H.sub.2 S concentration within the range from about 0.1% to saturation in the reactive solvent under the reaction conditions;
• and recovering at least one reaction product selected from the group consisting of mercaptopropionic acid ester and polythiodipropionic acid ester from the resulting reaction mixture.