HOOCCH2SH

HOOCCH2SH, commonly known as thioglycolic acid or 2-mercaptoacetic acid, is an organosulfur compound consisting of a carboxyl group and a thiol group on adjacent carbon atoms. Its molecular formula is C2H4O2S, and its molecular weight is approximately 92.12 g/mol. The molecule is a small, colorless liquid with a characteristic strong, thiol-like odor. It is miscible with water and many common organic solvents. The carboxyl group provides acidic character (pKa around 2.6 for the carboxyl), while the thiol group has a higher pKa near 10, allowing deprotonation under basic conditions.

Thioglycolic acid is used as a reducing agent in various chemical and cosmetic applications, most notably in hair care products for permanent waving and hair straightening, where it reduces disulfide bonds in keratin. It also serves as a versatile intermediate in organic synthesis, where it is converted to thiolate esters and other sulfur-containing compounds. In addition, it forms thioglycolate salts that act as chelating or stabilizing agents in different formulations and industrial processes.

Chemically, the compound can undergo oxidation to form disulfides, giving a dimeric product in which two mercaptoacetyl units are linked by a disulfide bond (R-S-S-R). It can react with alcohols to form thioesters and with various electrophiles at the carboxyl group, enabling a range of synthetic transformations.

Safety considerations include potential irritation to skin, eyes, and the respiratory tract, and odor detection can be strong. It should be handled with appropriate personal protective equipment in a well-ventilated area, keeping it away from oxidizers and incompatibles.