mercapto

Mercapto is a chemical term used to denote the presence of a thiol group (-SH) in a molecule. In systematic naming, mercapto can function as a prefix (for example, mercaptoethanol) or, when the thiol group is the primary functional group, the suffix -thiol is used. The thiol group is part of organosulfur chemistry and is conceptually related to the hydroxyl group in alcohols, but it is typically more reactive and less acidic.

Common examples include methanethiol (methyl mercaptan, CH3SH) and ethanethiol (ethyl mercaptan, C2H5SH). The IUPAC preferred names are methanethiol and ethanethiol, while common names ending in mercaptan (e.g., methyl mercaptan) refer to the same compounds. Thiols are often volatile and can have strong, characteristic odors, which are especially noticeable for low-molecular-weight species.

Biochemically and industrially important examples include 2-mercaptoethanol (HO–CH2–CH2–SH), used as a reducing agent to break disulfide bonds in proteins, and related compounds such as dithiothreitol (DTT). Thiols participate in a range of reactions, including nucleophilic substitution and formation of thioethers. They can be deprotonated to form thiolate anions and readily oxidize to form disulfides (R–S–S–R), a process central to protein folding and stability.

In industry, mercaptans are also used as odorants to signal the presence of gases; natural gas is commonly odorized with mercaptans to aid leak detection. Overall, mercapto denotes the functional thiol group and its associated chemistry, reactivity, and applications.