mercaptan

Mercaptan, commonly used name for thiol compounds, refers to organosulfur species that contain a sulfhydryl group (-SH). In systematic terms, mercaptans are thiols: R-SH, where R denotes an alkyl or aryl group. The name is historic; chemically they are more properly called thiols.

Physically, mercaptans are typically foul-smelling liquids or gases with characteristic odors that help in olfactory detection. The sulfhydryl group imparts acidity (pKa around 10 in water for many aliphatic thiols) and makes them good nucleophiles. They readily oxidize to disulfides (R-S-S-R).

Occurrence and uses: Some mercaptans occur naturally in small amounts; industrially, alkyl mercaptans such as methanethiol and ethanethiol occur in petroleum and are produced commercially for use as odorants for natural gas and LPG; tert-butyl mercaptan is widely used for gas odorization in many countries. They serve as intermediates in the synthesis of pharmaceuticals, agrochemicals, polymers, and rubber vulcanization accelerators.

Synthesis and reactions: Thiols are prepared by various methods, including the thiolation of alkyl halides with thiourea followed by hydrolysis, or by reduction of thioesters or disulfides. They participate in typical thiol chemistry, including nucleophilic substitution, metal complexation, and disulfide formation upon oxidation.

Safety: Mercaptans are flammable and volatile; exposure can irritate the eyes and respiratory tract. Odors may be extremely strong at low concentrations, but sensory fatigue can occur, complicating leak detection. Proper ventilation and handling are required.