Mercaptanen

Mercaptanen, also called mercaptans, are a class of organic sulfur compounds that contain a sulfhydryl group (-SH) bonded to carbon. They are the sulfur analogues of alcohols (R–SH) and share many chemical properties with other thiols. The general formula is R–SH, where R is an organic group. Most mercaptans are colorless liquids or gases with characteristic, strong and often unpleasant odors.

Properties and behavior: Mercaptans have relatively low molecular weights and can be volatile. The -SH bond makes them nucleophilic and reactive toward alkylating agents, leading to thioethers, disulfides (R–S–S–R) upon oxidation, and various metal mercaptide complexes. Their thiol hydrogen is somewhat acidic for hydrocarbons, with pKa values around 10–11, which influences their reactivity and salt formation. They typically have strong odors detectable at very low concentrations, a trait that is exploited in safety applications but also poses odor nuisance in some contexts.

Occurrence and production: Mercaptans occur naturally in many foods and biological processes, such as garlic, onions, and certain cheeses, and can form during fermentation and aging. Industrially, they arise during petroleum refining and natural gas processing, where sulfur-containing compounds are transformed or removed. Synthetically, mercaptans can be prepared by thiolation of organic substrates, reduction of thioesters, or direct substitution reactions involving thiolate species.

Uses and safety: The most important practical use of mercaptans is as odorants for natural gas and LPG, enabling leak detection at very low concentrations. Common odorants include tert-butyl mercaptan and ethyl mercaptan. They are flammable and can irritate the skin, eyes, and respiratory tract; handling requires ventilation and appropriate protective measures. Environmental concerns center on odor nuisance and potential toxicity of certain thiols in higher concentrations.