Thiotiols

Thiotiols, commonly called thiols or mercaptans, are organic compounds that contain the sulfhydryl group, -SH, bonded to carbon. The general formula is R-SH, where R is an alkyl or aryl group. The systematic IUPAC name is an alkanethiol or arenethiol; examples include methanethiol (CH3SH), ethanethiol (C2H5SH), and benzenethiol (thiophenol, C6H5SH).

Nomenclature and classification

Thiols are classified as aliphatic or aromatic based on the carbon framework attached to the -SH group. They are often distinguished from sulfides (R-S-R′) and disulfides (R-S-S-R) by the presence of the acidic -SH proton.

Properties

Thiols are generally more acidic than alcohols, with pKa values around 10–11 for many aliphatic thiols, due to the stabilizing sulfur atom. They form thiolate anions (RS−) upon deprotonation, which are good nucleophiles and react readily in substitution and addition reactions. Thiols readily oxidize to disulfides (R-S-S-R) in air or with oxidants. They typically have strong, characteristic odors and can be malodorous or toxic; they are also generally flammable.

Preparation and reactions

Common laboratory methods to prepare thiols include nucleophilic substitution of alkyl halides with sodium hydrosulfide (R-X + NaSH → R-SH) or the hydrolysis of thiourea derivatives derived from alkyl halides. Reactions of thiols include deprotonation to RS−, alkylation to form thioethers (R-S-R′), and oxidation to disulfides. They can act as ligands, binding to metals through sulfur, and play roles in organic synthesis and polymer chemistry.

Occurrence and applications

In biology, thiols are structural or catalytic components of many molecules, notably the amino acid cysteine and the tripeptide glutathione. In industry, thiols provide the characteristic odor to natural gas for leak detection (mercaptan odorants) and feature in various organic syntheses and materials.

Safety

Thiols can be irritating and toxic in concentrated forms; they are highly reactive and often volatile, requiring appropriate handling and ventilation.