Thioldisulfide

Thioldisulfide is a nonstandard term used in sulfur chemistry to refer to compounds that contain an S–S bond in which the attached groups are sulfur-containing moieties. In most contexts these species are simply called disulfides, with the general structure R–S–S–R' (and the hydrogen analog H–S–S–H). The qualifier “thio-” in older literature may be used to emphasize sulfur-rich substituents, but the term thioldisulfide is ambiguous and not part of formal IUPAC nomenclature.

Structure and occurrence: The core motif is an S–S single bond; substituents can be thiol-derived groups, and the attached fragments can be alkyl, aryl, or biomolecular pieces. The simple inorganic hydrogen disulfide, H2S2, is the two-sulfur hydride related to this class.

Preparation and reactions: Disulfides are commonly formed by the oxidation of thiols: 2 R–SH + [O] → R–S–S–R' + H2O. They can also arise by radical coupling or thiol–disulfide exchange processes. The S–S bond is cleaved reductively to regenerate thiols, and mixed disulfides (RSSR'') form via exchange with other thiols.

Properties and applications: Low-molecular-weight disulfides are typically colorless liquids or gases with characteristic sulfur odors. In biology, disulfide bonds stabilize protein structure and participate in redox signaling. In organic synthesis, disulfides serve as crosslinkers and intermediates in thiol-based chemistry. Safety considerations reflect the sulfur nature of these compounds: many are odorous and can be irritating; appropriate containment and handling are advised.

See also: disulfide, thiol, thioether; hydrogen disulfide.