Sulfen

Sulfen is a term that appears in chemical literature but is not an officially recognized element or a standard functional-group name in contemporary nomenclature. It is most often encountered as an informal or historical label for sulfur-centered fragments in organic chemistry rather than a defined class of compounds.

Modern conventions prefer sulfenyl (or sulfanyl) to designate a sulfur atom bonded to a substituent, written as R-S-. The neutral sulfur-centered radical R-S• is usually called a thiyl or sulfanyl radical. In practice, sulfenyl is the preferred descriptor for the sulfur-containing fragment in synthetic sequences, while sulfen is rarely used in current IUPAC nomenclature.

Common sulfenyl-containing compounds include sulfenyl chlorides (R-S-Cl), sulfenyl sulfides (R-S-S-R), and related derivatives. These species are typically prepared from thiols by chlorinating agents such as thionyl chloride or oxalyl chloride, giving R-S-Cl that can undergo further substitution to form thioethers or sulfenamides. In biological and chemical contexts, oxidation of thiols can yield sulfenyl intermediates, such as sulfenic acids (R-S-OH), which are distinct from the neutral sulfenyl fragments.

Because of its ambiguous usage, the term sulfen should be avoided in formal writing in favor of sulfenyl or thiyl terminology to ensure precision.