Benzene-1,2-dithiol

Benzene-1,2-dithiol is the organosulfur compound with the formula C$6$H$4$(SH)$2$. This colourless viscous liquid consists of a benzene ring with a pair of adjacent thiol groups. The conjugate base of this diprotic compound serves as chelating agent in coordination chemistry and a building block for the synthesis of other organosulfur compounds.

Synthesis
The compound is prepared by ortho-lithiation of benzenethiol using butyl lithium (BuLi) followed by sulfidation:
 * C$6$H$5$SH + 2 BuLi → C$6$H$4$SLi-2-Li + 2 BuH
 * C$6$H$4$SLi-2-Li + S → C$6$H$4$(SLi)$2$
 * C$6$H$4$(SLi)$2$ + 2 HCl → C$6$H$4$(SH)$2$ + 2 LiCl

The compound was first prepared from 2-aminobenzenethiol via diazotization. Alternatively, it forms from 1,2-dibromobenzene.

Reactions
Oxidation mainly affords the polymeric disulfide. Reaction with metal dihalides and metal oxides gives the dithiolate complexes of the formula L$n$M(S$2$C$6$H$4$) where L$n$M represents a variety of metal centers, e.g. (C$5$H$5$)$2$Ti. Ketones and aldehydes condense to give the heterocycles called dithianes:
 * C$6$H$4$(SH)$2$ + RR’CO → C$6$H$4$(S)$2$CRR’ + H$2$O

Related compounds
3,4-Toluenedithiol, also called dimercaptotoluene (CAS#496-74-2), behaves similarly to 1,2-benzenedithiol but is a solid at ambient temperatures (m.p. 135-137 °C).

Alkene-1,2-dithiols are unstable, although metal complexes of alkene-1,2-dithiolates, called dithiolene complexes, are well known.