Dithiolium salt

Dithiolium salts are compounds of the formula ⁺X⁻. These salts consist of a planar organic cation with a variety of anions such as halides. The five-membered ring cations are observed in either of two isomers, 1,2- and 1,3-dithiolium cations. These cations differ with respect to the relative positions of the pair of sulfur atoms. Both isomers feature a planar ring, which is aromatic owing to the presence of 6π electrons. For example, the 1,2-ditholium ring can be represented as an allyl cation of the three carbons, with each sulfur atom donating one of its lone pairs of electrons to give a total of three pairs.

Preparation, occurrence

1,2-Dithiolium cations have been prepared from 1,3-diketones by treatment with H₂S and oxidants such as bromine.
They also arise by oxidation of 1,2-dithiole-3-thiones with peroxyacetic acid.
1,3-Dithiolium cations are often prepared by alkylation of the corresponding unsaturated dithio- or trithiocarbonates:
The analogous reaction of electrophiles with 1,2-dithiole-2-ones affords 1,2-dithiolium cations.

Reactions

By reduction, 1,2-dithiolium salts are precursors to dithioacetylacetonate complexes:
Primary amines attack 1,2-dithiolium salts to give α,ß-unsaturated β-aminothione derivatives: