Dithiolium salt
File:Dithiolium isomers.pngDithiolium salts are compounds of the formula [(RC)3S2]+X− (R = H, alkyl, aryl, etc.). 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.{{cite book|volume=27 |year=1981|pages=151–239|series=Advances in Heterocyclic Chemistry|title=The 1,2- and 1,3-Dithiolium Ions|author=Noël Lozac'h |author2=Madeleine Stavaux |doi=10.1016/S0065-2725(08)60997-6|isbn=978-0-12-020627-8 }} 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, reactions
1,2-Dithiolium cations have been prepared from 1,3-diketones by treatment with H2S and oxidants such as bromine.{{cite journal|doi=10.1021/jo00954a028|title=Improved Synthesis of Alkyl Substituted 1,2-Dithiolium Salts|author1=Hendrickson, A. R. |author2=Martin, R. L. |journal=Journal of Organic Chemistry|year=1973|volume=38|issue=14 |pages=2548–9}}
:{{Chem2|(RCO)2CH2 + 2 H2S + Br2 -> [(RC)3S2](+)Br(-) + 2 H2O + HBr}}
1,3-Dithiolium cations are often prepared by alkylation of the corresponding unsaturated dithio- or trithiocarbonates:
:{{Chem2|(RC)2S2CE + R'+ -> [(RC)2S2CER']+}}
The analogous reaction of electrophiles with 1,2-dithiole-2-ones affords 1,2-dithiolium cations.