Dithiolium salt

Dithiolium 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.^[1] For example, the 1,2-ditholium ring can be represented as an allyl cation of the three carbons,^[2] with each sulfur atom donating one of its lone pairs of electrons to give a total of three pairs.

Structure of diphenyl-1,2-dithiolium cation (as its bisulfate salt). Selected distances: S-S = 2.019(5); S-C=173(1); C_ring-C_ring = 1.38(1) Å.^[3]

Preparation, occurrence, reactions

1,2-Dithiolium cations have been prepared from 1,3-diketones by treatment with H₂S and oxidants such as bromine.^[2]

(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:

(RC)₂S₂CE + R'⁺ → [(RC)₂S₂CER']⁺

The analogous reaction of electrophiles with 1,2-dithiole-2-ones affords 1,2-dithiolium cations.

References

^ Noël Lozac'h; Madeleine Stavaux (1981). The 1,2- and 1,3-Dithiolium Ions. Advances in Heterocyclic Chemistry. Vol. 27. pp. 151–239. doi:10.1016/S0065-2725(08)60997-6. ISBN 978-0-12-020627-8.
^ ^a ^b Hendrickson, A. R.; Martin, R. L. (1973). "Improved Synthesis of Alkyl Substituted 1,2-Dithiolium Salts". Journal of Organic Chemistry. 38 (14): 2548–9. doi:10.1021/jo00954a028.
^ E. Uhlemann; F. Weller (1992). "3,5-Diphenyl-1,2-dithiolium-hydrogensulfat—Bildung und Struktur" [3.5-Diphenyl-l,2-dithiolium Hydrogensulphate—Synthesis and Structure]. Z. Naturforsch. B (in German). 47 (11): 1501–1504. doi:10.1515/znb-1992-1102. S2CID 95736614.

[1] Noël Lozac'h; Madeleine Stavaux (1981). The 1,2- and 1,3-Dithiolium Ions. Advances in Heterocyclic Chemistry. Vol. 27. pp. 151–239. doi:10.1016/S0065-2725(08)60997-6. ISBN 978-0-12-020627-8.

[Hendrickson1973-2] Hendrickson, A. R.; Martin, R. L. (1973). "Improved Synthesis of Alkyl Substituted 1,2-Dithiolium Salts". Journal of Organic Chemistry. 38 (14): 2548–9. doi:10.1021/jo00954a028.

[3] E. Uhlemann; F. Weller (1992). "3,5-Diphenyl-1,2-dithiolium-hydrogensulfat—Bildung und Struktur" [3.5-Diphenyl-l,2-dithiolium Hydrogensulphate—Synthesis and Structure]. Z. Naturforsch. B (in German). 47 (11): 1501–1504. doi:10.1515/znb-1992-1102. S2CID 95736614.

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