Thianthrene dication formation

Cation radicals may be oxidized further, and some of them become stable dications. This process is often characterized as the second wave in two successive anodic one-electron oxidations. The thianthrene dication is now well known (Shine and Piette, 1962 Hammerich and Parker, 1973), but has not been isolated. On the other hand, the dipcrchloratc of 2,3,7,8-tetramethoxythianthrene dication is a blue solid (Glass el al., 1973). Dications of some aromatics which are well-known for forming stable cation radicals (e.g. perylene) have been made in FS03H-SbF5 solution (Brouwer and van Doom, 1972). Irradiation of hexachlorobenzcne cation radical in SbFs-Cl2 causes the formation of the dication (in this case, a triplet state) (Wasserman et al., 1974). Oxidation of metallo-porphyrin cation radicals to stable (but reactive) dications is quite common (Dolphin et al., 1973). 

Redox processes involving 178 have also been studied.Anodic oxidation of thianthrene has been eifected in a wide variety of solvents. Use of trifluoracetic acid gives stable solutions of 178 and, if perchloric acid is included, the solid perchlorate salt may be isolated on evaporation of the solvent after electrolysis. Dichloromethane at low temperatures has been used and, at the opposite extreme, fused aluminum chloride-sodium chloride mixtures. " Propylene carbonate permits the ready formation of 178, whereas the inclusion of water in solvent mixtures gives an electrochemical means of sulfoxidizing thianthrene. Reversible oxidation of 178 to thianthrenium dication may be brought about in customary solvents such as nitriles, nitro compounds, and dichloromethane if the solvent is treated with neutral alumina immediately before voltammetry addition of trifluoracetic anhydride to trifluoracetic acid equally ensures a water-free medium. The availability of anhydrous solvent systems which permit the reversible oxidation and reduction of 178 has enabled the determination of the equilibrium constants for the disproportionation of the radical and for its equilibria with other aromatic materials. ... 

A more detailed study" has shown that this oxidation occurs as a stepwise process with the second oxidation potential 20 mV lower than the first. Such anomalous electrochemical behavior of 10 presents more evidence for the formation of a S-S dication." The first evidence that 10 can be oxidized chemically to a stable disulfonium dication was obtained by Shine and Kette." While investigating the oxidative properties of the thianthrene radical cation... 

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