Synthesis of Disulfonium Dications

Addition of 1,5-dithiacyclooctane to zeolite CaY in the presence of molecular oxygen results in spontaneous oxidation to mono- and bis-sulfoxides through formation of the corresponding radical cation characterized by ESR and diffuse reflectance of UV-Vis spectroscopy.51 

2 Interaction of H2SO4 with Mono-S-Oxides of bis-Sulf-ides 

The second main approach to disulfonium dications is based on nucleophilic substitution at sulfonium sulfur atom by a sulfide. This approach is much more efficient and versatile than the direct oxidation of sulfides.59 61 

Oae and Numata26 were the first to postulate formation of a disulfonium dication in reaction of concentrated sulfuric acid with monosulfoxide of a bis-sulfide. Later Furukawa et al.62 found that the crystalline hydrosulfate 36 can be prepared by reaction of the corresponding monosulfoxide 13 (or A-tosyli-mide 14) with concentrated sulfuric acid. Formation of a symmetric dication 38 was confirmed by isolation of 1 1 mixture of deuterated sulfoxides 37 and 39 

In agreement with this relatively complicated picture, the and 13C NMR spectra of a S-S dication formed from 1,4-dithiane by this method are more complex than expected for such a symmetric molecule.65 This observation can also be explained by equilibrium of dications with intramolecular and 

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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One can use the same methods for generation of trithiodications as for synthesis of disulfonium dications, i.e. oxidation of suitable trisulfides with concentrated sulfuric acid or with nitrosonium salts as well as reaction of a... 

Common synthesis of disulfonium dications involves formation of a S-S bond by oxidative coupling of two sulfide moieties. Involving for oxidative generation of S-S bond, thiocarbonyl compounds can lead to new-type dications containing disulfide moieties between two positively charged fragments. There are several disulfide dications of this type derived from thioureas, thiocarbon-ates and thioketones as well as selenium derivatives.137 148... 

The turning point in the understanding of the chemical nature of S-S dications came in 1976 when Musker reported synthesis, isolation and characterization of disulfonium dication 12 formed by the two-electron oxidation of 1,5-dithiacyclooctane 10 (Scheme 4).29,30... 

The most versatile approach to disulfonium dications - reaction of triflic anhydride with monosulfoxides of bis-sulfides - has certain limitations in the case of selenium. Most importantly, selenoxides that contain (3-hydrogen atoms are labile.120 122 Trimethylsilyl triflate was used instead of triflic anhydride for synthesis of dication 112 from a selenoxide 111 (Scheme 43).123... 

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