Halogeno-sulphonium Salts

The formation of S-halogeno-sulphonium salts from the halogen and a sulphide is in competition with an a-halogenation-oxidation reaction which leads to sulphonyl chlorides when water is present. The initial attack at sulphur may be followed by a Pummerer rearrangement to the adjacent carbon atom, and in the case of unsymmetrical sulphides the regioselectivity is determined by the relative electron density at the a-carbon atoms.  

A mixture of ClCHjSMe and SbClj contains the chloro-sulphonium salts ClCHjSciMe SbClj and CljCHSciMe SbCl , and not the carbonium salts, as previously claimed. However, MeS Clj SbCl is formed from CljCSMe. 

Dialkylamino-alkoxysulphonium salts R2N (OR)Ph BF4 are formed from sulphenamides and an alcohol with Bu OCl and AgBp4 these are conditions which are much milder than those used in the alternative methods of alkylation of sulphinamides. 

Alkoxy-sulphonlum Salts.— Alkylation of sulphoxides by a trialkyloxonium tetrafluoroborate gives these salts, which are relatively stable to air and moisture. The compounds, which are intermediates in one form of the Pummerer rearrangement, are efficient alkylating agents/ The role of methyl phenyl sulphide as the catalytic electron-carrier in an electrochemical oxidation of alcohols is proposed to involve alkoxysulphonium salt formation, followed by a hydride shift/ The fact that some sulphoxide is also formed in this reaction appears to have encouraged the authors in their proposal PhSMe — 2e PhSMe Ph MeOCHR R Ph (CH2X CHR R2 - PhSMe + R COR/ However, there are inconsistencies in the adoption of this mechanism, which has been established for dimethyl sulphoxide in the presence of a proton acceptor, particularly since alcohols are readily oxidized in the same electrochemical system in the absence of a 

Krai and Z. Arnold, Collect. Czech. Chem. Commun., 1978,43, 1248. 

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Halogeno-sulphonium Salts.—Uses for 5-chlorodimethylsulphonium chloride and the corresponding bromine compound have been extended to a conversion of oxirans into ff-halogeno-ketones (Scheme 17), to oxidative dimerization of malonates, and to the conversion of sulphonamides into sulphimides. ... 

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