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A 1H n.m.r. study of the reaction between alkanesulphenyl chlorides and dialkyl disulphides in sulphur dioxide in the presence of Lewis acids and in strong acids (FSO3H or 98% of H2SO4) led to the characterization of alkyl-(bisalkylthio)sulphonium ions R[graphic omitted](SR)2(1). Results of conductimetric and 1H n.m.r. experiments at low temperatures suggest that the formation of (1) also occurs to a large extent in the absence of Lewis acids. It was observed that ions (1) are also formed from disulphides by the action of strong acids.

Conductimetric and 1H n.m.r. evidence on the formation of alkyl(alkylthio)(chloro)sulphonium ions [R[graphic omitted](Cl)SR] by reaction of methane and ethanesulphenyl chlorides in liquid sulphur dioxide with Lewis acids (SbF5, BCl3, SbCl3,BF3) is reported. In the presence of BCl3 or BF3 dynamic behaviour in the n.m.r. spectra leading to the equivalence of the two alkyl groups is observed. This is explained by attack of chloride ion on the sulphonium salts and their dissociation into sulphenyl chlorides. The n.m.r. and conductimetric behaviour of the sulphenyl chlorides suggests that partial ionization into alkyl(alkylthio)(chloro)sulphonium ions may occur even in the absence of added Lewis acids. Sulphonium ions are also formed in 98% sulphuric acid and fluorosulphuric acid. Under no conditions was an indication of the presence of sulphenylium ions (RS+) found.