Dimeric cations from alkanesulphenyl chlorides. The elusive nature of sulphenylium ions

Abstract

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.