Trialkylsulphonium salts

Additional evidence for this mechanism is provided by the observation that whereas simple trialkylsulphonium salts R3S+X, are poor initiators for the polymerisation, 2-thia-alkyl sulphonium salts give rise to polymerisations having characteristics similar to the second stage described previously (53), i.e. 

Dialkyl sulphides are converted into trialkylsulphonium salts by treatment with an alkyl halide (the bromide or iodide is usually the reactant of choice). An important example of this group is trimethylsulphonium iodide, which is used as a methylene transfer reagent by virtue of its being converted in the presence of base into a sulphur ylide, which is a nucleophilic carbene equivalent. 

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