Mechanism of the reaction of 3SO2 with alkanes

Abstract

The aerosol formed in the photo-initiated reaction between butane (or 2-methylpropane) and sulphur dioxide has been treated with chlorine and the resultant products analysed. The products of the reaction between methyl radicals and sulphur dioxide have also been investigated. These studies show that the principal primary products of the photochemical reaction of sulphur dioxide with alkanes are sulphinic acids RSO₂H together with small yields of the disulphones (RSO₂)₂. On the addition of a solvent the sulphinic acids rearrange very quickly to a variety of secondary products. The sulphinic acids are formed in a non-chain radical sequence initiated by ³SO₂ which abstracts hydrogen from the alkanes to form an alkyl radical and HSO₂·(at 20 °C the primary : secondary : tertiary selectivity is 1 : 4 : 27). The resulting alkyl radical adds reversibly to ground state SO₂ and the sulphonyl radical RSO₂˙ radical either abstracts hydrogen from HSO₂˙ or combines with another sulphonyl radical.