The mechanism of the isomerisation of dimethyl sulphite to methyl methanesulphonate

The isomerisation of dimethyl sulphite to methyl methanesulphonate is catalysed by the methanesulphonate ion. The reaction appears to proceed in two stages. First, dimethyl sulphite alkylates the methanesulphonate ion to form methyl methanesulphonate and methyl sulphite ion. The isomerisation is then completed by the alkylation of the methyl sulphite ion at the sulphur atom by methyl methanesulphonate.Other anions, which can accept a methyl group to give a strong alkylating agent, also catalyse the reaction.