Hydrocarbon formation from methanol and dimethyl ether. A review of the experimental observations concerning the mechanism of formation of the primary products

In recent years a considerable amount of research effort has been directed at gaining an understanding of the mechanism of the formation of the primary products in the methanol conversion reaction. This paper reviews the experimental data accumulated to date and discusses the mechanisms that have been proposed with respect both to the formation of the initial carbon-carbon bond and the formation of methane. Four mechanisms are discussed in detail, namely: (a) formation of a carbene from methanol by α-elimination, (b) intermolecular reaction of dimethyloxonium methylide (c) involvement of a radical pathway and (d) deprotonation of a surface bonded methyloxonium ion to give a surface-bonded oxonium methylide. These mechanisms are discussed against the background of the experimental data that has been obtained either against or in support of these proposals.