A mechanistic explanation for selectivity in the conversion of methanol to 2,2,3-trimethylbutane (triptane): Moderate acidity allows kinetic control to operate

Methanol is converted to hydrocarbons by reaction with ZnI2 or InI3 at 200 °C, with surprisingly high selectivity (yields on the order of 20%) to a single highly branched alkane, 2,2,3-trimethylbutane (triptane). Mechanistic studies demonstrate that the previously proposed mechanism, which proceeds via a carbocation-based route that involves methylation of olefins and hydride transfer to carbocations, can account quantitatively for the selectivity. Differences in product distribution between the Zn- and In-based systems represent quantitative, not qualitative, differences in behavior, and can be attributed to the slightly higher effective acidity of the latter.