Oxygen-assisted cross-coupling of methanol with alkyl alcohols on metallic gold

We demonstrate for the first time that selective cross-coupling of methanol with either ethanol or n-butanol occurs below room temperature on metallic gold with no metal oxide support in a reaction sequence that occurs entirely on the surface. The esterification proceeds via activation of the alcohols by adsorbed oxygen and a sequence of reactions that involve both surface-bound alkoxys and hemiacetals as intermediates. The reaction selectivity is dictated by competing beta-hydride elimination from the alkoxys. Due to the higher activation energy for beta-hydride elimination from methoxy, no formate esters are formed. A molecular-scale mechanism constructed using our results is in excellent agreement with studies of heterogeneous catalysts, providing insight into selectivity control under a broad range of conditions.