Alternative pathways in the ruthenium catalysed hydrogenation of CO to alcohols

CO hydrogenation in [PBu 4 ]Br in the presence of [Ru 3 (CO) 12 ] gives predominantly methanol, ethanol and propanol with small amounts of 1,2-ethanediol. Using RuO 2 as the catalyst precursor, the same products are formed along with higher alcohols (1-butanol -1-heptanol). Reactions carried out using added 13 CH 3 OH or 13 CO show that ethanol and propanol come from homologation reactions of methanol and ethanol respectively, but that the higher alcohols are not formed through the lower alcohols as intermediates. Labelling studies show that lower alcohols formed from CO hydrogenation in the presence of ruthenium precursors arise from methanol homologation, but higher alcohols do not involve incorporation from methanol, rather being formed only from CO/H 2 in the gas phase.