Methanol reductive carbonylation, a reaction converting methanol to ethanol via acetaldehyde using H2 and CO, presents the initial step of a promising chemical synthesis from C1 building units, which allows the use of more cost effective and renewable resources including biomass. The catalysis with good selectivity was discovered by Wegman and Moloy employing Rh(dppp) (dppp = 1,3-bis(diphenylphosphino)propane) catalyst under milder conditions than that of previous generation Co-based catalysis, but the proposed mechanism does not give insight on how H2 is incorporated into the product as well as inhibitive effects from CO and I- and the superiority of a new set of dppp-based ligand comprising alkoxy binding site recently discovered by Dow Chemical. The mechanism of the reaction was studied by synthesis and characterization of intermediates and related complexes and by kinetic studies utilizing high pressure and variable temperature NMR spectroscopy. The kinetic results indicates the hydrogenolysis is the rate limiting step, and its rate is enhanced by replacing dppp with dpppOEt (dpppOEt = 1,3-bis(di(2-ethylphenyl)phosphino)propane). Among other intermediates, alkoxy-coordinated cationic complexes were also observed directly in the reaction. These results disproved the mechanism based on the formation of Rh-H intermediate, but support mechanism via dissociation of iodide ligand to form cationic intermediate prior to the incorporation of H2, while CO saturates the coordination site of Rh catalyst and slows down the oxidative addition of CH3I.

Mechanistic studies of Rh(diphosphine)-catalyzed methanol reductive carbonylation

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.