ABSTRACT:

Cobalt carbonyl hydride catalyzed hydrogenation of carbon monoxide in a homogeneous supercritical carbon monoxide medium is reported for the first time. The reaction rate and products and the cobalt containing species associated with the catalytic reaction were measured in situ at 180 and 200 oC and at total pressures of hydrogen and carbon monoxide near 260 atm using a high-pressure nuclear magnetic resonance (NMR) probe. The second order rate constant at 200 oC, 12 x 10-8 s-1 atm-1, measured in supercritical carbon monoxide is close to the reported value for the nonpolar solvent, benzene (15 x 10-8 s-1 atm-1) and considerably smaller than that reported in the more polar solvent, 2,2,2-trifluoroethanol (84 x 10-8 s-1 atm-1). The products of the reaction including methanol and methyl formate were quantified by in situ 1H NMR, while in situ 59Co NMR revealed cobalt carbonyl hydride and dicobalt octacarbonyl as the only detectable cobalt species. Separate experiments established that the homologation of methanol, the pathway for production of higher alcohols under CO hydrogenation conditions in polar solvents, did not occur to a measurable extent in the nonpolar supercritical CO
medium used here.