PROPYLENE HYDROFORMYLATION IN SUPERCRITICAL CARBON-DIOXIDE

The cobalt carbonyl catalyzed hydroformylation of propylene and related equilibrium and dynamic processes were investigated by means of high-pressure NMR spectroscopy with supercritical carbon dioxide (d = 0.5 g/mL) used as the reaction medium to avoid gas/liquid mixing problems associated with conventional solvents. At 80-degrees-C, the hydroformylation proceeds cleanly in CO2, giving a somewhat improved yield of linear to branched butyraldehyde products, 88%, without use of stirring. The rate of propylene hydroformylation and in situ measurements of the steady-state concentrations of catalytic intermediates [RC(O)Co(CO)4, HCo(CO)4, and Co2(CO)8] were found to be comparable to values for other linear-terminal olefins in nonpolar liquid media. For the hydrogenation of Co2(CO)8 (to form HCo(CO)4) at 80-degrees-C in CO2, the equilibrium constant, Kp = 8.8 x 10(-4) M atm-1, and the rate constants for the forward and reverse reactions (1.6 x 10(-6) atm-1 s-1 and 1.8 x 10(-3) M-1 s-1, respectively) compared closely with values for liquid methylcyclohexane solutions. Potential dynamic processes involving Co2(CO)8, Co4(CO)12, or HCo(CO)4 were explored at temperatures up to 205-degrees-C at 338 atm by means of Co-59, C-13, and H-1 NMR spectroscopy. Due to the low viscosity of the supercritical medium, linewidths for the Co-59 nucleus were decreased by a factor of about 6 compared to values in normal liquids. An NMR pressure-probe design that uses an efficient toroid detector is also described.