Kinetics of the homogeneous catalytic hydroformylation of 1-octene in supercritical carbon dioxide with HRh(CO) [P(p-CF3C6H4)(3)](3)

The first kinetic study of the rhodium-catalyzed homogeneous hydroformylati on of olefins in supercritical carbon dioxide (scCO(2)) is reported. The hy droformylation of 1-octene using HRh-(CO)[P(p-CF3C6H4)(3)](3) (1) in scCO(2 ) was investigated at 50 degrees C and 273 atm. A kinetic rate expression w as developed to represent the experimental data, having the form r(1-octene ) = kA(0.48)C(0.84)D(0.50)/(1 + KBB2.2), where A = [H-2], B = [CO], C = [1] , and D = [1-octene]. The observed kinetic behavior differs significantly f rom behavior of conventional systems employing the nonfluorinated analogue of 1, HRh(CO)(PPh3)(3), in organic solvents. Most notable are the similar t o 0.5 order Ha dependence of the reaction rate, the lack of substrate inhib ition, and the absence of a critical catalyst concentration. The altered ki netic behavior relative to conventional systems may be due to scCO(2) solve nt effects, the modified phosphine ligand, or the high concentrations of re actant gases in the system. This study also illustrates the usefulness of s cCO(2) as a mechanistic tool in homogeneous catalysis, especially for react ions involving gases such as H-2 and CO.