Thermodynamics for the hydrogenation of dicobalt octacarbonyl in supercritical carbon dioxide

Some thermodynamic parameters relevant to hydroformylation catalysis in supercritical media are reported. Equilibrium constants for the hydrogenation of Co{sub 2}(CO){sub 8} to produce HCo(CO){sub 4} in supercritical CO{sub 2} at a gas density of 0.5 g/mL were determined using in situ high-pressure {sup 1}H and {sup 59}Co NMR spectral measurements. van`t Hoff plots for temperatures between 60 and 180 {degrees}C yielded the enthalpy and entropy changes for the reaction, 4.7 {+-} 0.2 kcal/mol and 4.4 {+-} 0.5 cal/(mol{center_dot}K), respectively. The results for the CO{sub 2} medium are close to reported values for liquid n-heptane solutions. The enthalpy and entropy of dissolution of Co{sub 2}(CO){sub 8} in CO{sub 2}, 4.9 {+-} 0.4 kcal/mol and 8 {+-} 1 cal/(mol{center_dot}K), respectively, are also reported. Solubility measurements were facilitated with use of a novel toroid NMR detector, which differs from conventional detectors in its internally confined magnetic flux. This feature allowed selective measurement of gaseous or dissolved species within the detector coil while minimizing interference from undissolved solids or liquids exterior to it. 19 refs., 3 figs., 1 tab.