UNIQUE PRESSURE EFFECTS ON THE ABSOLUTE KINETICS OF TRIPLET BENZOPHENONE PHOTOREDUCTION IN SUPERCRITICAL CO2

Laser flash photolysis studies of the hydrogen atom abstraction reaction of triplet benzophenone from 2-propanol and 1,4-cyclohexadiene in supercritical CO2 reveal unusual pressure effects on absolute rate constants. Monitoring reactivity close to the critical temperature (T(c)) revealed that bimolecular rate constants increase sharply with a decrease in pressure, approaching the critical point. Kinetic investigations along an isotherm further removed from T(c) and predictive calculations on the pressure effect expected in supercritical CO2 indicate that enhanced reactivity is due to local substrate clustering.