SOLVATION EFFECTS ON REACTIONS OF TRIPLET BENZOPHENONE IN SUPERCRITICAL FLUIDS

Laser flash photolysis of the hydrogen abstraction reaction of triplet benzophenone ((BP)-B-3) from 2-propanol and 1,4-cyclohexadiene in sup ercritical ethane and fluoroform was investigated. Bimolecular rate co nstants based on bulk concentrations decrease with an increase in pres sure along both isotherms studied. These results corroborate our previ ous studies in CO2 that show increased reaction rates due to enhanced local compositions of cosolvent around the (BP)-B-3 solute. Analysis o f the results includes prediction of the thermodynamic pressure effect on the rate constant, which suggests an increase in the rate constant with pressure, as well as the effects of increased local cosolvent co ncentrations about (BP)-B-3. Spectroscopic measurements of the local c omposition of 2-propanol about a solute in supercritical CO2 are used to explain the apparent discrepancy between experiment and prediction, providing reasonable evidence that the local environment can influenc e kinetically controlled reactions in supercritical fluids.