SOLVATION EFFECTS ON KINETICS OF METHYLENE-CHLORIDE REACTIONS IN SUBCRITICAL AND SUPERCRITICAL WATER - THEORY, EXPERIMENT, AND AB-INITIO CALCULATIONS

The nature of the CH2Cl2 neutral/acidic hydrolysis reaction from ambie nt to supercritical conditions (25 to 600 degrees C at 246 bar) is exp lored. Of primary interest is the effect of the changing dielectric be havior of the water solvent over this temperature range on this hydrol ysis reaction. Experiments reveal that significant CH2Cl2 hydrolysis o ccurs under subcritical temperatures, whereas relatively little hydrol ysis occurs under supercritical conditions. These trends cannot be exp lained by simple Arrhenius behavior. A combination of Kirkwood theory and ab initio modeling provides a means of successfully accounting for this behavior both qualitatively and quantitatively. The results show that increases in the activation energy and a changing reaction profi le with a decreasing dielectric constant provide a mechanism for a slo wing of the reaction at higher temperatures by as much as 3 orders of magnitude. These solvent effects are captured quantitatively in a corr ection factor to the Arrhenius form of the rate constant, which is inc orporated into a global rate expression proposed for CH2Cl2 hydrolysis that provides good predictions of the experimental data.