  The nature of the CH2Cl2 neutral/acidic hydrolysis reaction from ambient to
supercritical conditions (25 C to 600 C at 246 bar) is explored. Of primary
interest is the effect of the changing dielectric behavior of the water solvent
over this temperature range on this reaction. Experiments reveal that
significant CH2Cl2 hydrolysis occurs under subcritical temperatures, while
relatively little hydrolysis occurs under supercritical conditions. These
trends cannot be explain 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 profile
with a decreasing dielectric constant provide a mechanism for a slowing of the
reaction at higher temperatures by as much as three orders of magnitude. These
solvent effects are captured quantitatively in a correction factor to the
Arrenius form of the rate constant, which is incorporated into a global rate
expression proposed for CH2Cl2 hydrolysis that provides good predictions of the
experimental data.
