Kinetics of methylene chloride hydrolysis and the salt effect under hydrothermal conditions

The reaction progress of methylene chloride under hydrothermal conditions w as pursued using a corrosion-resistant flow reactor made from titanium tubi ng, paying attention to minimize the contribution of the preheating zone fo r the reaction. The relation between the CH2Cl2 conversion and residence ti me showed that the hydrolysis is first order in CH2Cl2. The rate constant i ncreased monotonically as the temperature was raised but dropped to a large extent above the critical temperature. A relatively small increase of the rate constant was observed in the presence of NaCl under 360 degreesC. The kinetic behavior could be explained based on a S(N)2 mechanism under subcri tical conditions, and the sudden drop of the rate constant at the critical point was attributed to the abrupt decrease of the dielectric constant of w ater. The salt effect wats also analyzed along the same context. The reacti on rate and the detailed reaction progress, however, under supercritical co nditions are not yet fully understood.