Hydrogen isotope exchange between pentafluoroethane and water: Kinetics and equilibrium

It is shown experimentally that pentafluoroethane undergoes rapid protium-deuterium exchange with water in the presence of hydroxide ion. Addition of dimethylsulfoxide enhances the rate at least by a factor of 100. The first measured fractionation factor data are presented for the temperature range of 50-120 degrees C. These values are compared with the theoretical estimations calculated by using isotopic reduced partition function ratios based on molecular vibrational frequencies. Although catalytic exchange is slow at ambient temperature, the reaction rate becomes measureable above around 60 degrees C because of large activation energy (92 kl/mole). Comparisons are made with similar data available for various halomethane and haloethane systems. (C) 1997 John Wiley & Sons, Inc.