Radiation-induced addition of hydrogen chloride to ethylene in the gas phase

Abstract

The gas phase addition of hydrogen chloride to ethylene, initiated by γ-radiation, is a free radical chain reaction yielding ethyl chloride (∼99.9 % of the total product at [HCl]/[C₂H₄]∼20). The rate of reaction ∝I[HCl][C₂H₄]^x, where I is the absorbed dose-rate and x varies from 0 to 0.2 as [C₂H₄] is increased, and the overall activation energy = 11.3 kJ/mole. Ethyl chloride inhibits the reaction by competing for chlorine atoms, and sulphur hexafluoride and carbon dioxide (initially) increase the reaction rate by quenching the incipient vibrationally excited chloroethyl radicals more efficiently than hydrogen chloride. The life-time of the excited chloroethyl radical with respect to dissociation is estimated as 2 × 10^–10 sec and this value and the quenching efficiencies of various gases are compared with the results obtained from previous work on the photochlorination of chlorinated olefins. The difference in the values of the overall activation energy between the present work and previous work at much higher pressures can be explained using the excited radical concept.