Kinetics of the Self-Reactions of Peroxy Radicals Arising from Chlorine-Initiated Oxidation of Chloroethenes

Abstract

The kinetics of the self-reactions of CHCl2CHClO2, CHCl2CCl2O2, and CCl3CCl2O2 have been investigated using a conventional flash photolysis/UV absorption setup at room temperature and at atmospheric pressure. The UV absorption spectra of CHCl2CHClO2, CHCl2CCl2O2, and CCl3CCl2O2 were determined between 230 and 290 nm. All spectra present a broad band centered around 250 nm, with a decrease of cross sections going from the less chlorinated to the more chlorinated radicals. Spectra of CCl3C(O)Cl and CHCl2C(O)Cl, formed in the self-reactions of CCl3CCl2O2 and CHCl2CHClO2, respectively, were also measured between 220 and 290 nm. Values of (3.6 ± 0.9) × 10-12, (7.0 ± 1.5) × 10-12, and (5.0 ± 1.5) × 10-12 (units of cm3 molecule-1 s-1, statistical errors 2σ) have been obtained at 298 K for the rate constants of the self-reactions of CHCl2CHClO2, CHCl2CCl2O2, and CCl3CCl2O2 radicals, respectively. Kinetic analyses of self-reactions were very sensitive to the reaction mechanism used and, in particular, to the way chloroethoxy radicals reacted. Our experimental observations are totally consistent with end-product studies reported in the literature and provide a valuable confirmation of the mechanisms. As the determination of rate constants depends on complex reaction systems, a total uncertainty factor of nearly 2 has been estimated for all rate constants measured, and no clear reactivity trend can be extracted from these data. Nevertheless, we propose for the rate constants of chloroethylperoxy radical self-reactions an average value of (5 ± 2) × 10-12 cm3 molecule-1 s-1 at 298 K.