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.

Environmental effects of large igneous province magmatism: a Siberian perspective

“…The reported data are in very good agreement between 242 and 300 nm, where the data of Villenave et al [821] are smaller by 1-10% than the data of Libuda [445]. At shorter wavelengths the absorption cross-sections reported by Libuda [445] become smaller by up to ~25% at 235 nm than those reported by Villenave et al [821]. The latter authors observed a minimum near 232 nm and increasing cross-sections between 230 and 220 nm.…”

“…In the wing of the absorption band above 290 nm the data reported by Libuda [445] become smaller by up to about 70% than the data reported by Gillotay et al [282]. Since the data of Villenave et al [821] and Gillotay et al [282] are in good agreement, but Villenave et al [821] measured absorption cross-sections at 10-nm increments only, we list in Table 4-130 the room temperature data of Gillotay et al [282], which are averages over the 500-cm -1 and 5-nm intervals of the high-resolution spectrum (0.015 nm) generally used in stratospheric photodissociation calculations. The temperature studies at 210-295 K by Gillotay et al [282] show an increase of the absorption crosssections with increasing temperature all over the observed wavelength region.…”

“…Above 315 nm the data points show a somewhat irregular behavior. We therefore recommend the 1-nm averages of Libuda's [445] medium-resolution (0.6 nm) data for the region 235-316 nm, which are listed in Table 4 [821]. An absorption band with the maximum around 258 nm was observed in that wavelength region.…”

“…At longer wavelengths the absorption curve reported by Libuda [445] shows a regular behavior up to 316 nm. In Table 4-129 are listed as a recommendation the absorption cross sections measured at 10-nm increments for 200-300 nm by Villenave et al [821]. [445] is very shallow in the region 240-270 nm, it crosses the other two curves at ~245 nm and is higher by 30-40% at 235 nm and lower by 10-14% in the region of the maximum.…”

Reactions of chloroethenes with atomic chlorine in air at atmospheric pressure

“…Earlier, 5 we have studied kinetics of recombination of peroxy radicals (CHCl 2 CHClO 2 , CHCl 2 CCl 2 O 2 , and CCl 3 CCl 2 O 2 ) formed in the chlorine initiated oxidation processes of 1,2 di chloroethene, trichloroethene, and tetrachloroethene, respectively. However, the question about the reac tion products remained open.…”