Atmospheric Chemistry of Tetrachloroethene (Cl₂CCCl₂):  Products of Chlorine Atom Initiated Oxidation

Abstract

The products following Cl atom initiated oxidation of C2Cl4 at 700−760 Torr of air and 230−299 K in the presence and absence of NO x were investigated using three different FTIR smog chamber techniques. There was no measurable effect of temperature on the product yields. CCl3C(O)Cl and COCl2 were formed with molar yields of 68 ± 6% and 77 ± 12% in the presence of NO x and 87 ± 11% and 32 ± 4% in the absence of NO x . These results give branching ratios for the CCl3C(O)Cl and COCl2 forming channels of 0.64 and 0.36 in the presence of NO x and 0.84 and 0.16 in the absence of NO x . Contrary to a recent report by Hasson and Smith (J. Phys. Chem. A, 1999, 103, 2031), variation of the initial C2Cl4 by a factor of 300 over the range (0.016−5.6) × 1014 molecule cm-3 had no discernible effect (<10%) on the product distributions. The different product distribution observed in the presence of NO x may reflect the formation and subsequent decomposition of chemically activated C2Cl5O radicals, formed in the exothermic reaction of C2Cl5O2 with NO. The kinetics of the reaction of Cl atoms with C2Cl4 were measured in 2.0−700 Torr of air at 296 K. The results are in good agreement with the previous study by Nicovich et al. (J. Phys. Chem. 1996, 100, 680). The combined data can be described using F c = 0.6, k o = (1.8 ± 0.3) × 10-28 cm6 molecule-2 s-1 and k ∞ = (4.0 ± 0.4) × 10-11 cm3 molecule-1 s-1. Results are discussed with respect to the atmospheric chemistry of C2Cl4.

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

“…The endproducts of reaction 3 have been studied by several groups. 1,2,17,18 The alkoxy radical CCl 3 CCl 2 O presents two different decomposition pathways, channel 16a leading to the formation of CCl 2 O and channel 16b resulting in the formation of CCl 3 C(O)Cl and Cl atoms, leading to CCl 3 CCl 2 O 2 regeneration.…”

Gas phase oxidation of n-decane and PCE by photocatalysis using an annular photoreactor packed with a monolithic catalytic bed coated with P25 and PC500

“…However such reduction was not observed which may indicate further mechanisms in the photodegradation of PCE besides the classical attack of hydroxyl radicals. Chlorine radicals chain propagation reactions have been a matter of discussion by several research groups in an attempt to explain the PCO mechanism of chlorinated compounds [45][46][47].…”

“…Several authors have followed another meaningful approach to clarify the mechanism of PCE degradation by PCO [45][46][47][48][60][61][62]. However, agreement is yet to be found.…”

“…However, agreement is yet to be found. On one hand, different authors [45][46][47] claimed that Cl • radical addition to PCE occurs several times faster than HO • radical addition, neglecting therefore the role of HO • radical. Such conclusion was further substantiated by Lu et al [61] and Fan and Yates [62] after finding that the surface hydroxyl groups were inactive in the oxidation of methyl chloride and trichloroethylene.…”

Arctic mercury depletion and its quantitative link with halogens

“…Assuming the only loss mechanism for C 2 Cl 4 is reaction with Cl and using the C 2 Cl 4 -O 3 and Hg°-O 3 correlations, we derived order-of-magnitude estimates of f from the DC-8 observational data as a function of the Cl concentration for samples with Hg°exceeding the LOD during AMDEs: Thuner et al (1999). Two points should be noted here.…”