Atmospheric chemistry of (Z)-CF3CHCHCl: products and mechanisms of the Cl atom, OH radical and O3 reactions, and role of (E)–(Z) isomerization†
The chemical mechanisms of the OH radical, Cl-atom and O3 initiated oxidation of (Z)-CF3CHCHCl were studied at 296 ± 1 K in 10–700 Torr air of N2/O2 diluent. Cl atoms add to the CC double bond: 12 ± 5% to the terminal carbon and 85 ± 5% to the central carbon. In 700 Torr of air the products are CF3CHClCHO, HCOCl, CF3COCl, CF3CHO, (E)-CF3CHCHCl, CF3C(O)CHCl2, and CF3CHClCOCl. The yield of (E) isomer was dependent on total pressure, but independent of O2 partial pressure; consistent with isomerization occurring via Cl atom elimination from the chemically activated rather than the thermalized CF3CHCHCl–Cl adduct. The rate constant for (Z)-CF3CHCHCl + Cl was measured at low pressure (10–15 Torr) and found to be indistinguishable from that determined at 700 Torr total pressure, whereas the low pressure rate constant for (E)-CF3CHCHCl was 36% smaller. G4MP2 ab initio calculations showed that the (E) isomer is 1.2 kcal mol−1 more stable than the (Z) isomer. Cl atom elimination from the adduct will preferentially form the (E) isomer and hence the rate of CF3CHCHCl loss will be more sensitive to pressure for the (Z) than the (E) isomer. Reaction of (Z)-CF3CHCHCl with OH radicals gives CF3CHO, HCOCl, (E)-CF3CHCHCl, and HCl. A significant chlorine atom elimination channel was observed experimentally, and supported by computational results. The oxidation products of the reaction of O3 with (Z)- and (E)-CF3CHCHCl were determined with no evidence of isomerization. The results are discussed with respect to the atmospheric chemistry and environmental impact of (Z)- and (E)-CF3CHCHCl.