Atmospheric chemistry of t-CF3CHCHCl: products and mechanisms of the gas-phase reactions with chlorine atoms and hydroxyl radicals

Abstract

FTIR-smog chamber techniques were used to study the products and mechanisms of the Cl atom and OH radical initiated oxidation of trans-3,3,3-trifluoro-1-chloro-propene, t-CF₃CHCHCl, in 700 Torr of air or N₂/O₂ diluent at 296 ± 2 K. The reactions of Cl atoms and OH radicals with t-CF₃CHCHCl occur via addition to the CC double bond; chlorine atoms add 15 ± 5% at the terminal carbon and 85 ± 5% at the central carbon, OH radicals add approximately 40% at the terminal carbon and 60% at the central carbon. The major products in the Cl atom initiated oxidation of t-CF₃CHCHCl were CF₃CHClCHO and CF₃C(O)CHCl₂, minor products were CF₃CHO, HCOCl and CF₃COCl. The yields of CF₃C(O)CHCl₂, CF₃CHClCOCl and CF₃COCl increased at the expense of CF₃CHO, HCOCl and CF₃CHClCHO as the O₂ partial pressure was increased over the range 10–700 Torr. Chemical activation plays a significant role in the fate of CF₃CH(O)CHCl₂ and CF₃CClHCHClO radicals. In addition to reaction with O₂ to yield CF₃COCl and HO₂ the major competing fate of CF₃CHClO is Cl elimination to give CF₃CHO (not C–C bond scission as previously thought). As part of this study k(Cl + CF₃C(O)CHCl₂) = (2.3 ± 0.3) × 10⁻¹⁴ and k(Cl + CF₃CHClCHO) = (7.5 ± 2.0) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ were determined using relative rate techniques. Reaction with OH radicals is the major atmospheric sink for t-CF₃CHCHCl. Chlorine atom elimination giving the enol CF₃CHCHOH appears to be the sole atmospheric fate of the CF₃CHCHClOH radicals. The yield of CF₃COOH in the atmospheric oxidation of t-CF₃CHCHCl will be negligible (<2%). The results are discussed with respect to the atmospheric chemistry and environmental impact of t-CF₃CHCHCl.