Kinetics and mechanism of the thermal gas-phase reaction between trifluoromethylhypofluorite, CF3OF, and trichloroethene

Abstract

The thermal gas-phase addition of CF₃OF to CHClCCl₂ has been studied between 284 and 324.0 K. The initial pressure of CF₃OF was varied between 7 and 57.8 Torr [1 Torr =(101 325/760) Pa] and that of CHClCCl₂ between 3.4 and 45 Torr. CF₃O(CHClCCl₂)F was the main product. Other products, formed in minor amounts, were CHClFCCl₂F and CF₃O(CHClCCl₂)_n2OCF₃.

The reaction was a homogeneous chain reaction not affected by the total pressure. In the presence of O₂ the oxidation of trichloroethene to CHCl₂C(O)Cl occurred. Introduction of CCl₃F to the reaction system initiated the addition of this halomethane to trichloroethene.

The basic steps of the reaction were: generation of radicals CF₃O˙ and CHClFCCl^˙₂ in the bimolecular process between CF₃OF and CHClCCl₂, (rate constant k₁), generation of telomeric radicals CF₃O(CHClCCl₂)˙ by addition of CF₃O˙ to trichloroethene, abstraction of fluorine atom from CF₃OF by CHClFCCl₂˙ and CF₃O(CHClCCl₂)˙, (rate constant k₄), polymeric chain propagation by further successive additions of telomeric radicals to another molecule of trichloroethene, (rate constant k₅), and recombination of telomeric radicals.