Arrhenius parameters for the reaction of trifluoromethyl radicals with cyanogen chloride

Abstract

The reaction of CF₃ radicals with ClCN has been studied over a wide temperature range, 268–293 K, using CF₃ radicals generated by the photolysis of CF₃I. Over the range 408–473 K, CF₃COCF₃ was also used as a CF₃ radical source. The radicals react with ClCN by addition followed by decomposition of the adduct and by chlorine abstraction: CF₃+ ClCN ⇌ CF₃ClCN (1), (– 1), CF₃ClCN → CF₃Cl + CN (2), CF₃+ ClCN → CF₃Cl + CN (3), 2 CF₃ [graphic omitted] C₂F₆. The Arrhenius plot for this reaction is strongly curved. Using data from the low- and high-temperature regions, the following expressions for the rate constants for addition reaction (1) and chlorine abstraction (3) relative to CF₃ recombination have been obtained: log[(k₁/k^½_c)/cm mol^–½s^½]= 3.75 – 26.55 kJ mol^–1/2.303 RT, log[(k₃/k^½_c)/cm mol^–½s^½]= 6.43 – 48.61 kJ mol^–1/2.303 RT. The combination of E₁ with the difference E_–1–E₂, which can be estimated, gives an upper limit for ΔH^°₃ from which an approximate value for ΔH^°_f(CN) of 393.4 kJ mol^–1 or less has been obtained.