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/k½c)/cm mol–½s½]= 3.75 – 26.55 kJ mol–1/2.303 RT, log[(k3/k½c)/cm mol–½s½]= 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.