Elena V. Oexler

Arrhenius parameters for the reaction of trifluoromethyl radicals with cyanogen chloride

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.

The gas-phase reaction of CF3 radicals with HCN in the temperature range 333-523 K

The reaction of CF3 radicals produced by photolysis of CF3I with HCN has been investigated in the temperature range 333–523 K. The radicals react with HCN by addition followed by a sequence of reactions of which the most important are: CF3+ HCN ⇆ CF3HCN (1,–1), CF3+ CF3HCN → HCF3CNCF3(2), CF3+ CF3HCN → CF3H + CF3CN(3), I + CF3HCN → HI + CF3CN (4) 2 CF3 [graphic omitted] C2F6. Arrhenius parameters for the addition reaction relative to radical recombination were estimated from experiments at conversions [graphic omitted] 3% in the temperature range 333–453 K. The best fit to our experimental results gave log[(A1/A1/2c) cm3/2 mol–1/2 s–1/2]= 4.97 and E1–½Ec= 30.9 kJ mol–1, with systematic estimated errors of up to 0.3 and 2.4 kJ mol–1, respectively. These parameters are compared with those obtained for other addition reactions of these radicals to substrates with a triple bond.