Thermal decomposition of benzotrifluoride. The C?C bond strength and the heat of formation of the phenyl radical

The kinetics of the decomposition of benzotrifluoride was studied from 720°c to 859°c in a flow system with and without carrier gas. Consideration of the product distribution made possible the study of the decomposition into CF₃ and C₆H₅ radicals, which appeared to be truly homogeneous in character. The first-order rate constant of the C? C bond fission, log k (sec^?1) = (17.9 ± 0.5) (99.7 ± 2.5)/θ, did not change with change of initial concentration, pressure of the carrier gas, or contact time. The Arrhenius parameters have been related to the appropriate thermodynamic data. Assumption of 0 kcal/mole for the activation energy of the reverse combination reaction yielded DH(C₆H₅? CF₃) = 103.6 ± 2.5 kcal/mole and ΔH(C₆H₅) = 77.1 ± 3.0 kcal/mole. Applicability of the simple first-order formula to calculation of the rate constant has been also dealt with.