Reactions of CF3 radicals with benzotrifluoride and the C—H bond strength in C6H5CF3 and C6H6

Abstract

The reactions of CF₃ with benzotrifluoride (BTF) were studied at 1029, 1070 and 1132 K. The R_CF3H/R^½_C2F6[BTF] ratio was found to decrease with increasing benzotrifluoride pressure, which was interpreted as simultaneous formation of C₂F₆ by CF₃ recombination and an inversion reaction between CF₃ and C₆H₅CF₃.

From experiments in the absence and presence of hydrogen, we obtained log(k₂/l. mol^–1 s^–1)=(9.1 ± 0.3)–(9.4 ± 1.2)/θ and log(k₇/l. mol^–1 s^–1)=(8.7 ± 0.1)–(9.3 ± 0.1)/θ, (θ= 2.303 RT/kcal mol^–1) for the rate coefficients of H-abstraction by CF₃ from C₆H₅CF₃ and H₂, respectively. Hence we obtained, with an assumed value for the activation energy of step (–2), D°(CF₃C₆H₄—H)= 109.0 ± 2.5 kcal mol^–1. CF₃H + C₆H₄CF₃→ CF₃+ C₆H₅CF₃(–2)