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 RCF3H/R½C2F6[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).