Reactions of Methyl Radicals. II. Hydrogen Abstraction from Methyl Trifluoroacetate

Abstract

Hydrogen abstraction from CF₃COOCH₃ and CH₃COCH₃ by CH₃ radicals

CF₃ + CF₃COOCH₃ → CH₄ + CF₃COOCH₂ (1)

CF₃ + CF₃COOCH₃ → CH₄ + CH₃COCH₂ (3)

has been studied in the temperature range 117-244º. The rate constants, based on the value of 10^13.34 cm³ mol^-1 s^-1 for the recombination of CH₃ radicals, are given by (k in cm³ mol^-1 s^-1 and E in J mol^-1) :

logk₁ = (10.39 ± 0.11)- (37680 ± 880)/19.145T

logk₃ = (11.53 ± 0.02)- (40590 ± 170)/19.145T

CF₃COOCH₃ is less susceptible to attack by CH₃ radicals than by CF₃ radicals by a factor of 2.8 at 400 K, due mainly to a difference in A factors, since the activation energies of the two reactions are almost identical. These results can be rationalized in terms of intermolecular polar repulsion between the CF₃ radical and CF₃COOCH₃.