Reactions of trifluoromethyl radicals. III. Hydrogen abstraction from methyl trifluoroacetate, methyl pentafluoropropionate and methyl heptafluorobutyrate

Abstract

Hydrogen abstraction from CF₃COOCH₃, C₂F₅COOCH₃ and C₃F₇COOCH₃ by CF₃ radicals has been studied in the temperature range 100-210º. The rate constants, based on the value of 1013,36 cm³ mol^-1 s^-1 for the recombination of CF³ radicals, are given by (k_n in cm³ mol^-1s^-1, E in kJ mol^-1, R = 0.008314 kJ K^-1 mol^-1): Logk₁ = (10.81 ± 0.16)-(37.52 ± 1.27)/2.303RT Logk₂ = (10.93 ± 0.16)-(38.80 ± 1.32)/2.303RT Logk₃ = (11.24 ± 0.08)-(42.49 ± 0.63)/2.303RT The reactivity of the methoxyl groups in these esters is less than those in HCOOCH₃ and CH₃COOCH₃ by a factor of between 2 and 3. This can be explained in terms of intermolecular polar repulsion induced by the fluorine atoms in the esters and the CF₃ radical.