Hydrogen abstraction from (²H₃)methyl acetate by methyl and trifluoromethyl radicals

Abstract

A study of hydrogen abstraction from CH₃COOCD₃ by CH₃ radicals in the temperature range 113-232º, and by CF₃ radicals in the range 83-212º, has yielded data on the reactions:

CH₃+CH₃COOCD₃ → CH₄+CH₂COOCD₃ (1)

CH₃+CH₃COOCD₃ → CH₃D+CH₃COOCD₂ (2)

CF₃+CH₃COOCD₃ → CF₃H+CH₂COOCD₂ (3)

CF₃+CH₃COOCD₃ → CF₃D+CH₃COOCD₂ (4)

The corresponding rate constants, based on the values 10^13.34 and 10^13.36 cm³ mol^-1 s^-1 for the recombination of CH₃ and CF₃ radicals, respectively, are given by (k in cm³ mol^-1 s^-1 and E in J mol^-1):

logk₁ = (11.31±0.12)-(43500±1030)/19.145T (1)

logk₁ = (11.31±0.12)-(53460±640)/19.145t (2)

logk₃ = (11.12±0.06)=(34260±450)/19.145T   (3)

logk₄ =(10.93±0.12)-(38650±900)/19.145T (4)

These results lead to kinetic isotope effects at 400 K for attack on the acetyl group of 11, for the CH₃ reaction, and 24, for the CF₃ reaction, thus confirming the values we obtained previously. For attack on the methoxy group, the kinetic isotope effects are 8 and 4, for the CH₃ and CF₃ reactions, respectively.