Reactions of Methyl Radicals. III. Hydrogen Abstraction from Methyl Acetate and Methyl [²H₃]Acetate

Abstract

A study of hydrogen abstraction by CH₃ radicals from CH₃COOCH₃ in the temperature range 116-224°, and from CD₃COOCH₃ in the range 117-234°, has yielded data on the reactions:

CH₃ + CH₃COOCH₃ → CH₄ + [C₃H₅O₂] (4)

CH₃ + CH₃COOCH₃ → CH₄ + CH₂COOCH₃ (5)

CH₃ + CH₃COOCH₃ → CH₄ + CH₃COOCH₂ (6)

CH₃ + CD₃COOCH₃ → CH₃D + CD₂COOCH₃ (7)

The corresponding rate constants, based dn 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):

logk₄ = (11.56 ± 0.12) - (44430 ± 970)/19.145T (4)

logk₅ = (11.17 ± 0.22) - (42900 ± 1760)/19.145T (5)

logk₆ = (11.44 ± 0.16) - (46980 ± 1290)/19.145T (6)

logk₇ = (11.39 ± 0.04) - (52110 ± 330)/19.145T (7)

At 400 K, 64% of abstraction occurs from the acetyl group, and 36% from the methoxy group. The kinetic isotope effect at 400 K for attack on the acetyl group is 9.6; this is mainly due to a difference in activation energies since the quotient of A factors is close to unity.