Reactions of free radicals with aromatic compounds in the gaseous phase. III. Kinetics of the reaction of methyl radicals with anisole (methoxybenzene)

Abstract

The kinetics of the reaction between methyl radicals and anisole have been studied at temperatures between 453 and 539°K and total pressures between 10 and 30 torr. The concentrations of methyl radicals ranged from 2 x 10^-12 to 5 x 10^-11 mole and those of anisole from 10^-7 to mole cm^-3. The reaction proceeds mainly by the mechanism                    C₆H₅OCH₃+CH₃· → C₆H₅OCH₂·+CH₄                 (1)                  C₆H₅OCH₂·+CH₃· → C₆H₅OC₂H₅                     (2)                          C₆H₅OCH₂· → C₆H₅CHO+H·                   (3) At 487°K attack on the aromatic ring to yield methyl anisoles is about twelve times slower than reaction (1). The Arrhenius parameters for reactions (1) and (8) are: log₁₀(A₁ cm³ mole^-1 sec^-1) = 11.7 ± 0.3, and E₁ = 10.5 ± 0.8 kcal mole^-1; log₁₀(A₈ sec^-1) = 12.5, and E⁸ = 21 kcal mole^-1. The last two values are based on the assumption that the kinetics of reaction (2) are similar to those of the recombination of methyl radicals. The rate of reaction (1) is about half that of the corre- sponding reaction with toluene and about five times that of the reaction with ethane in the above temperature range.