Evidence for a molecular component in the thermal decomposition of azomethane

Abstract

The pyrolysis of a mixture containing 0.432 % azomethane in isobutane has been investigated in the ranges 580–657 K and 50–150 Torr. The high pressure limiting value of the rate constant for CH₃N₂CH₃→ 2CH₃+ N₂(1) has been found to be given by log (k₁/s^–1)= 13.90 ± 0.22 – 193.6 ± 2.5 kJ mol^–1/(2.3RT) in the temperature range 534–657 K from a combination of the results of the present work with previously published values. Below about 50 Torr, values of k₁ diminish in accord with the predictions of unimolecular rate theory.

To provide a simple, self-consistent account of the relationship between values of the rates of formation of methane and of ethane, a small (2 to 3%) molecular component in the thermal decomposition of azomethane is postulated, viz., CH₃N₂CH₃→ C₂H₆+ N₂. (8), The rate constant is found to be given by log (k_s/s^–1)= 11.53 ± 0.59–184.5 ± 7.1 kJ mol^–1/(2.3RT). This hypothesis also accounts for some previously published results. The implications of the occurrence of reaction (8) are discussed.