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 (ks/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.