Kinetics of $$dot NO_2$$ formation upon the decomposition of nitromethane behind shock waves and the possibility of nitromethane isomerization in the course of the reaction

The decomposition of nitromethane behind shock waves was studied at T = 1190–1490 K and P ≈ 1.5 atm; the reaction was monitored based on the formation and consumption of [(N)dot]O₂dot NO_2, radicals, which were detected by their absorption in the region of λ = 405 nm. It was found that the curves of the yield of [(N)dot]O₂dot NO_2 have a convex shape, which is characteristic of the formation of primary decomposition products. Based on an analysis of the initial sections of the experimental curves of the yield of [(N)dot]O₂dot NO_2, the temperature dependence of the rate constants of formation of these radicals upon the decomposition of nitromethane was found for the first time: k₁ ([(N)dot]O₂ ) = (6.3 ±2) ×10¹² exp( - 48.9 ±2/RT)s ^{- 1}k_1 (dot NO_2 ) = (6.3 pm 2) times 10^{12} exp ( - 48.9 pm 2/RT)s^{ - 1} (the dimensionality of E _a is kcal/mol). It was found that the rate constants of nitromethane decomposition measured from the consumption of the parent substance and the yield of [(N)dot]O₂dot NO_2 radicals almost coincide with each other. A kinetic simulation of the formation and consumption of [(N)dot]O₂dot NO_2 upon the decomposition of nitromethane was performed. A good agreement between experimental and calculated data was achieved. A brief theoretical analysis of competition between the channels of direct disintegration and isomerization under conditions of the thermal decomposition of nitromethane was performed. The advantage of the direct disintegration channel with the rupture of the C-N bond was shown. Both experimental and published data on the isomerization of nitromethane into methyl nitrite upon its thermal decomposition and photolysis were analyzed.