Abstract
The pyrolysis of 1‐ and 2‐nitropropane highly diluted in Ar has been studied in shock waves at temperatures K 915 < T < 1200 K and total gas concentrations 7 · 10^−6^ mol cm^−3^ < [Ar] < 1.5 · 10^−4^ mol cm^−3^. The reactions behind the shock waves have been followed by recording light absorption‐time profiles of the decomposing molecules and the produced NO~2~ Under the conditions of the experiments, the primary reaction step in both cases is the CN bond:fission: \documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{rcl} {\rm 1} - {\rm C}_{\rm 3} {\rm H}_{\rm 7} {\rm NO}_{\rm 2} {\rm (} + {\rm M)} &\to & n - {\rm C}_{\rm 3} {\rm H}_{\rm 7} + {\rm NO}_{\rm 2} {\rm (} + {\rm M)\quad k} = 2.3 \cdot 10^{15} {\rm exp }(- 55{\rm kcal mol}^{ - 1} /{\rm RT}){\rm s}^{ - 1} \ 2 - {\rm C}_{\rm 3} {\rm H}_{\rm 7} {\rm NO}_{\rm 2} {\rm (} + {\rm M)} &\to & i - {\rm C}_{\rm 3} {\rm H}_{\rm 7} + {\rm NO}_{\rm 2} {\rm (} + {\rm M)\quad k} = 2.4 \cdot 10^{15} {\rm exp }(- 54{\rm kcal mol}^{ - 1} /{\rm RT}){\rm s}^{ - 1} \ \end{array} $\end{document} (first order rate constants k measured at concentrations of [Ar] ≃ 10^−4^ mol cm^−3^).
At these concentrations the reactions are near to the high pressure limit. By varying the Ar‐concentrations over one order of magnitude, only a slight pressure dependence was found. Reaction mechanisms which account for NO~2~ removal are discussed.