The self-inhibited pyrolysis of isobutane

The pyrolysis of isobutane was investigated in the ranges of 770° to 855°K and 20 to 150 Torr at up to 4% decomposition. The reaction is homogeneous and strongly self‐inhibited. A simple Rice‐Herzfeld chain terminated by the recombination of methyl radicals is proposed for the initial, uninhibited reaction. Self‐inhibition is due to ion of hydrogen atoms from product isobutene giving resonance‐stabilized 2‐methylallyl radicals which participate in termination reactions. The reaction chains are shown to be long. It is suggested that a previously published rate constant for the initiation reaction (1) \documentclass{article}\pagestyle{empty}\begin{document}$$ i - C_4 H_{10} \to CH_3 + i - C_3 H_7 $$\end{document} is incorrect and the value k1 = 1016.8 exp (−81700 cal mol−1/RT)s−1 is recommended. The values of the rate constants for the reactions (4i) \documentclass{article}\pagestyle{empty}\begin{document}$$ CH_3 + i - C_4 H_{10} \to CH_3 + i - C_4 H_9 $$\end{document} (4t) \documentclass{article}\pagestyle{empty}\begin{document}$$ CH_3 + i - C_4 H_{10} \to CH_4 + t - C_4 H_9 $$\end{document} (8) \documentclass{article}\pagestyle{empty}\begin{document}$$ CH_3 + i - C_4 H_8 \to CH_4 + 2 - methylallyl $$\end{document} are estimated to be \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{4i} = 10^{13.16} \exp (- 16300calmol^{ - 1} /RT)cm^3 mol^{ - 1} s^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{4t} = 10^{12.51} \exp (- 12900calmol^{ - 1} /RT)cm^3 mol^{ - 1} s^{ - 1} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{8} = 10^{14.05} \exp (- 17600calmol^{ - 1} /RT)cm^3 mol^{ - 1} s^{ - 1} $$\end{document} From a recalculation of previously published data on the pyrolysis of isobutane at lower temperatures and higher pressures, the value k11c, = 109.6 cm3 mol−1 s−1 is obtained for the rate constant of recombination of t‐butyl. A calculation which is independent of any assumed rate constants or thermochemistry shows that the predominant chain termination reaction is the recombination of two methyl radicals in the conditions of the present work and the recombination of two t‐butyl radicals in those of our previous study at lower temperatures and higher pressures.