ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The pyrolysis of n-hexane has been investigated in the ranges 723-823 K and 10-100 Torr at up to 3% decomposition. The reaction is homogeneous and free from the self-inhibition by olefin products observed for several other alkanes. The products of the reaction are hydrogen, methane, ethane, ethene, propene, but-1-ene, and pent-1-ene, with smaller amounts of propane. It is shown that the results are in quantitative agreement with a conventional Rice-Herzfeld chain mechanism terminated by the combination and disproportionation of ethyl radicals, but with the mechanism extended so as to include the unimolecular isomerizations via a six-membered cyclic transition state between 1-hexyl and 2-hexyl (1-methylpentyl) radicals.The overall rate constant of initiation is estimated to be given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log(}k_1 /{\rm s}^{ - {\rm 1}}) = 17.77 - (83.8\,{\rm kcal\, mol}^{ - {\rm 1}})/(2.3{\rm }RT) $$\end{document} The rate constant for the reaction is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \log (k_9 /{\rm cm}^{\rm 3}\, {\rm mol}^{ - 1} {\rm s}^{ - 1}) = 13.30 - (17.9{\rm \, kcal\, mol}^{ - 1})/(2.3{\rm }\,RT) $$\end{document} which when combined with published data gives an Arrhenius plot curved upwards at low values of 1/T as has been observed for several other hydrogen abstraction reactions of methyl and of ethyl. Estimates are made of rate constants and ratios of rate constants for several reactions of the free radicals involved in the reaction. It is suggested that the minor product propane arises mainly from a hydrogen abstraction by 1-propyl from hexane with a contribution from a minor termination process involving ethyl and methyl.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550190202
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