ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
H2S increases the thermal isomerization of butene-2 cis (Bc) to butene-1 (B1) and butene-2 trans (Bt) around 500°C. This effect is interpreted on the basis of a free radical mechanism in which buten-2-yl and thiyl free radicals are the main chain carriers. B1 formation is essentially explainedby the metathetical steps: whereas the free radical part of Bt formation results from the addition-elimination processes:. It is shown that the initiation step of pure Bc thermal reaction is essentially unimolecular: and that a new initiation step occurs in the presence of H2S:. The rate constant ratio has been evaluated: \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{k_2 }}{{k_3 }} \simeq 0.4\exp ^{ - (6500 \pm 1000)/RT} (RT\,in\,cal/mol) $$\end{document} and the best values of k1 and k1', consistent with this work and with thermochemical data, are \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 \simeq 10^{15.5 - 85,500/2.3RT} \sec ^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{1^\prime } \simeq 10^{13.6 - 53,700/2.3RT} {\rm cm}^3 /{\rm mol}\,{\rm sec} $$\end{document}. From thermochemical data of the literature and an “intrinsic value” of E-3 ⋍ 2 kcal/mol given by Benson, further values of rate constants may be proposed: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 \simeq 10^{14 - 9,300/2.3RT} cm^3 /mol\sec $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 \simeq 10^{13.6 - 15,800/2.3RT} cm^3 /mol\sec $$\end{document} is shown to be E4 ⋍ 3.5 ± 2 kcal/mol, of the same order as the activation energy of the corresponding metathetical step.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550121204
