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Notes: Experiments with propane-ethylene mixtures in the temperature range 760-830 K resulted in refinement of the role of ethylene inhibition in the decomposition of propane. The source of the rate-reducing effect of ethylene is the reaction This replaces the decomposition chains more slowly by means of the reactions than H-atoms do by direct H-abstraction from propane. Analysis of the ratios of the product formation rates showed that the selectivity of the ethyl radical for the abstraction of hydrogen of different bond strengths from propane was practically the same as that of the H-atom. The ratio of the rate constants of hydrogen addition to ethylene and methyl-hydrogen abstraction from propane by the H-atom (3) was determined \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{k_3 }}{{k_8 }} = 10^{5.89 \pm 0.05} \exp ( - 30.8 \pm 1.1{\rm kJ mol}^{{\rm - 1}} /RT) $$\end{document} as was that of the decomposition and the similar H-abstraction of the ethyl radical \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{k_3 }}{{k_8 }} = 10^{5.11 \pm 0.61} \exp ( - 129 \pm 10{\rm kJ mol}^{{\rm - 1}} /RT){\rm mol}^{{\rm - 1}} {\rm dm}^{\rm 3}. $$\end{document}Interpretation of the influence of ethylene required the completion of the mechanism with further initiation of the reaction besides termination via ethyl radicals.

Notes: On the basis of the thermal decomposition of mixtures of propylene and propane with molar ratios of 0.0-0.33 in the temperature range 779-812K, the influencing functions describing the inhibition by propylene of the decomposition of propane were determined. The rate-reducing effect is explained mainly by the reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 6} + {}^.{\rm R} \longrightarrow {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 5} + RH $$\end{document} (in which .R = .H, .CH3 and 2-Ċ3H7) and also by the addition reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 6} + {}^.{\rm H} \to 1 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \to 2 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7}. $$\end{document} It was established that the bulk of the allyl radicals formed \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 8} + {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 5} \to 1 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \to 2 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} $$\end{document} participate in the chain step, but, due to their lower reactivity, they restore the decomposition chain more slowly than the original radicals do.From the characteristic change in the ratio υCH4/υH2, the rate ratios of hydrogenabstraction reaction by radicals from propylene and propane could be determined. In these reactions there was no significant difference between the selectivities of the radicals. For an interpretation of the changes, the decomposition mechanism must be completed with the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 6} + 2 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} \to 1 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} + {\rm C}_{\rm 3} {\rm H}_{\rm 6}. $$\end{document}Evaluation of the influencing curves revealed that the initiation reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 6} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} \to {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 5} + {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 7} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 8} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} \to {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 7} + {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 7} $$\end{document} must be taken into account.By parameter estimation we have determined the rate ratios characterizing the above initiation reactions, the unimolecular decomposition of propane, hydrogen abstraction by radicals from propane and propylene, intermolecular isomerization of the 2-propyl radical via propane and propylene, and abstraction of propane hydrogens by the ethyl and methyl radicals; these are given in Tables II.

Notes: The thermal decomposition of azoethane (AE) was studied by detailed product analysis in the temperature and pressure intervals 508-598 K and 2.7-13.3 kPa. Besides the hydrocarbon products, three characteristic and quantitatively important nitrogen-containing compounds were also determined: ethyl-2-butyldiimide, ethanal-diethylhydrazone, and tetraethyl-hydrazine. Apart from the predominant termination reactions of the ethyl radical with itself and with the μ2 radical, the decomposition is characterized by a very short chain reaction. The measurements led to determination of the following rate constants and rate constant ratios:\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{rcl} {\rm log}(k_1 /S^{ - 1} ) &=& (16.0 \pm 0.2) - (207.6 \pm 2.0){\rm kJ mol}^{ - 1} /2.3RT\\ log(k_4 /k_3^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} s^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (3.3 \pm 0.1) - (54.3 \pm 1.3){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_5 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (3.0 \pm 0.1) - (33.7 \pm 1.4){\rm kJ mol}^{ - 1} /2.3RT \\ k_{11} /k_{12} &=& 1.3 \pm 0.1 \end{array} $$\end{document} for the following reactions:

Notes: The thermal decomposition of azoisopropane (AIP) was studied by detailed product analysis in the temperature and pressure intervals 498-563 K and 0.67-5.33 kPa. Besides the predominant termination and hydrogen-abstraction reaction of the 2-propyl radical, the decomposition is characterized by a very short chain process. The following rate constants were determined from the measurements\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{rcl} \log (k_1 {\rm /s}^{ - 1} ) &=& (16.3 \pm 0.2) - (199.9 \pm 1.6){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_4 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (4.1 \pm 0.3) - (52.5 \pm 3.0){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_5 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (2.4 \pm 0.1) - (27.6 \pm 1.3){\rm kJ mol}^{ - 1} /2.3RT \\ k_2 /k_3 &=& 0.51 \pm 0.02 \end{array}$$\end{document} for the following reactions:

Notes: The thermal decomposition of azoisopropane (AIP) was studied in the presence of various quantities of propylene in the temperature and pressure intervals 498-553 K and 3.33-5.33 kPa. The inhibition functions relating to formation of the products were determined; these proved a good basis for interpretation of the formation of the secondary decompositon products of AIP. The experimental data support the conception that the βμ radical - radical reactionoccurs. The product of this is not stable; its decomposition is one of the sources of the secondary products. The ratio of the rate constants was determined for the following reactions:

Notes: The thermal decompositions of azoethane and azoisopropane were studied in a large excess of ethylene in the temperature interval of 523-623 K. It was demonstrated that under such conditions, the bulk of the alkyl radicals react with ethylene. Via measurements on the consumption of the azo compound and on the formation of gaseous nitrogen, it was possible to determine the rate coefficients of the initiation reactions:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm R - N} = {\rm N - R} \to {\rm N}_{\rm 2} {\rm + 2R}^{\rm .} $$\end{document}. The resulting data were as follows: For azoethane, \documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_1 (\sec ^{ - 1}) = (15.8 \pm 0.1) - (205.1 \pm 1.5){\rm kJ/mol/2}{\rm .3RT} $$\end{document}. For azoisopropane, \documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_1 (\sec ^{ - 1}) = (16.2 \pm 0.3) - (196.8 \pm 2.6){\rm kJ/mol/2}{\rm .3RT} $$\end{document}

Notes: A study was made of the oligomerization of ethylene, initiated by the thermal decomposition of azoethane and azo-isopropane at low temperatures, where the polymerization equilibria are shifted somewhat in the direction of the formation of products with longer carbon chains. The findings supported the picture acquired from a study of the propionaldehyde-ethylene system. Also under these conditions the oligomerization proceeds via addition between the ethylene and radicals, followed by isomerization and decomposition of the longer radicals, with a tendency to yield propylene and longer olefins. At the lower temperatures the decomposition of radicals with shorter carbon chain becomes less important in comparison with their addition reactions and, in spite of the otherwise identical mechanism, this leads to a different product distribution.