ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Studies of the reaction of Br + propylene to produce HBr and allyl radical were made using VLPR (Very Low Pressure Reactor) over the range 263-363 K. Apparent bimolecular rate constants k1app were found to vary in an inverse manner with the initial concentration of bromine atoms introduced into the reactor. Plots of k1app against [Br]0-1 give straight lines whose intercepts were taken to be the true bimolecular, metathesis rate constant k1. The reaction scheme is \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {\rm Br} + {\rm C}_{\rm 3} {\rm H}_6& \stackrel{1} {\rightleftharpoons}& {\rm HBr} + {\rm allyl}\\ {\rm Br} + {\rm allyl} & \stackrel{2} {\longrightarrow}& {\rm HBr} + {\rm allene}\\ \end{array} $$\end{document} where k2 ≫ k1 and k-1 [HBr] is negligibly small under our conditions.Arrhenius parameters for k1 were assigned for linear and bent transition states and shown to give excellent fits to the observed intercepts. \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm linear:}}\quad \log {(k_1 /{\rm cm}^3\, {\rm mol}^{{\rm - 1}}\,{\rm s}^{{\rm - 1}})} &=& 12.1 - 3.5/\theta\\ {{\rm bent:}}\quad \log {(k_1 /{\rm cm}^3\, {\rm mol}^{{\rm - 1}}\, {\rm s}^{{\rm - 1}})} &=& 12.7 - 4.4/\theta \end{array} $$\end{document} where θ = 2.303 RT (kcal mol-1).The dependence of k1app on [Br]0-1 is accounted for in terms of the reactivity of Br* (2P1/2) produced in the microwave discharge. The activation energy for the metathesis reaction of Br* with propylene is shown to be very small.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550200404
