Study of n-butane pyrolysis at high temperature in a flow system allows measurement of the sum of the rate constants of the initiation reactions
(2)
and of the Arrhenius parameters of the reactions
Established data for kl/k2 allow estimation of kl for 951'K and this, with recent thermochemical data, yields the result log k-1 &mole s-l) = 8.5, in remarkable agreement with a recent measurement [20] but over sixty times smaller than conventional assumption. The product k3k4 (1.2mole-2s-2) is found to be associated with the Arrhenius parameters log (A3A4) = 21.90 f 0.6 and (Es + Ed) = 38.3 f 2.7 kcal/mole. These values are much higher than would be expected on the basis of low temperature estimates. Independent evaluation gives log A4 = 10.5 Z!Z 0.4 (Lmole-ls-l) and E4 = 20.1 f 1.7 kcal/mole, hence log A 3 = 11.4 f 0.8 (1.mole-ls-') and E3 = 18.2 f 3.2 kcal/mole. These values are shown to be entirely consistent with a wide range of results from pyrolytic studies, and it is argued that they further confirm the view that Arrhenius plots for alkyl radical-alkane metathetical reactions are strongly curved, in part due to tunneling and, appreciably, to other as yet unidentified effects. Since there is published evidence that metathetical reactions involving hydrogen atoms show even greater curvature, it is suggested that this may be a characteristic of many metathetical reactions.