Reactions of CF3 radicals with aromatics. Part 4.—Hydrogen abstraction from benzene at high temperatures and the bond dissociation energy D(C6H5—H)
- 1 January 1971
- journal article
- Published by Royal Society of Chemistry (RSC) in Transactions of the Faraday Society
- Vol. 67, 2077-2084
- https://doi.org/10.1039/tf9716702077
Abstract
The reactions of CF3 radicals with benzene in the range 100–400°C were studied using the photolysis of hexafluoroacetone as a source of radicals. The addition of CF3 radicals to the benzene ring becomes reversible above 140°C. Below 140°C, pesudo H-abstraction occurs via the reactions CF3+ C6H6→CF3C6H6, CF3+ CF3C6H6→CF3H + C6H5CF3, but at higher temperatures, genuine H-abstraction by reaction (3) occurs CF3+ C6H6→CF3H + C6H5(3), and we obtain log k3(cm3 mol–1 s–1)=(11.31±0.28)–(9110±760)/θ, where θ= 2.303 RT cal mol–1. Combination of E3 and published data on E–3, (for the reverse of reaction (3)), gives ΔH° 3 from which ΔH° f(C6H5)= 77.9±2.0, D(C6H5–H)= 110.2±2.0 kcal mol–1, both at 298 K. These values are compared with published data and the following are recommended: ΔH° f(C6H5)= 77.7±2.0 and D(C6H5—H)= 110.0±2.0, both in kcal mol–1.Keywords
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