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Volume 64, 1968
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Bromination of fluoroalkanes. Part 4.—Kinetics of thermal bromination of fluoroform and pentafluoroethane

Abstract

The thermal brominations of CF3H and C2F5H have been studied in the ranges 361–431° and 323–458°C respectively. The kinetics agree with the reactions [graphic omitted] From measurements of initial rates, log k3(cm3 mole–1 sec–1)=(13.107 ± 0.035)–(22,320 ± 110)/2.303 RT, log k4(cm3 mole–1 sec–1)=(13.026 ± 0.020)–(19,305 ± 61)/2.303 RT. The inhibition by added HBr was studied with both systems. For Br2+ CF3H, the values of k–3/k9 obtained agree with previous independent data, the combined result being, log (k–3/k9)=(–0.58 ± 0.04)–(2,130 ± 90)/2.303 RT. For the system Br2+ C2F5H, log (k–4/k15)=(–0.45 ± 0.06)–(2,750 ± 250)/2.303 RT. The data for reactions (3) and (4) are combined with previous competitive results to give for the reference reactions, Br + CH4→ HBr + CH3, Br + CH3Br → HBr + CH2Br, log kCH4(cm3 mole–1 sec–1)=(13.991 ± 0.049)–(18,580 ± 140)/2.303 RT, log kCH3Br(cm3 mole–1 sec–1)=(14.000 ± 0.058)–(16,310 ± 170)/2.303 RT. Arrhenius parameters are tabulated for all bromination reactions studied to date.

From Arrhenius parameters for bromination reactions, the following bond dissociation energies are obtained: D(CF3—H)= 106.7 ± 0.5, D(C2F5—H)= 102.6 ± 1.2 and D(CH3—H)= 104.3 ± 0.7, all in kcal mole–1 at 298°K. These figures are compared with results from other sources and recommended values of the three quantities are, D(CF3—H)= 106.4 ± 0.5, D(C2F5—H)= 102.9 ± 1.0 and D(CH3—H)= 104.2 ± 0.5 kcal mole–1.

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Article type: Paper
DOI: 10.1039/TF9686402130
Trans. Faraday Soc., 1968,64, 2130-2142

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    Bromination of fluoroalkanes. Part 4.—Kinetics of thermal bromination of fluoroform and pentafluoroethane

    J. C. Amphlett and E. Whittle, Trans. Faraday Soc., 1968, 64, 2130
    DOI: 10.1039/TF9686402130

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