Bond dissociation energies from equilibrium studies. Part 3.—D(CF3—Cl), D(C2F5—Cl) and the enthalpy of formation of CF3Cl

Abstract

The gas-phase equilibria, Cl₂+CF₃Br⇌BrCl+CF₃Cl (3) Br₂+CF₃Cl⇌BrCl+CF₃Br (4) Cl₂+C₂F₅⇌BrBrCl+C₂F₅Cl (5) have been studied over the temperature ranges: 559–749°C, (3); 556–661°C, (4); 465–560°C, (5). From the measured K_p, we obtain, ΔH^°₃=–10.69±0.15, ΔH^°₄= 10.49±0.20 and ΔH^°₅=–10.3±0.6 kcal mole^–1, all at 298°K. These enthalpy changes are combined with other data to give D(CF₃–Cl)= 86.1±0.8, D(C₂F₅–Cl)= 82.7±1.7 and ΔH^°_f(CF₃Cl)=–169.4±1.0, all in kcal mole^–1 at 298°K. These results are compared with other published values of D(CF₃–Cl) and ΔH^°_f(CF₃Cl). A comparison of bond dissociation energies of the type D(CF₃–X) from studies of equilibria with those obtained by electron-impact methods favours the “low” value of I(CF⁺₃)= 9.35–9.50 eV rather than the “high” value of 10.15 eV, all three value having previously been proposed. Bond dissociation energies in simple organic fluorine compounds are compared with those for corresponding compounds in which fluorine is replaced by hydrogen.