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 Kp, 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.