The pyrolysis of benzoyl bromide and the determination of the relevant bond dissociation energies
Pyrolysis of benzoyl bromide in the presence of excess of toluene has been investigated. It has been shown that the rate-determining step is the unimolecular dissociation C 6 H 5 . CO. Br → C 6 H 5 . CO + Br, followed by the rapid decomposition of benzoyl radicals C 6 H 5 . CO → C 6 H 5 ⋅ + CO. Bromine atoms and phenyl radicals seem to be removed from the system by the reactions C 6 H 5 . CH 3 + Br → C 6 H 5 . CH 2 ⋅ + HBr and C 6 H 5 . CH 3 + Ph ⋅→ C 6 H 5 . CH 2 ⋅ + C 6 H 6 . The activation energy of the rate-determining dissociation process has been estimated using the least square method at 57⋅0 kcal/mole and has been identified with D (C 6 H 5 ⋅ CO-Br). Thus, having D (C 6 H 5 ⋅ CO-Br) = 57⋅0 kcal/mole, the heat of formation of benzoyl radicals has been calculated at ∆ H f (C 6 H 5 . CO) = 15⋅6 kcal/mole, and consequently the values for various bond dissociation energies of the type D (C 6 H 5 . CO- X ) have been derived.