A reinvestigation of the deceptively simple reaction of toluene with OH, and the fate of the benzyl radical: a combined thermodynamic and kinetic study on the competition between OH-addition and H-abstraction reactions

Enthalpies of formation of the benzyloxyl, benzylperoxyl, hydroxyphenyl radicals and related species on the potential energy surface for the reaction of toluene with the hydroxyl radical

“…The reactions employed to obtain the enthalpy of formation of the benzyl radical are the following T + OH • → TR + H2O (12) T + CH3 • → TR + CH4 (13) Both are isodesmic reactions and we showed above that the theoretically calculated values obtained for H2O and CH4 employing these radicals are reasonably accurate. For both these reasons, one would expect to get good error cancellation and to obtain reasonable values of ∆ 298 .…”

“…Quantum mechanical calculations have been performed on radicals and closed shell species lying on the potential energy surface of the reaction of benzyl radical with O2, OH • , and H2O. These species arise in different channels in the reaction mechanism of toluene reaction with the OH • radical (see, for instance, Metcalfe et al [5], Murakami et al [10], Bounaceur et al [11] and ourselves [12,13]) and the enthalpies of formation were known for about half of the 17 compounds studied. Non-isodesmic reactions connecting products and reactants on these reaction paths, starting either from toluene or the benzyl radical, were used to calculate the enthalpies of formation.…”

“…Upper and lower limits of these average errors are approximated by twice the standard deviation (±2 Table 2. Enthalpies of reaction and formation, as well as error of the theoretical enthalpy of formation of TR calculated using reactions (12) and (13). All values are in kcal/mol.…”

“…The mechanisms studied in our work on the reaction between toluene and OH • are shown in Fig. 1 [12,13]. We framed there those species that are studied in this paper, in black for those with known experimental enthalpy of formation, and in red for the other ones.…”

“…A non-exhaustive list of recent studies can be found in references [5][6][7][8][9][10][11]. We have recently performed a detailed study of the possible routes for the reaction of toluene (T) with OH • , and further reactions of the intermediate radicals with both OH • and O2 [12,13]. Several intermediates were identified theoretically, for which scarce or no experimental information is available.…”