Mechanism of Formation and Decomposition of C6H5(O2•)C(OH)C6H4OH

Abstract

In the present theoretical study, the thermochemical properties of Ph(O₂^•)C(OH)PhOH and considered products of its oxidation are calculated using the DFT approaches (M062X, B3LYP, wB97XD, M08HX, MN15) at the 6−311++G(d, p) level of theory. The DFT values of Δ_raH^o(Y_i) of the atomization of considered structures are corrected using the linear calibration dependencies reported for the peroxides as well as for the hydrocarbons (including aromatic and simple oxygenated compounds). The values of Δ_fH^o(Y_i, CORR) ± 3SD_i, derived from the corrected values of Δ_raH^o(Y_i, CORR), are coordinated by the intersection of their 3SD_i intervals, determined previously. The values of Δ_fH^o(Y, MEAN) ± 2SD_Y of the Ph(O₂^•)C(OH)PhOH (2F), Ph^•─OO─C(OH)PhOH (3G), HOPh^•─OO─C(OH)Ph (2G), PhC(OH)₂PhOH (1H), Ph(O₂H)C(OH)PhOH (4G) and Ph(O^•)C(OH)PhOH (1G) (corresponded, respectively, to −159.4 ± 6,−55.2 ± 6,−61.5 ± 3.7,−385.8 ± 6,−293.4 ± 1.4,−148.9 ± 6 kJ/mol), as well as the values of E_a^‡ = 127.8 ± 7, 121.2 ± 8, 17.2 ± 5, 19.4 ± 3 kJ/mol, determined, respectively, for the reactions (R21a), (R21b), (R22a), (R22b) and the values of the rate constants of associated reactions, are reported for the first time. According to calculations, the replacement of >C^•H by OH group increases the values of dissociation energy (DE) of >C(X)─O₂^•, >C(X)O─O^•, >C(X)O─H, PhC(X)OO─^•PhOH, and HOPhC(X)OO─^•Ph bonds, but decreases those values of >C(X)O₂–H, HOPhC(X)^OO•Ph, and PhC(X)^OO•PhOH bonds. As a result of increased stability of the >C(X)─O₂^• bond (X = OH), the higher temperatures can be used for the chain production of p-PhC(O₂H)HPhOH and p-PhC(O₂H)(OH)PhOH at high concentrations of p-PhCH₂PhOH. On the contrary, the contribution of reactions (R21a) and (R21b) to the oxidation is significant under low concentrations of p-PhCH₂PhOH. Its also found that the stable intermediate O₂ π–π cluster, predicted for the >C^•(H) radical, is not observed for the reaction of >C^•(OH) with O₂, due to the formation of a hydrogen bond between the OH group and partially charged O₂^δ−.