Quantum-chemical analysis of the disproportionation of nitroxyl and peroxyl radicals in oxidizing organic compounds

The enthalpy change of disproportionation reaction of nitroxyl and peroxyl radicals was calculated by the DFT B3LYP/cc-pVDZ method. The regeneration of the corresponding hydroxylamine during the oxidation of unsaturated compounds inhibited by nitroxyl radicals is shown to be associated with the disproportionation of the nitroxyl and peroxyl radicals.     

Features of Methyl Linoleate Oxidation in Triton X-100 Micellar Buffer Solutions

Russian Journal of Applied Chemistry - The kinetics of oxygen absorption during the oxidation of methyl linoleate in Triton X-100 micelles has been studied. The order of the reaction with respect...     

Substituted p‐hydroquinones as a chain‐breaking antioxidant during the oxidation of styrene

The technique based on monitoring oxygen consumption was applied to test 13 substituted p‐hydroquinones (QH₂) as a chain‐breaking antioxidant during the oxidation of styrene initiated by 2,2′‐azobis(2,4‐dimethylvaleronitrile) at 37°C. The methodology originally developed to test monophenolic antioxidants was modified to fit it to specific features of oxidative transformation of QH₂. Chain‐breaking capability of QH₂ was characterized by two parameters: the rate constant k₁ for reaction of QH₂ with the peroxy radical LO₂^·: (1) QH₂ + LO₂^· → QH^· + LOOH and the stoichiometric factor of inhibition, f, which shows how many kinetic chains may be terminated by one molecule of QH₂. Rate constants k₁ × 10⁵ (in M^?1 s^?1) were found to be 5.54 (nonsubstituted QH₂); 7.13 (Me‐QH₂); 13.1 (Et‐QH₂); 12.0 (t‐Bu‐QH₂); 15.6 (2,6‐Me₂‐QH₂); 18.8 (2,3‐Me₂‐QH₂); 17.1 (2,5‐Me₂‐QH₂); 13.7 (2,6‐(MeO)₂‐QH₂); 4.70 (2,6‐Ph₂‐QH₂); 0.90 (2,5‐Cl₂‐QH₂); 23.2 (Me₃‐QH₂); 4.40 (2,3‐(MeO)₂‐5‐Me‐QH₂). Parameter f never exceeds 2; for the majority of QH₂, f was found to be visibly less than 2, decreasing when the rate of initiation decreased. Both experimental data and results of computer kinetic simulations suggest that, contrary to monophenolic antioxidants, the main path of QH^· transformation is the self‐disproportionation rather than recombination of QH^· with LO₂^·. Most likely, f is commonly lower than 2 because of the reaction of QH^· with molecular oxygen. The latter may result in faster depletion of QH₂ and the increase in the rate of inhibited oxidation. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 162–171, 2002; DOI 10.1002/kin.10041