ABSTRACT:The technique based on monitoring oxygen consumption was applied to test 13 substituted p-hydroquinones (QH 2 ) 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 QH 2 . Chain-breaking capability of QH 2 was characterized by two parameters: the rate constant k 1 for reaction of QH 2 with the peroxy radical LO 2 · : (1) QH 2 + LO 2 · → QH · + LOOH and the stoichiometric factor of inhibition, f , which shows how many kinetic chains may be terminated by one molecule of QH 2 . Rate constants k 1 × 10 5 (in M −1 s −1 ) were found to be 5.54 (nonsubstituted QH 2 ); 7.13 (Me-QH 2 ); 13.1 (Et-QH 2 ); 12.0 (tBu-QH 2 ); 15.6 (2,6-Me 2 -QH 2 ); 18.8 (2,3-Me 2 -QH 2 ); 17.1 (2,5-Me 2 -QH 2 ); 13.7 (2,6-(MeO) 2 -QH 2 ); 4.70 (2,6-Ph 2 -QH 2 ); 0.90 (2,5-Cl 2 -QH 2 ); 23.2 (Me 3 -QH 2 ); 4.40 (2,3-(MeO) 2 -5-Me-QH 2 ). Parameter f never exceeds 2; for the majority of QH 2 , 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 LO 2 · . 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 QH 2 and the increase in the rate of inhibited oxidation.

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The history and development of free radical chemistry and its derivatives in Russia and other countries are presented here. Scienti c work from Lavoisier and Gomberg to modern scientists is discussed. Many edifying and amusing moments in free radical chemistry are recalled in this review. A small excursion is made into the concept of radical stability. Numerous gures show that the chemical structures of free radicals are among the many beautiful aspects of modern organic chemistry. The review of the Russian grey literature on free radicals is of peculiar interest. The problems of priorities in free radicals have been studied. The exceptional perspectives of free radical chemistry are shown.

The results of experiments and computer simulations on the radical chain oxidation of methyl linoleate in micelles are reported. The reaction rate constants included in the developed mathematical model are estimated. The ratio of the rates of first order and bimolecular chain termination is examined. It is dem onstrated that the rate constant of bimolecular chain termination in micelles is lower than that in the homo geneous phase.

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