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The chain‐breaking antioxidant activity of phenolic compounds with different numbers of O‐H groups as determined during the oxidation of styrene
Author(s) -
Tikhonov Ivan,
Roginsky Vitaly,
Pliss Evgeny
Publication year - 2009
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20377
Subject(s) - chemistry , pyrogallol , gallic acid , catechol , caffeic acid , styrene , reaction rate constant , organic chemistry , medicinal chemistry , antioxidant , quercetin , nuclear chemistry , kinetics , copolymer , physics , quantum mechanics , polymer
The technique based on monitoring oxygen consumption was applied to test 18 polyphenols (PP) and model phenolics as a chain‐breaking antioxidant during the oxidation of styrene initiated by 2,2′‐azobis(2,4‐dimethylvaleronitril) at 37°C. The chain‐breaking capability of PP was characterized by two parameters: the rate constant k 1 for the reaction of antioxidants with the peroxy radical produced from styrene and the stoichiometric coefficient of inhibition, f , which shows how many kinetic chains are terminated by one molecule of PP. Rate constants k 1 × 10 5 (in M −1 s −1 ) were found to be 10 (catechol), 27 (pyrogallol), 34 (3,6‐di‐tert‐Bu‐catechol), 4.3 (protocatechic acid), 12 (gallic acid), 15 (caffeic acid), <0.01 (chrysin), 1.3 (kaempferol), 19 (quercetin), 5.3 (baicalein), 16 (epicatechin), 32 (epigallocatechin), 9.0 (dihydroquercetin), 3.3 (resveratrol), and 16 (nordihydroguaiaretic acid). The value of k 1 increases when going from one to two and three adjacent O‐H groups in a benzene ring (catechol and pyrogallol derivatives, respectively). At the same time, two O‐H groups in metaposition in a A‐ring of flavonoids actually do not participate in the inhibition. For the majority of PP, f is near to 2 independent of the number of OH groups. The correlation of k 1 with the structure of PP and the OH bond dissociation enthalpy has been discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 92–100, 2009