42473-26-7Relevant academic research and scientific papers
The chain-breaking antioxidant activity of phenolic compounds with different numbers of O-H groups as determined during the oxidation of styrene
Tikhonov, Ivan,Roginsky, Vitaly,Pliss, Evgeny
experimental part, p. 92 - 100 (2009/06/28)
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 k1 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 k1 × 105 (in M-1 s-1) were found to be 10 (catechol), 27 (pyrogallol), 34 (3,6-di-tert-Bucatechol), 4.3 (protocatechic acid), 12 (gallic acid), 15 (caffeic acid), 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 k1 with the structure of PP and the O-H bond dissociation enthalpy has been discussed.
ESR study of the effect of water on the kinetics of proton transfer and exchange in solutions of semiquinone radicals
Masalimov, A. S.,Bazhikov, K. T.,Melbardis, L. E.,Prokof'ev, A. I.
, p. 953 - 956 (2007/10/02)
The interaction of 3,6-di-tert-butyl-2-hydroxyphenoxyl with triethylamine in the reaction of proton transfer is catalyzed by water.However, the rate of proton exchange with diethylamine is independent of water admixtures in the reaction medium.ESR showed that the complexing of 3,6-di-tert-butyl-2-hydroxyphenoxyl with water leads to redistribution of the spin density. - Key words: 3,6-di-tert-butyl-2-hydroxyphenoxyl; triethylamine; diethylamine; complexing; ESR.
ESR ANALYSIS OF THE KINETIC ALKALINITY OF PSEUDOEPHEDRINE
Masalimov, A. S.,Nikol'skii, S. N.,Abdykarimova, A. P.,Prokof'ev, A. I.,Muldakhmetov, Z. M.
, p. 1559 - 1562 (2007/10/02)
The kinetics of protonation of pseudoephedrine by 3,6-di-tert-butyl-2-hydroxyphenoxyl have been analyzed by the ESR technique.It was shown that protolysis of the radical produced closed ionic pairs with the pseudoephedrine cation in a dimer state. Keywords: ESR, pseudoephedrine, 3,6-di-tert-butyl-2-hydroxyphenoxyl, ion pairs.
Intramolecular Hydrogen-Exchange in o-Quinone Radicals
Beinhoelzl, R.,Grampp, G.,Jaenicke, W.
, p. 169 - 182 (2007/10/02)
In some substituted o-quinone-radicals the exchange of cations between the oxygen atoms is investigated by means of alternating ESR-line broadening.No effect is found with cations like K(+), Li(+), AlCl2(+), LaCl2(+).However, H and D are exchanged in 3,6-di-tert-butyl-o-semiquinone (as was found by Prokof'ev et al.).The rate constants and activation parameters of the reaction are measured in 10 solvents.The results are discussed in terms of inner (λi) and outer (λo) reorganization energies.Both could be evaluated experimentally: λi(H) = 42 kJ mol-1; λi(D) = 69 kJ mol-1, λo = 59*γ kJ mol-1 (0.02 2 - 1/εs with n = refractive index, and εs = static dielectric constant).In etheric solvents an additional activation energy was found which was ascribed to an O...H bond.With two models of the solvent reorganization, due to Marcus and to Kirkwood the same charge transfer of 0.3 e0 between the O atoms was found during the H motion (e0 = elementary charge). - Keywords: o-Quinone radicals / Hydrogen exchange / Kinetics
