A. I. Rusakov

The kinetics and mechanism of reactions of aliphatic stable nitroxyl radicals with alkyl and peroxide radicals during styrene oxidation

A kinetic study (EPR, microvolumometry), quantum-chemical analysis (DFT B3LYP/6-31G*), and kinetic simulation of the antioxidant activity of aliphatic stable nitroxyl radicals during styrene oxidation was performed. The key reactions constituting the detailed mechanism of the process were analyzed. It was shown that the inhibiting action of nitroxyl radicals was caused by their reaction not only with alkyl radicals but also with substrate peroxy radicals, which resulted in the regeneration of nitroxyl radicals in chain-termination steps.

Kinetic study and simulation of methyl linoleate oxidation in micelles

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 demonstrated that the rate constant of bimolecular chain termination in micelles is lower than that in the homogeneous phase.

Dimerization and protonation reactions of nitrosonitrobenzenes radical anions

The electrochemical behavior of 2-, 3-, and 4-nitrosonitrobenzenes (NNB) in DMF (with Bu4NClO4 suppoting salt) in the presence and in the absence of different proton donors (water, phenol, benzoic, acetic, chloroacetic, and sulfuric acids) is studied by the methods of cyclic voltammetry, chronoamperometry and also by electrolysis at the controlled potential. The electrochemical reduction of these compounds is shown to preferentially afford either monomeric (N-nitrophenylhydroxylamines) or dimeric (azoxy compounds) products, which is determined by the interplay between reactions of protonation and dimerization of NNB radical anions. The dimerization reactions proceed fast and reversibly to afford the corresponding dimeric dianions with the basicity much higher as compared with NNB radical anions as the result of which the monomeric products are formed in the presence of “strong” proton donors and the dimeric products form in the presence of “weak” proton donors. Like the effective rate of formation of dimeric products, the basicity of radical anions increases in the row 4- < 3- < 2-NNB.

Effect of microheterogeneity on the kinetics of oxidation of methyl linoleate in micelles

The kinetic results of the radical chain oxidation of methyl linoleate (LH) in micelles were given. The oxidation rate depends on the average number of substrate molecules in the micelle and is almost independent of the micelle concentration under the given conditions. The chain propagation and termination were assumed to predominantly occur inside the micelle. Possible reasons for linear chain termination during the oxidation of polyunsaturated fatty esters in microheterogeneous systems were discussed.

Kinetics and Mechanism of Reactions of Aliphatic Stable Nitroxide Radicals in Chemical and Biological Chain Processes

© 2012 Pliss et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Kinetics and Mechanism of Reactions of Aliphatic Stable Nitroxide Radicals in Chemical and Biological Chain Processes

EXPERIMENTAL STUDY OF DIMERIZATION OF RADICAL ANIONS OF AROMATIC CARBONYL COMPOUNDS

The rate constants of dimerization (k1) of radical anions of acetophenone, 1-acetylnaphthalene, 9-acetylanthracene, 9-formylanthracene, and anthracene in DMF containing 0.02 M tetrabutylammonium bromide were determined by differential cyclic voltammetry. It was shown that the values of k1 of the radical anions investigated are correlated with the values of the boundary electron density on the reaction sites, which in turn increase symbatically with an increase in the size of the aryl fragment or on incorporation of electron-acceptor functional groups in the anthracene nucleus.

Influence of the nature of solvent and substituents on the oxidation potential of 2,2,6,6-tetramethylpiperidine 1-oxyl derivatives

The influence of solvent (DMF, MeCN, and water) and R1, R2 substituent nature on the formal oxidation potential (E°´) of 4-R1,R2-2,2,6,6-tetramethylpiperidine 1-oxyls (1a—f) on a glass carbon electrode was studied by cyclic voltammetry. It was shown that for all the solvents the observed dependence had the form E°´ = ρ″σ″ + b, where σ″ is the substituent constant. The b values decreased with an increase of the solvent solvating ability, while the values ρ″ are similar for all the solvents, surpassing the corresponding values for nitroxyls of the imidazoline series with substituents at position 3, which can be interpreted as an abnormally strong influence of the substituent remote from the reaction center in 1a—f. The experimental values E°´ were linearly correlated with the reaction free energy values (ΔG) calculated by DFT B3LYP and MP2 for the gas phase contribution and by HF/PCM for the contribution of solvation effects. When applying the B3LYP and the HF/PCM approaches in combination, the dependence of E°´ on ΔG for all the considered solvents was described by a linear correlation equation with a slope close to unity and a constant term which was close to the theoretical value of the absolute potential of the reference electrode used.

Electroreduction mechanism of N-phenylhydroxylamines in aprotic solvents: formation of hydrogen bonds between N-(3-nitrophenyl)hydroxylamine and its radical anion

The electroreduction of N-(3-nitrophenyl)hydroxylamine in DMF was studied using cyclic voltammetry, chronoamperometry, and numerical simulation. It is shown that the stability of formed radical anion is significantly higher than that of the radical anion of the 4-nitrophenyl derivative. In the range of low concentrations and high potential scan rates, the electroreduction of N-(3-nitrophenyl)hydroxylamine is complicated only by the formation of complexes between the depolarizer molecules, most likely, due to hydrogen bonds, as well as between the depolarizer and its radical anion. The thermodynamic and kinetic parameters of these processes were evaluated.

Feasibility of a quantitative description of halide anion abstraction from aromatic radical-anions using quantum chemical reactivity indices

ConclusionsA quantum chemical reactivity has been proposed which permits the prediction of the rate constant of the halide anion from aromatic halide radical-anions in a rather broad range.

Prediction of the rate constants of the dimerization of radical-anions using PMO theory

ConclusionsThe absolute rate constants of the dimerization of radical-anions may be predicted in the framework of the PMO approach on the basis of data provided by the CNDO and INDO quantumchemical methods.