O. T. Kasaikina

Hydrocarbon and lipid oxidation in micro heterogeneous systems formed by surfactants or nanodispersed Al2O3, SiO2 and TiO2

Abstract The effect of surfactants and micro dispersed solid oxides on the kinetics and mechanism of hydrocarbon (ethylbenzene, limonene, β-carotene) and lipid (sunflower oil triacylglycerols) liquid phase oxidation by molecular oxygen have been studied. Ionic surfactants sodium dodecylsulphate (SDS) and cetyltrimetyl ammonium bromide (CTAB) were found to affect the rate and mechanism of hydroperoxide decay and consequently the rate of the ethylbenzene and limonene oxidation. In the case of β-carotene, which does not form hydroperoxides in the course of oxidation; the surfactants do not affect the β-carotene consumption rate. Anionic surfactant SDS is found to be a catalyst for the heterolytic decay of hydroperoxides. In the case of α-phenyl ethyl hydroperoxide, the decay reaction catalyzed by SDS yields phenol that is an acceptor of free radicals. So the ethylbenzene oxidation is completely inhibited in the presence of SDS. The same effect on the ethylbenzene oxidation and its hydroperoxide decay was found to be caused by nanodispersed Al 2 O 3 . Cationic surfactant CTAB as a catalyst causes the decomposition of ethylbenzene and limonene hydroperoxides via free radical formation that results in acceleration of hydrocarbon oxidation. Solid oxides SiO 2 , TiO 2 non-ionic ethoxylated hydrocarbons, and sodium bis (2-ethylhexyl)sulfosuccinate (AOT) show a slight effect on the hydroperoxide decay and hydrocarbon oxidation rates. The effect of surfactants and cosurfactants on the inhibited oxidation of lipid and hydrocarbons is strongly dependent on the nature of antioxidant and surfactant used.

Effects of chain transfer and recombination/disproportionation of inhibitor radicals on inhibited oxidation of lipids

The kinetics of inhibited oxidation of lipids was studied by computer simulation to evaluate the contributions of the recombination/disproportionation of inhibitor radicals and chain transfer to retardation effects. The influence of inhibitor regeneration on the induction periods and inhibited oxidation rate was demonstrated.

Antioxidant Activity Evaluation Assay Based on Peroxide Radicals Generation and Potentiometric Measurement

A new version of potentiometric evaluation of antioxidant activity in biological liquids, food, drinks, and so forth, based on the mediator system combined with the free radicals generation has been proposed. A radical initiator, 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH), and K3[Fe(CN)6]/K4[Fe(CN)6] as a mediator system were used. Interactions of the mediator system with radicals, radicals with antioxidants, and erythrocytes have been investigated. The correlation coefficient between the data obtained in the presence and the absence of AAPH equals 0.98. In addition, the possibility to determine a free radical generation rate by using the mediator system has been demonstrated.

The inhibitory activity of natural phenolic antioxidants in the oxidation of lipid substrates

The suppression of the oxidation of triglyceride and methyl esters of lard and olive and sunflower oils by additives of natural phenolic acids (hydroxy and methoxy derivatives ofpara-hydroxybenzoic and cinnamic acids) at 100 °C was studied. The rate constants of the interaction of these acids with peroxyl radicals in the oxidation of cumene at 60 °C were determined by the chemiluminescence method. Caffeic acid is the most efficient lipid antioxidant, exceeding ionol and α-tocopherol.

Kinetic characteristics of initiated oxidation of limonene

The kinetics of oxygen absorption .n the process of limonen (4-isopropenyl- l-methulcyclohex-1-ene) oxidation was studied in chlorobenzene solution at 40–80 °C. The values of the kinetic parameters of oxidation and the activation energy (38.1 kJ mol−1) have been determined. The nonlinear dependence of the rate of the oxidation of limonene on its concentration has been established, The rate constants of the chain termination reactions were estimated by chemiluminescence techniques.

Oxidative treatment of biomass using catalysts based on iron( iii ) oxides

The catalyst based on iron(iii) oxides was prepared by hydrolising FeIII salt in water and adding surfactants. The catalyst is active in decomposing H2O2 and accelerates the oxidative destruction of ligno-containing biomass at atmospheric pressure and moderate temperatures of 60–70 °C under the action of H2O2 and O2. The particle size in the initial catalyst is several nanometers. The catalyst activity in decomposition of H2O2 changes nonlinearly and non-monotonically with increasing initial brutto-concentration of the FeIII ions. The catalyst obtained under the optimal conditions decomposes H2O2 as fast as the most active relevant systems do. As the result of thermal-oxidative destruction the biomass (sawdust, peat, olive pulp, straw) is transformed to the low-molecular products of oxidation of lignine, cellulose, lipoproteides, and sugars; the solid residue is represented by cellulose and its derivatives. The yield of solid residue depends on the biomass nature, concentration ratios of the reagents (biomass, catalyst, hydrogen peroxide), and the duration of destruction. On the basis of the data on the rate of peroxide consumption, evolution and transformation of catalyst, and concentration dependences the conclusion was made, that the nanocatalyst based on iron(iii) oxides combined with H2O2 and O2 forms the catalytic system for oxidative destruction of ligno-containing biomass, activity of which depends on the type of organic raw materials and oxidizer.

Kinetics of limonene autooxidation

The kinetic parameters of the oxidizability of Iimonene,kp/(2kt)0.5 = 6.0- 10−3 L0 5 mol−5 s−0.5, and of the bimolecular radical decomposition of hydroperoxides 2ekd = 6.0 · 10−6 L mol−1 s−1 were determined at 60 °C The oxidation rate increases in the presence of micro additives of water. Average effective diameters of particles formed in the water-AOT-(n-decane + lirnonene) microemulsion were measured by the light scattering technique. The hydroperoxides were found to affect the size of the microemulsion particles.

Effect of the conditions of liquid-phase oxidation of unsaturated compounds on the behavior of hydroquinoline antioxidants

The inhibition activity of hydroxy-and alkoxysubstituted 2,2,4-trimethyl-1,2,3,4-tetrahydroquinolines (HQs) was studied in R(+) limonene autooxidation and oxidation catalyzed by cationic surfactants and transition metal compounds. It was shown that HQs exhibit a high antioxidant activity in limonene autooxidation. In oxidation catalyzed by cationic surfactants and Fe(III), Co(II), or Mn(II) acetylacetonates, HQs also show a relatively high antioxidant activity and, additionally, react with hydroperoxides along with the reactions with peroxyl radicals in the presence of these catalysts. In the presence of Cu(II) compounds, HQs significantly accelerate the oxidation. It was found that HQs form complexes with Cu(II), which catalyze hydroperoxide degradation into free radicals.

Interaction between hydrogen peroxide and cobalt(II) acetylacetonate in the system of reverse micelles of triton X-100 nonionic surfactant in cyclohexane

The yield of free radicals upon the decomposition of hydrogen peroxide catalyzed by cobalt acetylacetonate (Co(acac)2) in the systems of reverse micelles of TX-100/n-hexanol and AOT in cyclohexane at 37°C was studied with the inhibitor method using a stable nitroxyl radical as a spin trap. It is shown that, in micellar AOT solutions in cyclohexane as well as in n-decane, H2O2 and Co(acac)2 in practice do not react, because H2O2 is localized in a micelle water pool and Co(acac)2, in the organic phase. Therefore, the generation of radicals is not observed in AOT solutions in cyclohexane, whereas, in aqueous solution, Co(acac)2 catalyzes the radical decomposition of H2O2. In the system of mixed reverse micelles of TX-100 and n-hexanol in cyclohexane, at equal overall concentrations of H2O2 and Co(acac)2, the rate of radical formation is much higher than in aqueous solution; i.e., the micellar catalysis of the radical decomposition of H2O2 takes place. It follows from measurements of UV and ESR spectra and the kinetics of changes in the content of peroxides in the reaction mixture that TX-100 and n-hexanol react with free radicals formed upon H2O2 decomposition and with atmospheric oxygen.

Temperature effect on the rate of formation of free radicals in CTAB-catalyzed decomposition of hydroperoxides

The temperature effect on the rate of the decomposition of hydroperoxides and the rate of the formation of free radicals in the oxidation of ethylbenzene with molecular oxygen in the presence of α-phenylethyl hydroperoxide—cetyltrimethylammonium bromide (CTAB) as a catalytic system for free radical generation was studied by kinetic methods (from the oxygen consumption and hydroperoxide decomposition rates) and the inhibition method involving different acceptors of free radicals.