Thermal decomposition of dicyclohexylperoxydicarbonate in different types of solvents

We have obtained data on the rates of homolysis and induced decomposition of dicyclohexylperoxydicarbonate (PC) in different types of solvents: n-decane, cyclohexane, chlorobenzene, acetonitrile. The rate of induced decomposition is determined by the activity of the radicals formed from the solvent. We have established that benzene and chlorobenzene participate in radical reactions of induced decomposition of PC, which leads to formation of a number of isomeric aryl-containing compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 48–55, January, 1991.We thank A. B. Gagarina for participation in discussion of the results.     

Effect of surfactants on liquid-phase oxidation of hydrocarbons and lipids

A review is presented compiling new data on liquid-phase oxidation of hydrocarbons and plant oils in microheterogeneous environment formed by the addition of surfactants. Cationic surfactants catalyze the decomposition of the primary oxidation products, hydroperoxides, into free radicals thus accelerating the oxidation process. Anionic surfactants catalyze the heterolystic decomposition of hydroperoxides and therefore are excellent antioxidants for ethylbenzene, cumene, and other alkylaromatic hydrocarbons.     

Oxidation of nonionic surfactants with molecular oxygen

Kinetic regularities are studied for the air oxidation of surfactants that are widely used in the food industry, such as natural phosphatidylcholine (egg lecithin, PC) and synthetic nonionic surfactants Triton X-100 (ТХ-100), Tween 65, and Pluronic F68. Azobis(amidinopropane)-dichloride-initiated oxidation of these surfactants in an aqueous medium at 37°C develops via the chain free-radical mechanism. The chain length is equal to 5–10 units, depending on the initiator-to-surfactant concentration ratio. The rate of surfactant oxidation in an aqueous medium is proportional to the rate of radical initiation. At the same mass concentrations of the reagents, the rate of PC oxidation is several times higher than the oxidation rates of the other surfactants. The addition of TX-100 to PC liposomes decelerates the oxidation; i.e., TX-100 plays the role of an antioxidant for PC. The superposition of the oxidation rates of individual and mixed PC and TX-100 with the sizes of the microaggregates formed in their aqueous solutions shows that the antioxidation action of TX-100 is realized via the formation of a protective layer composed of its ethylene oxide groups, which shields PC liposomes from radicals, which are initiated in the bulk of an aqueous phase due to the decomposition of azobis(amidinopropane) dichloride.     

Effect of phosphate buffer solutions on the reactions of glutathione with hydrogen peroxide and peroxyl radicals

Differences in the kinetics and mechanism of the reaction of glutathione (GSH) with hydrogen peroxide (H₂O₂) in deionized water and in phosphate buffer systems with pH ≥ 7 frequently used in biochemical studies were revealed. The formation of GSH dimers and complexes with H₂O₂ in water plays a substantial role in the kinetics of the process, which is manifested as nonlinear dependences of the rate of GSH consumption (W_GSH) and the rate of radical formation (W_i) on the reagent concentrations. In phosphate buffer solutions (PBS), the oxidation of GSH by air oxygen is enhanced and the radical formation rate decreases sharply. An effect of NaCl and KCl in PBS on W_GSH and W_i was observed, unlike a sodium—potassium phosphate buffer mixture (PB). Under other equivalent conditions, W_GSH PBS is several times lower and W_i is higher than those in PB containing no chlorides. It was found that the rate of the thiol-ene reaction of unsaturated phenol resveratrol (RVT) with GSH initiated by the radicals formed in the presence of H₂O₂ in PBS is nearly three times lower than that in water, whereas in PB resveratrol is not consumed under the same conditions. However, in the reactions with peroxyl radicals formed upon the decomposition of 2,2′-azobis(2-methylpropionamidine) dihydrochloride the GSH consumption rate is the same in both phosphate buffer systems.

     

Effect of sulfur-containing phenols and amines on the decomposition of hydroperoxides

The effect of polyphenol sulfides (PPS) and dithiolthione, the sulfur-containing derivative of acetone anil, on the decomposition of cumyl andn-decyl hydroperoxides (DHP) studied. The decomposition of cumyl hydroperoxide (CHP) in the presence of PPS is a complex multistep autocatalytic process during which an efficient catalyst for CHP decomposition is formed from the initial PPS. The PPS catalyst for CHP decomposition is deactivated in the reaction with peroxy radicals. Kinetic characteristics of the reaction between polyphenol sulfides and CHP are determined. Dithiolthione catalytically decomposes CHP and reacts with n-decyl hydroperoxide DHP in the stoichiometric ratio     

Kinetic description of the oxidation of hydrocarbons inhibited by sulfur-containing hydrogenated quinolines

The inhibiting effect of dithiolthione derivatives of hydrogenated quinolines (DTT) on the oxidation of various hydrocarbons (n-decane,n-decene, ethylbenzene, -carotene) was investigated. The inhibiting effect of the DTTs is greater at high temperatures (>100 °C) than that of the parent hydrogenated quinolines and weaker at moderate temperatures. The DTTs do not affect the decomposition of hydroperoxides. Probably, the introduction of a dithiolthione cycle to a hydroquinoline molecule decreases its reactivity toward O₂ and peroxide radicals, which favors the enhancement of the antioxidative activity of the DTTs at elevated temperatures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 814–818, May, 1994.     

A kinetic model for limonene oxidation

The kinetic regularities of the autooxidation of R(+)−limonene (LH) were experimentally studied at various temperatures. A kinetic model including the main elementary reactions and the corresponding rate constants was developed. The degenerate chain branching during limonene oxidation proceeds via bimolecular reactions and involves hydroperoxide LOOH + LH → L· + LO· + H₂O and LOOH + LOOH → LO· + LO₂ · + H₂O. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 80–86, January, 2008.