The oxidation of sulphide in aqueous solutions

The purpose of this work was to study the catalytic effect of activated carbon particles 7.5 μm in diameter on the initial oxidation rate of bisulphide, with oxygen as oxidant, in an aqueous solution buffered at a pH of 9.7 and at temperatures of 48.5, 35 and 25 °C. Two reactors were used: a stirred gas—liquid contactor to determine the kinetics and a continuous flow reactor to demonstrate that a continuous process is possible.The liquid phase oxidation of sulphide was found to be much faster in the presence of activated carbon. Kinetic equations for the initial rate of reaction are given separately for homogeneous and heterogeneous oxidation.As activated carbon shows a strong catalytic activity, it can be of interest in the oxidation of sulphide in industrial and other waste waters at low temperatures.     

Gamma-radiation induced oxidation of p-hydroquinone in aqueous solutions

The products of γ-radiation induced oxidation of p-hydroquinone (H₂Q) solutions are p-quinone (Q), 2-hydroxybenzoquinone (2-Q-OH) and hydrogen peroxide (H₂O₂). The effects of dose, [O₂], [H₂Q], pH and different anions on yields have been investigated. Plots of G(Q) and G (H₂O₂) versus pH give titration type curves with pK of ～1.2 and 1.3, respectively. This pK was attributed to protonation of the HO₂ radical. The protonated form can oxidize H₂Q. The neutral form of this radical appears to react with the semiquinone radical (HQ) to form (2-Q-OH) or disproportionate to give H₂O₂. A reaction mechanism is proposed to account for the experimental observations.     

Gamma-radiation induced oxidation of p-hydroquinone in aqueous solutions

P-hydroquinone (H₂Q) has been gamma-irradiated in the presence of O₂ and different alcohols in acidic solutions. In the presence of tert-BuOH, the oxidation products were quinone(q), 2-hydroxybenzoquinone (2-Q-OH) and hydrogen peroxide (H₂O₂). In case of propan-2-ol, ethanol and methanol, the oxidation products were as above in addition to a carbonyl compound. A chain reaction was observed in case of propan-2-ol and this was inhibited by H₂Q. The dependence of G(Q) and G(H₂O₂) on pH is a titration-type curve and the species responsible for this curve is assumed to be the protonated and unprotonated alcohol peroxy radicals.     

Kinetics of lecithin oxidation in liposomal aqueous solutions

The peculiarities of egg phosphatidylcholine (lecithin) oxidation with molecular oxygen in aqueous media are investigated. Under the action of ultrasound, lecithin forms multilamellar liposomes or vesicles in aqueous solutions. Lecithin is oxidized through a chain free-radical mechanism. The nonlinear dependence of the rate of oxygen absorption on the substrate concentration and the imitation of the linear termination of the oxidation chain are observed. The study of the inhibited oxidation of phosphatidylcholine suggests that catecholamines, such as dopamine, noradrenalin, and adrenalin, are markedly more efficient antioxidants than quercetin and α-tocopherol. Phosphate buffer solution is shown to strongly influence the ways of adrenalin transformation in reactions with peroxyl radicals.     

Radiation-induced oxidation of ferrous iron in aqueous solutions

Summary An investigation was made of the dependence of the yield G in the oxidation of aqueous solutions of ferrous iron on various factors. The limits within which the enhanced-G effect is observed and the accuracy with which the effect can be measured were established.     

Mechanism of alkyl iodide reduction to alkanes in aqueous solutions of Na2PtCl4?NaI?HClO4

Platinum(II) catalyzes the reduction of alkyl iodides to alkanes according to a mechanism involving oxidative addition of RI to Pt(II), reduction of the product complex RPt(IV) to RPt(II) by iodide ions and protolysis of the latter particle.

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(II) , RI Pt^II, - RPt^IV RPt^II .

     

Lattice model for the wetting transition of alkanes on aqueous surfactant solutions

Droplets of alkanes on aqueous solutions of the cationic surfactants C(n)TAB (CH3(CH2)(n-1)N+ (CH3)3Br-) exhibit a first-order wetting transition as the concentration of the surfactant is increased. A theoretical model is presented in which the surface free energy is broken down into a long-range dispersion interaction and a short-range interaction described by a 2D lattice gas, taking into account the interaction between oil and surfactant molecules. The model provides quantitative agreement with the observed wetting transitions and the variation in composition of the wetting film with bulk surfactant concentration. The behavior of oil drops on large reservoirs of dilute surfactant is discussed.     

Substrate selectivity and mechanism of oxidation of alkanes by peroxynitrous acid in aqueous solution

The relative rate constants (k_rel) were measured for the oxidation of alkanes (RH) by peroxynitrous acid (HOONO) in aqueous solutions at 25 °C. The krel values for the reactions of RH with HOONO and with OH radicals in the series of C₂-C₇ alkanes and the isotopic effects (c-C₆H₁₂/c-C₆D₁₂) agree. However, the k_rel value for methane was lower than for its reaction with OH. Possible reaction mechanisms are discussed. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 295–299, September–October, 2006.     

Radiochemical oxidation of hydrazine in aqueous solutions containing oxygen

The chain mechanism of oxidation of hydrazine in aqueous solutions saturated with oxygen at pH > 7.5 was established. The yields of radiochemical decomposition of hydrazine increase with a decrease in the absorbed dose rate, an increase in the concentration of hydrazine, and the pH of the solution and attains hundreds of molecules per 100 eV of absorbed energy. It is hypothesized that the chain process includes a stage of formation of the N₂H₃ radical, its reaction with O₂, and the formation of O₂ ^– or N₂H₃O₂. The chain propagation reaction is due to the reaction of molecules of N₂H₄ with N₂H₃O₂ or O₂ ^–.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2450–2453, November, 1989.     

SO2 oxidation in aqueous solutions of Cu(II)

Kinetic studies of SO₂ oxidation by Cu(II) complexes in aqueous solutions containing halide ions X(X=Cl^–, Br^– and I^–) indicate that the highest activity is observed for mixed chloro-iodo complexes of Cu(II). A reaction mechanism is suggested where the principal role is assigned to CuX ₄ ^2– aq complexes and HSO₃ radicals.

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SO₂ Cu(II) , X(X=Cl^– Br^–, I^–). , - Cu(II). CuX^2–aq HSO₃.

     

Sulphur dioxide oxidation in aqueous solutions containing metal cations

Effect of vanadium cations as model inhibitors on SO₂ oxidation with air in iron sulfate solutions at 298–308 K has been studied and a mechanism of inhibition proposed.

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V, , SO₂ 298–308 K. .

     

Kinetics of oxidation of dioxanes by ozone in aqueous solutions

The kinetics of oxidation of dioxanes by ozone was investigated by a spectrophotometric method in the temperature interval of 281-311 K. The activation parameters of the reaction were determined.     

Radiation chemical oxidation of hydrazine in aqueous solutions containing oxygen

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, p. 1192, May, 1988.     

Pulse radiolysis study of one-electron oxidation of thionine in aqueous solutions

One-electron oxidation of thionine has been studied using specific oxidizing radicals such as Cl⁻Tl(II) and N₃ generated by pulse radiolysis of aqueous solutions. The semioxidized thionine exhibited threepK’s indicating four conjugate acid-base forms. N₃ radicals were found to be less efficient in oxidizing thionine as compared to Cl ₂ ⁻ , Tl²⁺ and Tl(OH)⁺. The rate constants for electron abstraction from thionine by Cl ₂ ⁻ , Tl²⁺, Tl(OH)⁺, Tl(OH)₂ and N₃ were evaluated. The spectra of different protonated forms of semioxidized thionine and the extinction coefficients at λ_max are presented. Reaction of OH radicals with thionine gave transient products whose spectra and acid-base properties were different from those of semioxidized thionine. The rate constant for formation of the product transient agrees well with competition kinetic value for reaction of OH with thionine reported earlier.     

Conductivity of aqueous solutions of fullerol synthesized by direct oxidation

The dependence of the specific conductance on the solute concentration for a solution of fullerol-d obtained by direct heterogeneous catalytic oxidation of C₆₀ at 25°C is investigated. Values of the molar conductivity and the apparent degree of dissociation and dissociation constant of fullerol-d are calculated. A qualitative charge-transport mechanism for the investigated solutions is proposed.     

Mechanism of electric spark dispersion of aluminum in aqueous solutions

Aluminum electroerosion was continued to be studied. The obtained experimental data confirmed the validity of the previously proposed mechanism of electric spark dispersion of aluminum. The composition of the oxide film forming on the surface of dispersed metal particles depends on the amount of atomic oxygen produced during electroerosion.     

Rate constants for one-electron oxidation by methylperoxyl radicals in aqueous solutions

Rate constants for one-electron oxidation by the methylperoxyl radicals (CH₃O₂, HOCH₂O₂, ^?O₂CCH₂O₂, and CCI₃O₂) in aqueous solutions have been measured by pulse radiolysis and found to be in the range of 3 × 10⁵ to 6 × 10⁸ M^?1 s^?1 for compounds with redox potentials between 0.6 and 0.1 V. Substitution on the methylperoxyl radical with OH or CO₂^? has only a minor effect on the rate of oxidation but substitution with three chlorines increases the rate constants by two orders of magnitude. The redox potential of the CH₃O₂ radical is estimated to be 0.6–0.7 V.     

Mechanism of anodic oxidation of tungsten in neutral sulphate-fluoride solutions

The anodic oxidation of tungsten has been studied in 1 M Na₂SO₄ solutions containing 0–0.25 M NaF. Steady-state currents measured in the passivation and passivity ranges increase significantly with increasing fluoride concentration, indicating enhanced dissolution of the oxide film. The electrochemical impedance response is dominated by the processes in the barrier layer and at its interface with the electrolyte. The presence of a pseudo-inductive loop in the impedance spectra at intermediate frequencies indicates point defect interaction during film growth and dissolution processes. A kinetic model including the recombination reaction between oppositely charged point defects at the film/solution interface as well as a kinetic scheme for tungsten dissolution through the film mediated by cation vacancies is proposed. It is found to reproduce satisfactorily the steady-state currents and the impedance spectra in the potential range 0.2–2 V. Such a model for the conduction mechanism in the barrier layer is believed to be an essential part of a modelling approach to the formation of a nanoporous overlayer on tungsten in fluoride-containing solutions.