Cation-independent electron transfer between ferricyanide and ferrocyanide ions in aqueous solution

Electron transfer between Fe(CN)(6)(3-) and Fe(CN)(6)(4-) in homogeneous aqueous solution with K(+) as the counterion normally proceeds almost exclusively by a K(+)-catalyzed pathway, but this can be suppressed, and the direct Fe(CN)(6)(3)(-)-Fe(CN)(6)(4-) electron transfer path exposed, by complexing the K(+) with crypt-2.2.2 or 18-crown-6. Fe((13)CN)(6)(4-)-NMR line broadening measurements using either crypt-2.2.2 or (with extrapolation to zero uncomplexed [K(+)]) 18-crown-6 gave consistent values for the rate constant and activation volume (k(0) = (2.4 +/- 0.1) x 10(2) L mol(-1) s(-1) and Delta V(0) = -11.3 +/- 0.3 cm(3) mol(-1), respectively, at 25 degrees C and ionic strength I = 0.2 mol L(-1)) for the uncatalyzed electron transfer path. These values conform well to predictions based on Marcus theory. When [K(+)] was controlled with 18-crown-6, the observed rate constant k(ex) was a linear function of uncomplexed [K(+)], giving k(K) = (4.3 +/- 0.1) x 10(4) L(2) mol(-2) s(-1) at 25 degrees C and I = 0.26 mol L(-1) for the K(+)-catalyzed pathway. When no complexing agent was present, k(ex) was roughly proportional to [K(+)](total), but the corresponding rate constant k(K)' (=k(ex)/[K(+)](total)) was about 60% larger than k(K), evidently because ion pairing by hydrated K(+) lowered the anion-anion repulsions. Ionic strength as such had only a small effect on k(0), k(K), and k(K)'. The rate constants commonly cited in the literature for the Fe(CN)(6)(3-/4-) self-exchange reaction are in fact k(K)'[K(+)](total) values for typical experimental [K(+)](total) levels.     

Oxidation of hydrogen chloride with hydrogen peroxide in aqueous solution

Evolution of chlorine into the gas phase upon mixing of aqueous solutions of hydrogen chloride and hydrogen peroxide was studied. The threshold hydrogen chloride concentration corresponding to the onset of the chlorine evolution was determined.     

Mechanism and kinetics of the reaction of ozone with sodium chloride in aqueous solutions

It is shown experimentally that Cl⁻ appreciably accelerates ozone decomposition in water (τ_1/2 = 1.5 h versus 6 h in pure water). The decomposition of ozone in NaCl solutions includes the reversible reaction of ozone with the chloride ion (O₃ + Cl⁻ → O₃⁻ + Cl) as the key step, which is followed by the development of a chain reaction in which chain propagation is performed alternately by the chlorine atom Cl and its monoxide ClO. The current concentrations of the chlorine atom are rather low ([Cl] ∼ 10⁻¹⁴ mol/l). The overall process is satisfactorily described by a first-order rate law with respect to ozone. The decomposition of ozone in aqueous solutions of NaCl is not accompanied by the formation of products other than oxygen. In particular, no noticeable amounts of hypochlorites and chlorates are observed. This is particularly significant for medicinal applications of ozonized isotonic solutions.     

Catalysis of the reaction of ozone with chloride ions by metal ions in an acidic medium

It was found that VO²⁺, Fe³⁺, Co²⁺, and Cu²⁺ ions catalyze the reaction of O₃ with Cl^- in an acidic medium. The dependence of the rate of Cl₂ liberation in the reaction of O₃ with Cl^- on the concentrations of H⁺, VO²⁺, Fe³⁺, Co²⁺, and Cu²⁺ ions in the reaction solution was studied. A reaction scheme was proposed to explain the experimentally found catalytic effects of these ions. The constants that characterize the steps of the proposed scheme were determined.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 147–152. Original Russian Text Copyright © 2005 by Levanov, Kuskov, Koiaidarova, Zosimov, Antipenko, Lunin.     

Ab initio study on the reaction mechanism of ozone with bromine atom

Ab initio calculations of the potential energy surface (PES) for the Br+O₃ reaction have been performed using the MP2, CCSD(T), and QCISD(T) methods with 6‐31G(d), 6‐311G(d), and 6‐311+G(3df). The reaction begins with a transition state (TS) when the Br atom attacks a terminal oxygen of ozone, producing an intermediate, the bromine trioxide (M), which immediately dissociates to BrO+O₂. The geometry optimizations of the reactants, products, and intermediate and transition states are carried out at the MP2/6‐31G(d) level. The reaction potential barrier is 3.09 kcal/mol at the CCSD(T)/6‐311+G(3df)//MP2 level, which shows that the bromine atom trends intensively to react with the ozone. The comparison of the Br+O₃ reaction with the F+O₃ and Cl+O₃ reactions indicates that the reactions of ozone with the halogen atoms have the similar reaction mechanism. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Importance of single electron-transfer in singlet oxygen reaction in aqueous solution : Oxidation of electron-rich thioanisoles

Oxidation of substituted thioanisoles by chemically generated singlet oxygen was investigated in polar aqueous media. The formation of the superoxide ion was observed during sulphoxidation of 4-hydroxythioanisole (4) in phosphate buffer at pH 7.5. Control experiments indicated that the superoxide ion was formed by a direct reaction between singlet oxygen and 4. The kinetics of the trapping reaction by diphenylsulphoxide indicated the involvement of a single intermediate. The overall rate constants of the reaction of thioanisoles with singlet oxygen in methanol-water (1:1) are one order of magnitude larger than those in benzene. On the basis of these results, a mechanism involving a charge-transfer complex has been proposed for the reaction of electron-rich thioanisoles with singlet oxygen, whereby the charge-transfer complex would produce persulphoxide directly or dissociate to the cation radical and superoxide ion in polar aqueous media.     

Oxidation of 5-aminouracil with molecular oxygen in aqueous solution in the presence of copper(II) chloride

5-Aminouracil was found to form a six-coordinate copper(II) complex in aqueous solution and undergo oxidation to 5,5,6-trihydroxypyrimidine-2,4(1H,3H)-dione in the presence of molecular oxygen. A scheme was proposed for the fixation and activation of molecular oxygen on six-coordinate copper(II) complex with 5-aminouracil. The effect of the ligand structure on the rate of its oxidation with molecular oxygen in aqueous solution in the presence of copper(II) ions was shown.     

Rate coefficient for the H atom reaction with acrylate monomers in aqueous solution

The rate coefficients of H atom addition to 20 acrylate type monomers were measured in dilute aqueous solutions by pulse radiolysis technique. All the measured values were in a relatively narrow range (2×10⁹-1×10¹⁰ mol⁻¹ dm³ s⁻¹). The rate coefficients changed in the following order: crotonates≈maleates<fumarates<acrylic acid esters≈acrylamides<methacrylic acid esters. Some correlation between the H and OH addition rate coefficients was found.     

Oxidation of 5-hydroxy-6-methyluracil with molecular oxygen in the presence of copper(II) chloride in aqueous solution

Oxidation of 5-hydroxy-6-methyluracil with molecular oxygen in the presence of copper(II) chloride involves formation of a 2 : 1 complex with copper(II). The rates of consumption of initial 5-hydroxy-6-methyluracil and oxygen were determined in the temperature range from 40 to 80°C. A probable reaction mechanism implies fixation and activation of molecular oxygen on the copper(II) complex with 5-hydroxy-6-methyluracil with formation of active oxygen species that are responsible for hydroxylation of the double C⁵=C⁶ bond in the uracil molecule.     

Re-evaluation of the rate constant for the H atom reaction with tert-butanol in aqueous solution

The rate constant (k) of the H+tert-butanol reaction at pH∼1–2 was measured by the time profile of the absorbance build-up of the tert-butanol radical and by competitive reactions for H atoms between maleic acid and tert-butanol. The determined rate constant, k=(1.15±0.2)×10⁶ mol⁻¹ dm³ s⁻¹, is nearly an order of magnitude higher than the previously published rate constants.     

Studies on the oxygen atom transfer reactions of peroxomonosulfate: Oxidation of glycolic acid

The kinetics of oxidation of glycolic acid, an α‐hydroxy acid, by peroxomonosulfate (PMS) was studied in the presence of Ni(II) and Cu(II) ions and in acidic pH range 4.05–5.89. The metal glycolate, not the glycolic acid (GLYCA), is oxidized by PMS. The rate is first order in [PMS] and metal ion concentrations. The oxidation of nickel glycolate is zero‐order in [GLYCA] and inverse first order in [H⁺]. The increase of [GLYCA] decreases the rate in copper glycolate, and the rate constants initially increase and then remain constant with pH. The results suggest that the metal glycolate ML⁺ reacts with PMS through a metal‐peroxide intermediate, which transforms slowly into a hydroperoxide intermediate by the oxygen atom transfer to hydroxyl group of the chelated GLYCA. The effect of hydrogen ion concentrations on k_obs suggests that the structure of the metal‐peroxide intermediates may be different in Ni(II) and Cu(II) glycolates. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 160–167, 2009     

Studies on the oxygen atom transfer reactions of peroxomonosulfate: Oxidation of lactic acid

Kinetics of oxidation of lactic acid by peroxomonosulfate (PMS) catalyzed by Ni(II) ions has been studied in aqueous buffered (sodium acetate‐acetic acid) medium. The reaction follows first order in [PMS] and [Ni(II)] and inverse first order in [H⁺]. The effect of pH on the rate suggests that both HSO and SO are the active forms of the oxidant. The intermolecular reaction between HSO and nickel lactate results in hydroperoxide intermediate in the rate‐limiting step. The deprotonated form of PMS, SO, gives a lactate‐nickel‐peroxomonosulfate intermediate, which then undergoes intramolecular oxidation–reduction reaction. The thermodynamic parameters also support the kinetic scheme. Comparison with (nickel) glycolate shows that the electron‐donating methyl group in lactic acid enhances the nucleophilic interaction of the α‐hydroxyl group. A suitable mechanistic scheme is also proposed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 449–454, 2009     

Colloidal copper and peculiarities of its reaction with silver ions in aqueous solution

Interactions between colloidal copper and silver ions lead to the formation of silver nanoparticles. The reaction proceeds through the intermediate stage of the formation of a copper-silver contact pair. The formation of bimetallic Ag_coreCu_shell nanoparticles is observed in the presence of the “seeding” silver nanoparticles and upon the simultaneous radiochemical reduction of Ag⁺ and Cu²⁺ ions.     

Kinetic relationships and mechanism of ozone reaction with polystyrene in CCl4 solution

In this work a study is made of the degradation on ozonation of unfractionated polystyrene (PS) in CCl₄ solution. It was found that the ozone attack of PS molecules is accompanied by hydrogen abstraction from tertiary CH bonds and by the formation of ozonides due to the reaction of ozone with the aromatic rings. A scheme of PS degradation in solution is suggested; several kinetic parameters are evaluated.     

Oxidation of chloride to chlorine in aqueous solution via redox catalysis

This study reports evidence for the generation of chlorine from NaCl as starting material when aqueous-solution oxidizing materials such as Ce(SO₄)₂·4H₂O, Suprox (perisophthalic acid), MPPA (monoperoxyphthalic acid) and NaBO₃·4H₂O are brought in contact with catalytic amounts of powdered RuO₂. Cl₂ evolution takes place, showing that very low energy losses occur when a suitable redox catalyst mediates the oxidation step.     

Charge transfer reactions of organic ions containing oxygen: Correlation between reaction energetics and cross sections

Cross sections for charge transfer reactions of organic ions containing oxygen have been obtained using time-of-flight techniques. Charge transfer cross sections have been determined for reactions of 2.0 to 3.4 keV ions produced by electron impact ionization of oxygen containing molecules such as methanol, ethanal and ethanol. Experimental cross section magnitudes have been correlated with reaction energy defects computed from ion recombination energies and target ionization energies. Large cross sections are observed for reacting systems with small energy defects.     

Oxidation of Fe2+ ions by transfer of energy from γ-irradiated NaCl in aqueous Fricke solution

The oxidation of iron/II/ ions has been studied by dissolving -irradiated NaCl crystals in aqueous Fricke solution. The yield of iron/III/ ions was determined as a function of the amount of NaCl added, storage time, dose, concentration of iron/II/ ions and pH of the Fricke solution. The energy transfer parameter, , which is the ratio of G/Fe³⁺/ obtained by the addition of irradiated NaCl to that by direct radiolysis was evaluated.     

Kinetics and mechanism of ketone-bisulfite addition reaction in aqueous solution

The kinetics of the addition of bisulfite to acetone has been studied by the polarographic technique. The specific rate increases with pH and hence the reaction is probably base catalyzed. Mechanisms have been suggested for the reaction in the presence and absence of added base.

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