On the mechanism of pyrocatechol oxidation in aqueous solutions containing Cu(II) and amino acids

Catalytic activity of Cu(II) amino acid complexes in pyrocatechol oxidation by oxygen has been studied. It has been found that the reaction is enhanced by Cu(II) histidine complexes whereas other amino acids are inactive.

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. , -, Cu(II)- .

     

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.

     

Cu(II)氧化抗坏血酸的动力学和机理

本文在总离子强度I=1.00mol.dm^-^3、[Cu^2^+]>>[H2A]、[H^+]>>[H2A]、无氧及无缓冲剂存在的条件下, 研究Cu(II)氧化抗坏血酸(H2A)的动力学和机理. 发现Cu(II)与H2A不发生配位反应, 但以Cl^-存在的情况下, 确有Cu(II)的H2A配合物生成, Cu(II)氧化H2A反应的速率方程为r={a+b[Cl^-]}[Cu^2^+]{[H+]+Ka}^-^2, 25℃时a和b值分别为4.08×10^-^4s^-^1和0.555dm^3.s^-^1.mol^-^1. Cu(II)氧化H2A反应的表观活化能为68.1KJ.mol^-^1. 根据动力学结果, 提出了反应机理, 并给出了配合物ClCuHA的结构形式.     

Kinetics and mechanism of diethanolamine degradation in aqueous solutions containing carbon dioxide

The problem of diethanolamine (DEA) degradation in gas-treating processes was quantified through a detailed kinetic study. This reaction was found to be catalyzed by CO₂, and degradation occurs in a successive manner to 3-(2-hydroxyethyl)oxazolidone-2, to N,N,N′-tris(2-hydroxyethyl)ethylenediamine and then to N,N′-bis(2-hydroxyethyl)piperazine. A reaction mechanism consistent with these observations was proposed and tested through kinetic analyses. A satisfactory kinetic model which can be of practical use was derived.     

Kinetics and mechanism of oxidation of cis-diaquabis(glycinato)chromium(III) by periodate ion in aqueous solutions

The kinetics of oxidation of cis-[Cr^III(gly)₂(H₂O)₂]⁺ (gly = glycinate) by $ {\text{IO}}_{ 4}^{ - } $ has been studied in aqueous solutions. The reaction is first order in the chromium(III) complex concentration. The pseudo-first-order rate constant, k _obs, showed a small change with increasing $ \left[ {{\text{IO}}_{ 4}^{ - } } \right] $ . The pseudo-first-order rate constant, k _obs, increased with increasing pH, indicating that the hydroxo form of the chromium(III) complex is the reactive species. The reaction has been found to obey the following rate law: $ {\text{Rate}} = 2k^{\text{et}} K_{ 3} K_{ 4} \left[ {{\text{Cr}}\left( {\text{III}} \right)} \right]_{t} \left[ {{\text{IO}}_{ 4}^{ - } } \right]/\left\{ {\left[ {{\text{H}}^{ + } } \right] + K_{ 3} + K_{ 3} K_{ 4} \left[ {{\text{IO}}_{ 4}^{ - } } \right]} \right\} $ . Values of the intramolecular electron transfer constant, k ^et, the first deprotonation constant of cis-[Cr^III(gly)₂(H₂O)₂]⁺, K ₃ and the equilibrium formation constant between cis-[Cr^III(gly)₂(H₂O)(OH)] and $ {\text{IO}}_{ 4}^{ - } $ , K ₄, have been determined. An inner-sphere mechanism has been proposed for the oxidation process. The thermodynamic activation parameters of the processes involved are reported.     

Kinetics of the homogeneous oxidation of hydrogen by platinum(II) and platinum(IV) chloro complexes in aqueous solution

The kinetics of the homogeneous oxidation of hydrogen in the Pt(II)–Pt(IV)–Cl^––H₂O system has been studied for the first time in conditions permitting to avoid the formation of Pt-black. It is shown that platinum (II) [Pt(II)Cl_i(H₂O)_4-i, where i=1, 2, 2], is active in the reaction, whereas the PtCl ₄ ^2– complex and platinum(IV) do not react with hydrogen.

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, Pt-, H₂ Pt^II–Pt^IV–Cl^––H₂O. (II) (Pt^IICl_i(H₂O)_4-i, i=1, 2, 3); PtCl ₄ ^2– (IV) .

     

Kinetics and mechanism of diethyl sulfide oxidation by sodium peroxoborate in aqueous solutions

The kinetics of diethyl sulfide (Et₂S) oxidation by aqueous sodium peroxoborate (Na₂[В₂(О₂)₂(ОН)₄]) solutions in a wide acidity range (from [HClO₄] = 1 mol/L to рН 12) has been studied using a kinetic distribution method. The kinetic data together with the results of ¹¹B NMR spectroscopy demonstrate that the monoperoxoborate B(O₂H) ₃ ^- (OH) and diperoxoborate B(O₂H)₂(OH) ₂ ^- anions are the active species in Et₂S oxidation by sodium peroxoborate at рН 8–12. It is assumed that, at a high acidity of the medium ([HClO₄] = 0.05–1.0 mol/L), peroxoboric acid (ОН)₂ВООН or its protonated form (OH)₂BOOH ₂ ⁺ are direct reactants along with Н₂О₂ and HOOH ₂ ⁺ .     

Hydrogen-free homogeneous catalytic reduction of olefins in aqueous solutions

Herein we report a study involving the homogeneous catalytic reduction of unsaturated substrates in aqueous solutions or water-organic solvent mixtures. The reduction of olefins has been carried out in the presence of catalytic amounts of [Fe(CN)5NH3](3-) and excess of NH2OH, which under mild reaction conditions can be used to reduce carbon-carbon unsaturations without affecting carbonyl functionalities and aromatic rings. To explore the scope of the catalytic reduction, a wide variety of representative unsaturated substrates have been examined. The steric effects of the substituents on the carbon-carbon multiple bond as well as the regioselectivity and stereoselectivity of the catalyst have been studied. The deuterium kinetic isotope effect on the catalytic reduction of double bonds in olefins has been analyzed, and no significant kinetic isotope effect was found. Among the great advantages of this novel procedure for catalytic reduction are that hydrogen and high pressures are not needed, the catalyst is inexpensive and easily prepared, and water as well as water-organic solvent mixtures can be used as reaction media.     

Kinetics and mechanism of the oxidation of iron(II) ion by chlorine dioxide in aqueous solution

The mechanism by which an excess of iron(II) ion reacts with aqueous chlorine dioxide to produce iron(III) ion and chloride ion has been determined. The reaction proceeds via the formation of chlorite ion, which in turn reacts with additional iron(II) to produce the observed products. The first step of the process, the reduction of chlorine dioxide to chlorite ion, is fast compared to the subsequent reduction of chlorite by iron(II). The overall stoichiometry is The rate is independent of pH over the range from 3.5 to 7.5, but the reaction is assisted by the presence of acetate ion. Thus the rate law is given by At an ionic strength of 2.0 M and at 25°C, k_u = (3.9 ± 0.1) × 10³ L mol^?1 s^?1 and k_c = (6 ± 1) × 10⁴ L mol^?1 s^?1. The formation constant for the acetatoiron(II) complex, K_f, at an ionic strength of 2.0 M and 25°C was found to be (4.8 ± 0.8) × 10^?2 L mol^?1. The activation parameters for the reaction were determined and compared to those for iron(II) ion reacting directly with chlorite ion. At 0.1 M ionic strength, the activation parameters for the two reactions were found to be identical within experimental error. The values of ΔH? and ΔS? are 64 ± 3 kJ mol^?1 and + 40 ± 10 J K^?1 mol^?1 respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 554–565, 2004     

Study of copper complexes in saturated and unsaturated aqueous ammonium oxalate solutions containing Cu(II) impurity

The influence of Cu(II) impurity on chemical equilibria in unsaturated and saturated ammonium oxalate (AO) aqueous solutions was investigated as a function of concentration _ci$c_{\text{i}}$ of impurity. Using the computer programme “Hyss” the species present in the solutions were analysed. It was found that in the aqueous solutions of ammonium oxalate containing Cu(II) ions the following species are formed: Cu²⁺, Cu(OH)⁺, Cu(OH)₂, CuC₂O₄⁰ and Cu(C₂O₄)₂²⁻ in addition to C₂O₄²⁻, HC₂O₄⁻, H₂C₂O₄ and (NH₄)₂C₂O₄⁰ species, and their concentration depends on concentrations _ci$c_{\text{i}}$ of Cu(II) impurity and c of ammonium oxalate. The dependences of solution pH and of absorbance A   and the corresponding wavelength λ$\lambda$ for unsaturated aqueous solutions on ammonium oxalate concentration c   containing different concentrations _ci$c_{\text{i}}$ of Cu(II) ions showed three well-defined regions characterised by transition values of solution pH or solute concentration c. Speciation analysis revealed that Cu²⁺ and CuC₂O₄⁰, CuC₂O₄⁰ and Cu(C₂O₄₎₂²⁻, and Cu(C₂O₄)₂²⁻ complexes are predominantly present in the solute concentration intervals c≤0.01$c\le 0.01$ mol/dm³, 0.01 mol/dm³ <c<0.03$<c<0.03$ mol/dm³ and c≥0.03$c\ge 0.03$ mol/dm³, respectively. The concentration interval range 0.01 mol/dm³ <c<0.03$<c<0.03$ mol/dm³ corresponds to the pH interval where Cu(OH)₂ is precipitated. It was found that the solubility of ammonium oxalate at 30 °$°$C increases practically linearly with an increase in the concentration of Cu(II) impurity. Speciation analysis of saturated aqueous solutions of ammonium oxalate revealed that Cu(II) ions contained in AO saturated solutions exist mainly as Cu(C₂O₄)₂²⁻-type complexes, and the increase in the solubility of AO in the presence of Cu(II) impurity is essentially due to an increase in the ratio of the concentrations of CuC₂O₄⁰ and Cu(C₂O₄)₂²⁻ species.     

Kinetics of alkaline chloramine-T oxidation of arginine monohydrochloride with and without catalytic action of Cu(II) ion

The kinetics of uncatalysed and Cu(II) catalysed oxidation of arginine monohydrochloride was investigated. Both reactions follow a singular order dependence each in oxidant and substrate. An inverse order dependence is reported with the alkali concentration. A plot of observed rate constant versus Cu(II) concentrations Cu(II)2.0×10^–5 M is linear; from the intercept the rate constant for the uncatalysed pathway was calculated. However, at high copper ion concentrations i.e. Cu(II)>2.0×10^–5 M a fixed value of rate constant was found for all catalyst concentrations. Added neutral salts show an insignificant effect on the reaction rate. Mechanisms were proposed for both cases and rate expressions were derived by applying steady state assumptions.

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Die Kinetik der alkalischen Chloramin-T-Oxidation von Arginin-monohydrochlorid mit und ohneCu(II) als Katalysator

Zusammenfassung Die Oxidation erfolgt sowohl mit als auch ohne Cu(II)-Katalysator in erster Ordnung bezüglich des Oxidationsmittels und des Substrats; inverse Ordnung wird bezüglich der Alkalikonzentration beobachtet. Bis zu einer Cu(II)-Konzentration von2×10^–5 M ist die Geschwindigkeitskonstante der Katalysatorkonzentration proportional; darüber wird eine konstantbleibende Geschwindigkeit beobachtet, die nun von der Cu(II)-Konzentration unabhängig ist. Neutralsalze haben keinen Effekt auf die Geschwindigkeitskonstante. Es wird für den katalysierten und unkatalysierten Reaktionsablauf ein Mechanismus vorgeschlagen und ein mathematischer Ansatz präsentiert.

     

Kinetics of the dissolution of copper metal in aqueous solutions containing unsaturated organic ligands and copper(II)

The kinetics of the dissolution of copper metal in an aqueous solution containing copper(II) and an unsaturated organic ligand was followed by using an automated flow-injection analysis technique to determine the concentration of copper(I) in solution as a function of time. The results suggest that the rate of dissolution of the copper metal is dependent on electron transfer between the copper(II) and copper atoms on the surface of the copper metal, and on the stabilization of copper(I) by the unsaturated organic ligand in solution.     

Kinetics and mechanism of palladium(II) catalyzed chromium(VI) oxidation of mercury(I) in aqueous sulphuric acid

The Cr^VI oxidation of Hg^I in an aqueous acid medium occurs to a modest extent only in presence of Pd^II and in H₂SO₄ above ca. 0.20 mol dm^–3. The reaction is first order in [Cr^VI] in the presence of Pd^II catalyst. The order in [Hg^I] is less than unity, whereas that in [Pd^II] is unity. Increase in [H₂SO₄] accelerates the reaction rate. The added products, Cr^III and Hg^II, do not significantly effect the reaction rate. A mechanism involving HCrO₄ ^– and PdCl⁺ as the reactive species of oxidant and catalyst respectively, is proposed. The reaction constants involved in the mechanism have been evaluated.     

Kinetics and mechanism of Oxidation of Diaqua(nitrilotriacetato)cobaltate(II) by Peroxodisulfate ion in aqueous acidic solutions

Kinetik und mechanismus der oxydation von diaqua(nitrilotriacetato)-cobaltat(II) durch peroxodisulfat in wäßrigsauren lösungen Die Kinetik der Oxydation von Co^II-NTA durch Peroxodisulfat (S₂O) in saurem Medium photometrisch untersucht. Die Stöchiometrie der Reaktion ist: 2Co^II-NTA^? + S₂O → 2Co^III?NTA + 2SO. Im pH-Bereich 4,2—5,4 folgt die Reaktion dem Geschwindigkeitsgesetz [H⁺] und [S₂O] sind die Wasserstoff- bzw. Peroxodisulfationen-Konzentration, K_H ist die Dissoziationskonstante des Co^II(NTA)H und k_H ist die Geschwindigkeitskonstante für den Elektronenübergang. Die Aktivierungsparameter werden mitgeteilt und der mögliche Mechanismus für den Elektronenübergang wird diskutiert.     

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.     

Kinetics of catalytic oxidation of aqueous sodium sulfite

A gas-lift bubble column was used to investigate the kinetics of the reaction between oxygen and aqueous solutions of sodium sulfite in the presence of cobalt sulfate catalyst. Reaction orders have been determined for the sulfite, catalyst, and oxygen under high and low oxygen partial-pressure conditions. Parts of this paper were presented at the Second International Conference on Chemistry in Industry, Saudi     

Kinetics of catalytic oxidation of aliphatic alcohols in aqueous alkaline solutions of copper phenanthroline complexes

The effect of Cu(II), phenanthroline, alcohol, NaOH and O₂ concentrations on the oxidation rates of alcohols in aqueous alkaline solutions has been studied and a reaction mechanism is proposed.

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Cu(II), , , NaOH, O₂ - . .

     

Kinetics of peroxodisulphate oxidation of octacyanomolybdate(IV) in concentrated aqueous salt solutions

Summary Rate constants are reported for the oxidation by peroxodisulphate ions of octacyanomolybdate(IV) in concentrated aqueous salt solutions containing up to 6 mol dm^–3 salt including mixed salt solutions. The dependence of the logarthm of rate constant on salt concentration is discussed in terms of ionic hydration enthalpies and B-viscosity coefficients. The analysis confirms that ion-pairs play a key role in determining reactivities in these systems.     

Studies on the behaviour of beta-ethylthioethylenethioglycollate in aqueous Ni(II) and Cu(II) solutions

The stability constants of the 1:1 and 1:2 complexes of nickel and copper(II) with beta-ethylthioethylenethioglycollic acid have been determined at 25 degrees at ionic strength 1.0 (NaClO(4)). The values for the nickel complexes are K(1) = 1.11 +/- 0.06 x 10(2) (spectrophotometrically) or 1.25 +/- 0.11 x 10(2) (potentiometrically) and K(2) = 3.04 +/- 0.24 x 10(2) (potentiometrically). The corresponding values for the copper complexes are K(1) = 1.27 +/- 0.02 x 10(3) or 1.28 +/- 0.03 x 10(3) and K(2) = 7.29 +/- 0.30 x 10(2).