Kinetics of the molybdate catalyzed oxidation of iodide by hydrogen peroxide

The kinetics of the oxidation of iodide by hydrogen peroxide catalyzed by acidic molybdate have been studied by a spectrophotometric stopped-flow method. The results are interpreted in terms of the mechanism and the implied rate law where [mol] is total analytical concentration of molybdate. The values obtained for the rate and equilibrium constants are k₄ = (3.3 ± 1) × 10² 1./mole · s, K₁ = (1.2 ± 0.6) × 10⁴ 1./mole, K₂ = (1.3 ± 0.7) × 10³ 1./mole, and K₃ = (4 ± 3) × 10² 1./mole at 298°K.     

Ru(III)-EDTA catalyzed oxidation of ascorbic acid by hydrogen peroxide in aqueous solution

The kinetics of oxidation of ascorbic acid to dehydroascorbic acid by hydrogen peroxide catalyzed by ethylenediaminetetraacetatoruthenate(III) has been studied over the pH range 1.50 – 2.50, at 30°C and μ = 0.1 M KNO₃. The reaction has a first-order dependence on ascorbic acid and Ru(III)-EDTA concentrations, an inverse first-order dependence on hydrogen ion concentration, and is independent of hydrogen peroxide concentration in the pH range studied. A mechanism has been proposed in which ascorbate anion forms a kinetic intermediate with the catalyst in a pre-equilibrium step. Ruthenium(III) is reduced to ruthenium(II) in a rate-determining step and is reoxidized with hydrogen peroxide back to the Ru(III) complex in a fast step.     

The oxidation of aminophenazone by hydrogen peroxide

Aqueous solutions of aminophenazone were oxidized by excess hydrogen peroxide in acidic, neutral and alkaline media and the reaction was followed using thin-layer chromatography and spectrophotometry in the visible and uv regions. The oxidation course is explained on the basis of detection of the products formed (4-methylaminoantipyrine, 4-aminoantipyrine, 1-phenyl-3-methyl-4-(phenylazo)-5-pyrazolone, 1-acetyl-1-methyl-2-di-methyl-oxanil-2-phenylhydrazine, oxalic acid, dimethylamine).     

Troilite oxidation by hydrogen peroxide

The kinetics and mechanism of troilite oxidation by H(2)O(2) was studied at temperatures of 25 and 45 degrees C. Solutions within the range 0.1-0.85 mol L(-1) H(2)O(2) in HClO(4) (0.01-0.1 mol L(-1)) were used as dissolution media. The experimental amount of dissolved iron was plotted versus t(n), with n ranging from 0.25 to 1.55. The theoretical interpretation of this dependence suggests that the troilite oxidation involves several processes: Both experimental results and theoretical considerations illustrate the importance of temperature, pH, and [H(2)O(2)] for the kinetics and mechanisms of troilite oxidation. The amounts of dissolved iron strongly increase with temperature and [H(+)], whereas an increase of H(2)O(2) concentration seems to reduce the troilite oxidation. The reaction orders with respect to [H(+)] are variable, pointing out notable modifications of reaction mechanism with experimental conditions. The estimated value E(a)=25.4+/-0.9 k J mol(-1) ([H(2)O(2)]=0.4 mol L(-1) and pH 1) points to dissolution kinetics controlled by a mix regime of surface reaction and diffusion.     

The kinetics of oxidation of bilirubin and ascorbic acid in solution

The results of a comparative study of the oxidation of bilirubin, ascorbic acid, and their mixture in aqueous solutions under the action of air oxygen and hydrogen peroxide are presented. The observed and true rate constants for the oxidation reactions were determined. It was shown that the oxidation of tetrapyrrole pigment occurred under these conditions bypassing the stage of biliverdin formation to monopyrrole products. Simultaneous oxidation of bilirubin and ascorbic acid was shown to be accompanied by the inhibition of ascorbic acid oxidation by bilirubin, whereas ascorbic acid itself activated the oxidation of bilirubin.     

The ferric ion catalyzed decomposition of hydrogen peroxide in perchloric acid solution

Predictions of the “redox” and “complex” schemes for the Fe³⁺ catalyzed decomposition of H₂O₂ have been compared with published and new experimental data by numerical integratior of the appropriate complete sets of differential equations. Apparent discrepancies for the redox scheme at high Fe³⁺/H₂O₂ ratios are shown to disappear in the complete treatment, and inconsistencies of the complex scheme with both kinetic data and spectroscopic measurements are pointed out.     

Molybdenum(VI) catalysis of perborate or hydrogen peroxide oxidation of iodide ion

Summary Perborate in aqueous solution generates H₂O₂; in its presence the molybdenum(VI) catalysed oxidation of iodide ion is first order with respect to the oxidant and catalyst, and is independent of [I^–] and [H⁺]. Kinetic studies point to peroxymolybdenum(VI) species as the oxidizing species.     

过氧化氢水溶液催化氧化环戊烯制备戊二醛

用过氧化氢水溶液氧化环戊烯制得戊二醛。对多种催化剂-溶剂体系进行了试验, 在钨酸-叔丁醇体系中得到了最高的戊二醛得率: 近60%(30%过氧化氢水溶液为氧化剂)或80%(50%过氧化氢水溶液为氧化剂)。同时, 对该反应的机理进行了初步研究, 提出环戊烯被过氧化氢氧化为戊二醛是经过环氧化物中间产物的观点。     

Kinetic, mechanistic, and thermodynamic investigations on ferrofluid-catalyzed oxidation of L-ascorbic acid by hydrogen peroxide in acidic aqueous solution

The reduction of ferrofluid (FF) by L-ascorbic acid (H(2)A) and the reoxidation of the reduced FF to its original form by hydrogen peroxide have been investigated in aqueous acidic medium. The rate of reduction of FF was found to be first order with respect to [H(2)A] and [FF] and independent with respect to [H(2)O(2)] and ionic strength. The rate of reduction of FF increased with increasing pH (2.5-4.0), having an inverse first order dependence in [H(+)]. With increasing temperature (15-45 degrees C), the rate of reduction was increased in line with the Arrhenius equation. Based on experimental evidence and results a mechanism, operative to reduce FF and reoxidize the reduced FF by H(2)O(2), which makes the system catalytic, is suggested. Thermodynamic quantities associated with FF-catalyzed oxidation of H(2)A by H(2)O(2) were determined and compared with other closely related systems.     

Determination of carbon-bonded sulfur in soils by hydriodic acid reduction and hydrogen peroxide oxidation

A sequential extraction method has been developed for the determination of carbon-bonded sulfur in soils. The soil sample has been sequentially reduced with HI and oxidized with hydrogen peroxide, and finally the residue has been digested with a mixture of nitric acid and perchloric acid. All inorganic sulfur components and ester sulfur has been reduced to H₂S by HI except the unreducible sulfur including pyritic sulfur, carbon-bonded sulfur and a previously unidentified sulfur fraction. Whereas a part of the carbon-bonded sulfur has been dissolved in the HI reducing solution another part of carbon-bonded sulfur was removed by hydrogen peroxide oxidation. The total carbon-bonded sulfur compose for oxic soils of the HI-dissolved sulfur and the H₂O₂-oxidized sulfur. However, because the pyritic sulfur can be completely decomposed by H₂O₂, this form of sulfur should be subtracted from the sum of the two sulfur fractions in case of anoxic soils. Unidentified sulfur components were also detected in the residue after the sequential extraction.     

Azo dye oxidation with hydrogen peroxide catalysed by manganese 1,4,7-triazacyclononane complexes in aqueous solution

A kinetic and mechanistic study is reported of the oxidation of a number of azonaphthol dyes with hydrogen peroxide in aqueous solution, catalysed by some mono and dinuclear manganese(IV) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN). The results of UV-Vis investigations, augmented by EPR and ESI-MS studies, are described for a series of experiments in which concentrations, pH and ionic strength have been varied. The reactions are characterised by an induction period followed by a relatively rapid oxidation. For the dinuclear manganese complex 2, these are consistent with an initial perhydrolysis of the manganese complex involving both the dye anion and HO2-, to give mononuclear manganese species and the operation of a catalytic cycle incorporating MnIIIL(OH)3, O = MnVL(OH)2 and MnIVL(OH)3 (L = Me3TACN) (cf. the reactions of peroxidase enzymes). ESI-MS results provide evidence for the formation and reaction (with the dye) of MnIVL(OH)3. With the mononuclear manganese complex MnIVL(OMe)3, there is a short lag-phase attributed to perhydrolysis by HO2- followed by the same catalytic cycle.     

Thiocyanogen as an intermediate in the oxidation of thiocyanate by hydrogen peroxide in acidic aqueous solution

The kinetics of the reaction of H2O2 with excess SCN- in acidic media was studied by use of Ti(IV) as an indicator for the concentration of H2O2. Pseudo-first-order behavior was realized by this method, and these data confirm the acid-catalyzed rate law and rate constant reported some 40 years ago for this reaction under conditions of excess H2O2. Under the same conditions except without Ti(IV), repetitive-scan spectra reveal the formation and decay of an intermediate that absorbs in the UV. In the proposed mechanism, HOSCN is produced in the first step and it is converted rapidly to (SCN)2 through its equilibrium reaction with SCN-. The observed intermediate is believed to be (SCN)2, which decays on a longer time scale. Excellent global fits of this mechanism to the repetitive-scan data are obtained with rate constants constrained by the Ti(IV) data and published previously in our study of the ClO2/SCN- reaction. These fits yield a spectrum for (SCN)2 that is characterized by lambda(max) = 297 nm and epsilon297 = 147 M(-1) cm(-1), in fine agreement with our prior report.     

Deprotection of dithioacetals using the tantalum(V) chloride catalyzed oxidation of iodide ion by hydrogen peroxide

Dithioacetals can be deprotected to afford carbonyl groups using the tantalum(V) chloride catalyzed oxidation of iodide ion by hydrogen peroxide under mild conditions.     

Determination of hydrogen peroxide by xenon trioxide oxidation

Aqueous xenon trioxide solution has been used as the oxidizing agent in three precise methods of analysis for hydrogen peroxide. A catalytic method, which utilizes hydrogen peroxide to initiate the reaction between t-butanol and xenon trioxide, is described for determining amounts of hydrogen peroxide as low as 0.9 microg or 36 parts per milliard (ppM). A direct spectrophotometric titration was found to have a lower limit of about 50 microg, or 20 ppM. An indirect titrimetric method was also used to determine hydrogen peroxide in amounts as low as 50 microg with a relative standard deviation of 4% which decreased to 1 % for amounts over 200 microg.     

Catalytic oxidation of monosubstituted phenols by hydrogen peroxide

Studies of kinetic peculiarities in hydroxylation of phenols by H₂O₂ in the presence of ferric sulfate have revealed general regularities of this process. A scheme of this process is suggested accounting for the stepwise conversion of Fe³⁺ into various complex forms. The reaction is suggested to take place in the coordination sphere of Fe³⁺.

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H₂O₂ . . , Fe³⁺ .