Micro-heterometric determination of cadmium with sodium diethyldithiocarbamate

0.5 mg of Cadmium in 20 ml aqueous solution can be determined heterometrically at 20°C with sodium diethyldithiocarbamate. The solution may contain 99–99.9% of Ca, Ba, Mg, Zn, Mn, Al, Cr(lll), Fe(III), Sb(III) or Pb. Titration time: 10–15 min. Error generally 0–1%.     

Catalytic-kinetic absorptiostat technique with the indigo carmine—hydrogen peroxide reaction as the indicator reaction

The absorptiostat method previously described is used for the catalytic-kinetic determination of sulphur compounds (sulphide, thioacetamide. thiourea and thiosulphate) in the micromolar range by means of their catalytic action for the indigo carmine—hydrogen peroxide indicator reaction. The thiosulphate catalyst is activated by iron(III) or aluminium(III); aluminium(III) is deactivated by fluoride. On this basis, iron(III) is determined in the ng range, and aluminium(III) and fluoride in the μg range.     

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.     

Spectrophotometric study of the reaction rate of 2,4-diaminophenol oxidation by hydrogen peroxide

The noncatalytic oxidation of 2,4-diaminophenol by H₂O₂ was studied. The corresponding rate constants were calculated and the activation energy was found.     

Catalytic-kinetic determination of substituted thioureas and thioacetamide by an absorptiostat method with bromopyrogallol red/hydrogen peroxide as the indicator reaction

In the absorptiostat method described, the concentration of the dyestuff in the bormopyrogallol red/hydrogen peroxide reaction is kept very low and constant by the automatic addition of increments of bromopyrogallol red solution. This is used in aqueous solutions at pH 4.0 to determine the catalysts thiourea, N-methylthiourea, N-allylthiourea and thioacetamide in the 0.1–1 mmol l^?1 range with only 0.5-ml samples. The catalytic activities of another nine substituted thioureas are described; they depend on the kind of N-substituents as has been shown before for the sodium azide/iodine reaction, but the sequence of activities for different compounds is quite different.     

Green oxidation with aqueous hydrogen peroxide

Aqueous H2O2 is an ideal oxidant, when coupled with a tungstate complex and a quaternary ammonium hydrogensulfate as an acidic phase-transfer catalyst. It oxidizes alcohols, olefins, and sulfides under organic solvent- and halide-free conditions in an economically, technically, and environmentally satisfying manner.     

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).     

Alcohols oxidation with hydrogen peroxide promoted by TPAP-doped ormosils

Organically modified silica gels doped with TPAP (tetra-n-propylammonium perruthenate) are effective catalysts for the oxidation of alcohols by hydrogen peroxide at room temperature, provided that the oxidant H₂O₂ solution is added slowly. The effect of the surface catalyst polarity is the opposite of that found in aerobic alcohols oxidation and is consistent with the polar nature of the primary oxidant.     

Catalytic oxidation of hydrocarbons with hydrogen peroxide by vanadium-based polyoxometalates

Vanadium compounds have attracted much attention because they have widely been used for homogeneous, heterogeneous, industrial, and biological oxidation processes with alkyl hydroperoxides, H₂O₂, and O₂. The present review summarizes recent developments for homogeneous and heterogeneous liquid-phase oxidation of hydrocarbons with H₂O₂ catalyzed by vanadium complexes and vanadium-based polyoxometalates including our recent studies on selective oxidation of hydrocarbons with H₂O₂ catalyzed by divanadium-substituted polyoxotungstates, [γ-SiW₁₀O₃₆V₂(μ-OH)₂]^4? (I) and [γ-PW₁₀O₃₆V₂(μ-OH)₂]^3? (II).     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-palygorskite

Palygorskite-supported Sn complexes were prepared by a simple procedure. Cyclic ketones and acyclic ketones were oxidized by hydrogen peroxide in a reaction catalyzed by palygorskite-supported Sn complexes, affording corresponding lactones or esters with selectivity for the product of 90-100%. The catalysts can be recycled for several times without significant decline in catalytic activity.     

Iodine oxidation by hydrogen peroxide and Bray-Liebhafsky oscillating reaction: effect of the temperature

This work presents a new experimental kinetic study at 39° and 50° of the iodine oxidation by hydrogen peroxide. The results allow us to obtain the temperature effect on the rate constants previously proposed at 25° for our model of the Bray-Liebhafsky oscillating reaction (G. Schmitz, Phys. Chem. Chem. Phys. 2010, 12, 6605.). The values calculated with the model are in good agreement with many experimental results obtained under very different experimental conditions. Numerical simulations of the oscillations observed formerly by different authors are presented, including the evolutions of the iodine, hydrogen peroxide, iodide ions and oxygen concentrations. Special attention is paid to the perturbing effects of oxygen and of the iodine loss to the gas phase.     

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⁺ .

     

Effect of di-2-ethylhexyl sodium sulfosuccinate reversed micelles on the iron-tetrasulfonatophthalocyanine-catalyzed fluorogenic oxidation reaction of L-tyrosine with hydrogen peroxide.

The catalytic behavior of iron tetrasulfonatophthalocyanine (FeTSPc) for the oxidation reaction of L-tyrosine with H2O2 in a di-2-ethylhexyl sodium sulfosuccinate (AOT) reversed-micellar system (AOT/cyclohexane) was studied. It was indicated that the reversed micelles could not only enhance the catalytic activity of FeTSPc, but could also increase the fluorescence intensity of the product. Factors that may influence the catalytic reaction, including the concentration of AOT, the cosolubilized water, temperature and pH, were further examined. The possibility of its analytical application was also tested. Experimental results show that the calibration graphs for the determinations of FeTSPc and H2O2 under optimum conditions are linear over the range of 1.0 x 10-8 - 1.0 x 10(-6) mol L(-1) and 0.0 - 3.0 x 10(-6) mol L(-1), respectively, with detection limits of 1.1 x 10(-9) mol L(-1) and 3.1 x 10(-9) mol L(-1) for FeTSPc and H2O2, respectively.     

Catalytic oxidation of aldehydes to carboxylic acids with hydrogen peroxide as oxidant

Alkyl and aryl aldehydes were catalytically oxidized to carboxylic acids in high yields with hydrogen peroxide as oxidant using benzeneseleninic acid as catalyst.     

Oscillatory reactions involving hydrogen peroxide and thiosulfate-kinetics of the oxidation of tetrathionate by hydrogen peroxide

The reaction between tetrathionate and hydrogen peroxide forms an important part of several pH oscillators based on the oxidation of thiosulfate. The kinetics of this reaction were examined in a batch reactor by measurement of the initial pH values in the range from 8 to 10.5. Experimental data were evaluated by the method of initial reaction rates combined with the assumption of instantaneously equilibrated acid-base reactions. The rate-determining step was found to be of the first order with respect to tetrathionate, hydrogen peroxide, and OH- ions with the value of rate constant k = (1.50 +/- 0.03) x 10(2) (M2 s)(-1) at 25 degrees C. In the alkaline solution, no distinct catalytic effect of Cu2+ was observed in contrast to earlier assumptions. The waveform of measured pH over the course of the reaction indicates that thiosulfate is probably an intermediate because characteristics of the curves are very similar to those for the oxidation of thiosulfate. We also measured the time evolution of concentrations of major components by the attenuated total internal reflectance infrared spectroscopy to further elucidate the underlying reaction mechanism. These measurements confirm the suspected role of thiosulfate as an intermediate in the studied reaction and provide valuable detailed information on the time evolution of thiosulfate, sulfite, sulfate, tetrathionate, and trithionate. These experimental observations are included in a simple mechanism that accurately simulates the reaction course in an alkaline solution. The results provide considerable new insights into the nature of autocatalysis in the hydrogen peroxide-thiosulfate-Cu2+ reaction and suggest that a new role for Cu2+ in the oscillatory dynamics observed in a flow-through reactor needs to be found.     

The oxidation of cinnamaldehyde with alkaline hydrogen peroxide

The oxidation of cinnamaldehyde (3-phenyl-2-propenal) by alkaline peroxide results in epoxidation of the double bond to form cinnamaldehyde epoxide (3-phenyl-2,3-epoxy-propanal) which undergoes further reaction by ring opening and side chain cleavage to yield benzaldehyde and acidic fragments. The reactions are first-order in the organic substrates and perhydroxyl anion and second-order overall. In the presence of alkali alone, two further reactions take place in which cinnamaldehyde and cinnamaldehyde epoxide side chains are cleaved by reaction with hydroxide ion to form benzaldehyde and side chain fragments. These reactions are first-order in the organic substrates and hydroxide ion and second-order overall. Increasing solvent polarity accelerates the rates of reaction and reaction mechanisms have been proposed to describe the observed kinetic behavior. The stereoselectivity of the epoxidation reaction has been examined in terms of an existing model for epoxidation of α, β-unsaturated ketones by alkaline peroxide. © 1993 John Wiley & Sons, Inc.     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-aniline complex

Sn-aniline complex was prepared by a simple procedure.Cyclic and acyclic ketones were oxidized into lactones or esters with very high selectivity and yield with 30% hydrogen peroxide in the presence of Sn-aniline complex.