Kinetics and Mechanism of Palladium Electrodeposition from Alkaline Solutions of Palladium(II) Bisethylenediamine Complexes

The electroreduction kinetics of Pd(en)²⁺ ₂ complexes (0.01 M) is studied on a rotating disk electrode of Pd by recording CVA at 25, 50, and 70°C in solutions of pH 12–13 at ethylenediamine concentrations of 0.03–1.0 M. Established is a diffusion nature of limiting currents, from which diffusion coefficients for Pd(en)²⁺ ₂ complexes are calculated. The Pd electrode capacitance, determined by a pulsed galvanostatic method, is used for taking into account the true surface areas of electrolytic Pd deposits. Parameters of the slow electrochemical stage, which involves Pd(en)²⁺ ₂ complexes, are determined. The temperature dependence of the rate constant of cathodic reduction of Pd(en)²⁺ ₂ complexes is used for calculating an apparent activation energy. An electroreduction mechanism of Pd(en)²⁺ ₂ complexes on a Pd electrode is discussed.     

Effect of the nature of the metal oxide on selective transformation of methane under unsteady conditions in the absence of oxidant in the gaseous phase

The catalytic transformation of methane into higher hydrocarbons was studied under unsteady conditions on oxides of various metals (Pb, Fe, Nb, Ti, Cd, Mo, Mg, Zn, Zr, Bi, Mn), and also on Sr-, La-, Y-, and Mn-containing oxides of perovskite structure. It is shown that the effectiveness of the catalysts not only depends on their chemical composition, but also is determined to a considerable degree by the specific surface of the oxides. L. V. Pisarzhevskii Institute of Physical Chemistry, Academy of Sciences of Ukraine, 252039 Kiev, Prosp. Nauki, 31, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 2, pp. 91–95, March–April, 1997.     

Molar volumes and ion pairing of lithium halides in alcohols

The concentration dependence of the apparent molar volumes of lithium halides (and electrolytes in general) in alcohols (and solvents permitting association in general) is, in the first instance, due to changes in the degree of association and to the inherent difference between the apparent molar volumes of the ions and of the ion pairs. Previous publications on the molar volumes of electrolytes in organic solvents, disregarding altogether ion pairing, appear to be incorrect. Data from the literature for lithium chloride and lithium bromide in normal primary alcohols and several branched alcohols from C₁ to C₈ and data from our laboratory for lithium halides in 1-hexanol and 2-ethyl-1-hexanol served for the determination of φ _V and φ _E . Electrical and structural contributions to the values of these functions for the ions and for the ion pairs are discussed.     

Electroreduction of benzo-1,2,3-dithiazolium salts and their selenium analogs in nonaqueous solution

The electroreduction of benzo-1,2,3-dithiazolium cations and their selenium analogs in aprotic solvents takes place in two steps. The first step is a reversible, one-electron transfer leading to the formation of stable radicals detected by EPR. As a result of further electroreduction, the radicals obtained combine with six electrons to form the corresponding o-aminothio(seleno)phenols. Analysis of the reduction potentials of the compounds studied shows that the substitution of a selenium atom for a sulfur in these cations, especially in the 2 position of the heterocycle, facilitates their electrochemical reduction. The electrochemical activity and the kinetics of nulceophilic substitution in the cations studied are compared.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 219–222, February, 1985.     

Isolation of a urease from watermelon seeds and the study of its properties

The enzyme urease has been isolated from the seeds of the watermelon of the Ogonek variety and has been characterized. The molecular weight of a rechromatographed sample of the enzyme has been determined as 480,000. The pH dependence of the activity of the urease and the kinetic parameters of the enzyme have been studied.All-Union Scientific-Research Institute of the Chemistry and Technology of Drugs, Khar'kov. Vitaminy Scientific-Production Amalgamation, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 624–628, September–October, 1983.     

Oxidation with permanganate in presence of fluoride potentiometric determination of manganese(II)

The effects of acidity, fluoride concentration, temperature and concentration of manganese in the reaction between KMnO(4) and Mn(II) were studied potentiometrically. The rate of reaction is increased by increasing the fluoride concentration and/or decreasing the acidity of the solution. The formal redox potentials of the MnO(-)(4)/Mn(III) and the Mn(III)/Mn(II) systems were determined at different pH values. The E degrees values obtained by extrapolation to pH = 0 were 1.58 and 1.52 V respectively. The amount of Mn(II) determined was varied from 5 to 56 mg. The net reaction can be represented as MnO(-)(4) + 10HF(-)(2) + 4Mn(2+) right harpoon over left harpoon 5MnF(-)(4) + 2H(+) + 4H(2)O.     

Synthesis and spectral study of chelate alkenylarenedicarbonyl complexes of Cr,Mo and W

Irradiation of alkenylarene tricarbonyl-chromium, -molybdenum, and -tungsten compounds in which the double bond is separated from the arene moiety by a two- or three-atom bridge results in intramolecular cyclization to give stable chelate alkenylarenedicarbonylmetal complexes. Chelate complexes containing four-atom bridges have low stabilities, and those with monoatomic bridges were not formed at all. Irradiation of styrenetricarbonyl-chromium and -molybdenum leads to dinuclear tricarbonylmetal—dicarbonylmetal complexes. The chelate complexes obtained have been studied by IR, proton NMR, and ¹³C NMR spectroscopy. The electron density distributions and the stereochemistry of the complexes are discussed. With nonsymmetric arenes, diastereoisomers are formed; the predominant isomers have been isolated in the pure form. According to the proton NMR data the double bond in alkenylarenechromium chelates is parallel of nearly parallel to the arene ring plane.     

Polarographic reduction of adenine and its 9-(α,ω-dihydroxy-2-alkyl) derivatives

The polarographic reduction of adenine and its 9-(,)-dihydroxy-2-alkyl) derivatives on a short-period mercury electrode in strongly acidic media is determined by the rate of diffusion of the corresponding cations and, at pH values that exceed the pK_a values, by the kinetics of surface protonation of the uncharged molecules; this was proved by the dependence of the limiting current on the height of the mercury column, the temperature, and the depolarizer concentration. The polarographic reduction of adenine, adenosine, 9-(,-di-hydroxy-2-alkyl)adenines, and the corresponding phosphates in acidic media proceeds with the loss of sic electrons per molecule. The similar trends of the change in the half-wave potentials and the numerical pK_a values is associated with the fact that the site of protonation is simultaneously the site of nucleophilic attack by the electron during electrical reduction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1675–1678, December, 1977.     

Epoxy Composites Modified with Finely Dispersed Fillers

The thermal stability and mechanical strength of composites based on ED-20 epoxy oligomer cured with isomethyltetrahydrophthalic and methylendic anhydrides was studied as influenced by the nature and properties of finely dispersed inorganic fillers, such as carbon black, aluminum oxide, and silica nanoparticles.     

State of Chromium in Solid Solutions of Multicomponent Bismuth Niobates with Pyrochlore Structure

Magnetic susceptibility of solid solutions of multicomponent bismuth niobates with pyrochlore structure containing chromium atoms was studied. The parameters determining the state of chromium atoms and the exchange coupling between the paramagnetic atoms were calculated. The best agreement between the experimental and theoretically calculated magnetic moments of the chromium atoms is observed on the condition that all the chromium atoms in the Bi₂MgNb₂O₉ structure are in the form of ferromagnetic exchange-coupled dimers with an exchange parameter J 18 cm^{- 1}.