Kaoru Ogura

The electron transfer at a liquid/liquid interface studied by current-scan polarography at the electrolyte dropping electrode

Abstract Some novel systems are introduced as suitable for observing the electron transfer voltammograms and/or polarograms at the aqueous (W)/nitrobenzene (NB) interface. Among them, the polarographic processes with systems composed of hexacyanoferrate(II), hydroquinone or hydroxyl ion in W/7,7,8,8-tetracyanoquinodimethane (TCNQ) in NB, hexacyanoferrate(III) or Ce4+ in W/ferrocene (FC) or tetrathiafulvalene (TTF) in NB and permanganate in W/tetraphenylborate ion in NB were found to be reversible under appropriate conditions. The relation between the limiting currents in polarograms and the concentration of reactants either in W or NB is presented. On the basis of analysis of reversible polarograms at the W/NB interface and a comparison with voltammograms at a platinum electrode in W or in NB, the half-wave potentials are connected to the oxidation-reduction potentials of the reactants in each individual solution, W or NB.

The transfer of anions at the aqueus/organic solutions interface studied by current-scan polarography with the electrolyte dropping electrode

The transfer of such anions as halides, their oxo-acid anions and other polyatomic anions was investigated at the aqueous/1,2-dichloroethane, nitrobenzene, or chloroform interface. The polarograms were reversible for most of the anions and therefore it was concluded that the transfer processes of these anions are controlled by the diffusion of anions in the aqueous and/or organic solutions. The half-wave potentials, ΔV12, of the polarograms, which can be related directly to the transfer energies, are discussed on the basis of the ionic radii, crystallographic forms, and charges of the anions. As for monovalent anions, linear relationships were obtained between ΔV12 and the inverse of the thermochemical radii, irrespective of the kind of organic solvent. The analytical aspects of ion-transfer polarography in the determination of anions are also discussed.

Effect of temperature on ion transfer at the aqueous/organic solution interface studied by current-scan polarography with the electrolyte solution dropping electrode

Abstract The transfer of I−, BF4−4, ClO−4, sulphonate anions (RSO−3) and alkylammonium cations (R4N+ or RNH+3) was investigated at the aqueous/nitrobenzene or 1,2-dichloroethane interface in the temperature range from 4 to 80° C. The ion transfers were polarographically reversible for all ions at any temperature investigated. The standard Gibbs transfer energies from the aqueous to the organic solution, ΔGo,w ⇌ orgtr, were calculated from the half-wave potentials of ion transfer polarograms. The effect of temperature on ΔGotr for ions of small volume was explained by the electrostatic interaction between the ion and solvents taking into account the change in the dielectric constants of the solvents and the structure of water. The effect for such voluminous ions as RSO−3 and RNH+3 was elucidated by considering both the electrostatic and non-electrostatic solvation energies of ions. The non-electrostatic contribution to the change of ΔGotr with temperature is discussed from the viewpoint of the structural change of water.

Ion transfer at the interface between an aqueous solution in the presence of concentrated salts and an organic solution studied by polarography at the electrolyte solution dropping electrode

Abstract Voltammetry at the interface of two immiscible electrolyte solutions has been demonstrated as one of the best methods for the investigation of the dissolved states of rather hydrophobic ions (i z ) in an aqueous solution (W) or the transfer of i z from W to an organic solution, even in the presence of highly concentrated hydrophilic salts in W. Based on half-wave potentials and diffusion currents in the voltammograms (polarograms in the present case) observed with various kinds and/or concentrations of coexisting salts, the effects of the salts on the transfer energies of i z were obtained. Also, the dissolved states of i z in W in the presence of concentrated coexisting salts were evaluated, taking into account the dehydration of i z owing to the decrease in the water activity, the formation energy for a cavity to immerse i z into W, the dispersion force working on i z and the ion pair formation of i z with the coexisting counter ion.

A SIMPLE SYNTHESIS OF NOVEL EXTRACTION REAGENTS. 4-ACYL-5-PYRAZOLONE-SUBSTITUTED CROWN ETHERS

A synthesis of novel 4-acylpyrazol-5-one-substituted crown ethers metal-chelating reagents is described. 4-Acylpyrazol-5-one-substituted dibenzo-16-crown-5 1a, 4-acylpyrazol-5-one-substituted dibenzo-19-crown-6 1b, and bis(4-acylpyrazol-5-one)-substituted diaza-18-crown-6 1c were designed and synthesized by simple coupling reactions between α-chloro 4-acylpyrazol-5-one 3 and the corresponding crown ethers 2a–c. Compound 1a was found to be an effective and metal ion-selective extraction reagent.