The elementary stages of electroreduction of alkyl(hetero)arylsulfones in water-organic media

Intermediates (IM) of methyl(2-pyridyl)sulfone (MPS) and tert-butyl(2-pyridyl)sulfone (TBPS) formed upon the transfer of the first electron are studied by methods of laser photoelectron emission (LPE). The capture constants of solvated electrons by the MPS and TBPS molecules were determined. The time-resolved voltammograms of each sulfone measured in water-organic mixtures (20–80% ethanol or 60% DMSO) are found to demonstrate a redox wave with half-wave potentials E _1/2 = −1.34 and −1.37 V for MPS and TBPS, respectively. The dependence of rate constants for the one-electron IM reduction and oxidation on the potential is shown to obey the slow-discharge equation and the absolute magnitudes of rate constants are determined. The characteristic times of homogeneous transformations (decomposition, protonation) of MPS and TBPS radical anions do not exceed 3 × 10⁻⁷ s. The LPE data are compared with the results of preparative electrolysis and the mechanisms of both electrochemical and homogeneous reactions of IM are discussed.     

Temperature-dielectric spectroscopy of aqueous solutions using the method of capillary-waveguide resonance

We study the temperature dependences of the frequency characteristics of a capillary-waveguide resonator for strongly absorbing media. The temperature influence on the frequency, Q-factor, and absorption depth in the studied resonance is theoretically revealed and experimentally confirmed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 8, pp. 711–716, August 2008.     

Photoelectric Properties of Polyimide Containing J-Aggregates of Cyanine Dyes

Photoelectric characteristics were measured for photorefractive aromatic polyimides containing nanocrystalline J-aggregates of thiacarbocyanine dyes, which are responsible for the photoelectric sensitivity at the Ar–Kr laser emission wavelength of 647 nm. The amplitude and the speed of writing of the photorefractive diffraction grating were determined by the stationary value of the ratio (j _ph + j _d)/j _d and by the rate of the growth of photocurrent j _ph to the stationary value, respectively. The dependence of the quantum yield of free charge carriers on the applied electric field was linear in the vs. (E ₀)^3.5 coordinates. Experimental results fitted well to the curve calculated up to (E ₀)⁴ according to the Onsager equation with the initial quantum yield of the bound electron–hole pairs assumed to be ₀ = 0.2 and the charge separation distance in the pair of r ₀ = 12 Å.     

Thermodynamic and kinetic characteristics of intermediates of electrode reactions: A comparative investigation of a number of alkylaryl and alkyl halide radicals by the laser photoemission methods

A comparative investigation of thermodynamic and kinetic properties of a number of alkylaryl intermediates (benzyl and benzhydryl radicals) and alkyl halide intermediates (chloromethyl, dichloromethyl, and trifluoromethyl radicals) is performed by methods of laser photoemission. Techniques, aimed at the determination of thermodynamic and kinetic properties of intermediates (standard potentials E ⁰ of redox pairs R/R^-, standard adsorption free energies -G _a(R) ⁰ , values of rate constants W ⁰ at an equilibrium potential, as well as lifetimes (times of death in the bulk) _R of radicals R and _X of products of their reduction R^-) from a comparison of Tafel plots for quasi-reversible reduction of intermediates with calculated ones and standard potentials E ⁰—from Tafel plots for irreversible electroreduction of intermediates, are presented. The transition from irreversible to quasi-reversible reduction in aprotic solvents at EE ⁰ is observed only in the case of benzyl, benzhydryl, and trifluoromethyl radicals, for which this particular collection of thermodynamic and kinetic properties is obtained, and is not observed for the chloromethyl and dichloromethyl radicals. In this case redox characteristics of intermediates (E ⁰, W ⁰) are estimated from absolute values of rates of their electroreduction. Possible reasons for the differences in the probability of a reversible electron transfer are discussed for the systems studied.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 157–174.Original Russian Text Copyright © 2005 by Krivenko, Kotkin, Kurmaz.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Kinetics of wetting of a compacted powder by aqueous solutions of surface active agents

Summary The capillary rise of aqueous solutions of anionic wetting agents into a compacted powder of an organic chromium complex is discussed on the basis of the Washburn-Rideal equation expanded to account for the porous structure parameters.At the porosity 1 —/6, corresponding to the loosest packing of monodisperse spheres the penetration rate is found to be mostly governed by the effective tensions operative at the moving three phase line of contact in case no deflocculation intervenes.

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Zusammenfassung Der Kapillaraufstieg wässeriger Lösungen anionischer Netzmittel in gepreßtem Pulver eines organischen Chrom-Komplexes wird durch die erweiterte Gleichung vonWashburn-Rideal wiedergegeben, in der die Parameter der porösen Struktur mit einbezogen werden.Bei der Porosität 1 —/6, die der lockersten Anordnung gleichförmiger Kugeln entspricht, wird die Eindringgeschwindigkeit meistens durch die an der sich bewegenden Dreiphasengrenze wirkenden Grenzflächenspannungen bestimmt, wenn keine Peptisation eintritt.

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Paper presented at the XII Intern. Congr. Fat Research, Milan, September 1974.     

Photocurrent kinetics during electron emission from metal into electrolyte solution: Part III. H3O+ solutions

The photocurrent kinetics in acid solutions have been investigated. The diffusion coefficients of atoms H?((7±2)×10^?5cm²s^?1) and D?((4±1)×10^?5cm²s^?1) and OH^? and OD^? radicals ((1±0.3)×10^?5cm²s^?1) are found. The rate constants of capture of solvated electrons by H₃O⁺ and D₃O⁺ ions are identical and equal to (8±1)×10⁹M^?1s^?1. From the shape of the kinetic curves it follows that electrochemical desorption of atomic hydrogen occurs from the adsorbed state. The rate constant of this process has been measured. It is shown that the rate constant of electrochemical desorption depends only slightly on the potential.     

Effect of the EDL Structure on the Mechanism of Electroreduction of Adsorbed Intermediates

Effect of the ₁ potential on various kinetic modes of the -hydroxyethyl radical reduction is studied using laser photoemission (LPE). A charged proton donor is found to make no impact on the electron transfer rate during the reduction of adsorbed radicals. Experimental results fit the model proposed earlier for the electroreduction of intermediates, which includes two parallel pathways for electron transfer—onto an adsorbed radical and onto a metastable complex radical–proton donor. Demonstrated is a complete analogy between time-resolved voltammograms for LPE-generated intermediates and classic polarograms.