Galina V. Simbirtseva

Generation of phenylmethylketyl radicals in aqueous solutions and study of their transformation

Acetophenone and its intermediates formed upon the first electron transfer are studied by laser photoemission and traditional electrochemistry. It is shown that the intermediate reduction is affected by competition of the reactions of the formed radical-anions oxidation and their subsequent transformation to secondary products that are rapidly reduced at the electrode. From the comparison of the data obtained by the laser photoemission method and electrochemical measurements a conclusion was drawn that the product is a metastable complex (associate) of the radical-anion with water molecule; its formation rate constant is rather low (∼6 × 103 M−1 s−1). It was also concluded that bulk radical reactions dominate in aprotic media at moderate cathodic potentials; the acetophenone radical-anion is reduced at E ≤ −1.9 V (SCE). This conclusion agrees with the results of the acetophenone preparative electrolysis in DMFA, where marked yield of pinacon was observed at the potentials of limiting current of the 1st reduction wave, while the stage of 2nd electron transfer occurred at E ≤ −2.3 V (SCE).

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

Effect of the Ψ1 potential on various kinetic modes of the β-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.

Investigation of electrochemical behavior of secondary products of capture of OH radicals by dimethyl sulfoxide molecules using laser photoemission

Electrode reactions of intermediates formed during capture of OH radicals by dimethyl sulfoxide (DMSO) molecules were studied using laser photoemission in aqueous buffer solutions in the pH range from acidic to basic. The results were compared with characteristics of one-electron reduction of methyl radicals generated via photoemission from methyl halides CH3X (X = Cl, I). From these experiments, it was concluded that intermediates in these systems were identical since the primary product of capture of OH radicals by DMSO molecules, i.e., adduct (CH3)2SO. (OH), was spontaneously decomposed to form .CH3 with a time as low as <2 × 10−5 s. Some anomalies were found on time-resolved voltammograms of intermediates in the pH range from weakly basic to weakly acidic and at illumination times of an electrode with UV light Tm ≤ 90–300 ms. These features were presumably caused by rather slow formation of organomercury intermediates as interaction products of the components of the system DMSO—OH radical—mercury electrode.

Electrochemical Behavior of Electrodes Containing Single-Walled Nanotubes

The differential capacitance and voltammograms of electrodes that contain single-walled carbon nanotubes are measured in aqueous electrolytes. The discovered dependence of the capacitance on the measurement frequency is attributed to structural features of nanomaterials used. Electrochemical characteristics of nanotube electrodes are close to those of glassy carbon electrodes, with the difference that the discharge current in the former is substantially higher at cathodic potentials in the presence of N2O. This effect is presumably caused by an autoelectron emission of electrons from nanotubes into electrolyte.