V. P. Gul’tyai

Dimerization and protonation reactions of nitrosonitrobenzenes radical anions

The electrochemical behavior of 2-, 3-, and 4-nitrosonitrobenzenes (NNB) in DMF (with Bu4NClO4 suppoting salt) in the presence and in the absence of different proton donors (water, phenol, benzoic, acetic, chloroacetic, and sulfuric acids) is studied by the methods of cyclic voltammetry, chronoamperometry and also by electrolysis at the controlled potential. The electrochemical reduction of these compounds is shown to preferentially afford either monomeric (N-nitrophenylhydroxylamines) or dimeric (azoxy compounds) products, which is determined by the interplay between reactions of protonation and dimerization of NNB radical anions. The dimerization reactions proceed fast and reversibly to afford the corresponding dimeric dianions with the basicity much higher as compared with NNB radical anions as the result of which the monomeric products are formed in the presence of “strong” proton donors and the dimeric products form in the presence of “weak” proton donors. Like the effective rate of formation of dimeric products, the basicity of radical anions increases in the row 4- < 3- < 2-NNB.

Peculiarities of the mechanism of electroreduction of cinnamic acid in DMF and DMF-H2O mixture

The electrochemical behavior of cinnamic acid (CA) on the cathodes with a high hydrogen overpotential (Hg, glassy carbon, and carbositall) in the aprotic solvent (DMF) and in DMF with additions of H2O or Et4NOH is studied by the methods of polarography, preparative electrolysis, cyclic voltammetry (CVA), coulometry, and chronoammetry. It is found that the mechanism of CA electroreduction is in conflict with the classical notion of the mechanism of electroreduction of α,β-unsaturated carboxyl compounds. It is shown that in the aprotic solution, in contrast to similar carbonyl compounds or ethers, which are the derivatives of organic acids, the products of double-bond hydrogenation, rather than the dimeric compounds, are the only products of CA electroreduction, i.e the presence of carboxyl group changes essentially the direction of electrochemical process. From the data of CVA, it is concluded that stable dimeric associates are present in the DMF solutions in the equilibrium with nondissociated CA.

Electrochemical reduction of N-(2-nitro-4-R-phenyl)pyridinium salts using redox-mediators

Electrochemical reduction of N-(2-nitroaryl)pyridinium chlorides was accomplished in acidic aqueous alcoholic medium in the galvanostatic mode using tin, titanium, vanadium, and iron chlorides as redox-mediators. The use of SnCl2 as a mediator catalyst made it possible to shorten the electrosynthesis time as compared to the direct electroreduction on an electrode and prepare the intramolecular cyclization products, viz., substituted pyrido[1,2-a]benzimidazoles, in high yield. The influence of the mediator nature and its amount, current density, temperature, cathode material, medium acidity, and the substrate structure on the efficiency of reductive heterocyclization of N-(2-nitroaryl)pyridinium salts was studied.

Description of catalyzed and induced (initiated) reactions of organic compounds. Terminology problems

The fundamental differences between catalyzed and induced (initiated) reactions and some terminological problems that exist in this field are considered. In particular, illegitimacy of using terms such as “catalytically induced (initiated) reactions”, “expendable catalystrd, and “catalytic additive” is discussed. For non-catalyzed transformations, including conjugated (in particular, multicomponent) and chain reactions, the term self-developing reaction (SDR) is proposed. The criterion of SDR is a high current yield (electrogeneration) or high quantum yield (photoinitiation) of target products; in the case of chemical induction of SDR, a substantially lower consumption of the inductor than required by the reaction stoichiometry can serve as such criterion.

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 E1/2 = −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.

The main trends in the development of electrochemistry of organic compounds in Russia (based on the materials of the 18th All-Russian Conference “EKHOS-2014”)

The state-of-the-art in the field of electrochemistry of organic compounds in Russia is surveyed briefly based on the materials of the 18th All-Russian Conference on Electrochemistry of Organic Compounds and also on the articles of the present special issue of the Russian Journal of Electrochemistry. The results are compared with the general world-wide state-of-the-art in electrochemistry of organic compounds.

Electrochemical behavior of cinnamic acid associates on carbositall electrode in dimethylformamide in the presence of external proton donors

The electroreduction (ER) of trans-cinnamic acid (CA) and its associates in an aprotic solvent, dimethylformamide (DMF), in the presence of proton donors: weak (H2O) and moderate (acetic acid AcOH) and also with addition of R4NOH (R = Et; Bu) to the CA solution in DMF is studied by the methods of cyclic voltammetry (CVA) and chronoamperometry on a cathode with the high hydrogen overpotential—carbositall. The electrochemical behavior of AcOH in DMF and in the mixture 16% H2O–DMF is examined. The results obtained show that CA associates in DMF can include AcOH (or H2O) molecules to form sufficiently stable mixed associates. The anionic species that appear at the reduction of such associates decompose with abstraction of the original CA, which results in the appearance of inverted, i.e., cathodic peaks at ca. -2.0 V in the anodic CVA branch. A comparative study of methyl cinnamate is carried out under similar conditions on the carbositall electrode. In contrast to CA, the behavior of methyl cinnamate in DMF in the presence of a proton donor (AcOH) corresponds to the classical ER scheme for α,β-unsaturated esters.