A possibility of using metal complexes with redox-active ligands in organic electrosynthesis is demonstrated on the basis of literature data analysis. Unlike homogeneous catalysis, many examples are known for the application of complexes of this type in electrocatalytic processes characterized by a higher selectivity and milder conditions. Interest in metal complexes with redox-active ligands is due to their use in the heterogeneous electrocatalysis as well. The main attention is given to advantages of the indirect electrosynthesis of organic compounds, in particular, sulfur derivatives, in the presence of mediators or electrocatalysts based on metal complexes with redox-active ligands. Active forms of metal complexes are generated at the electrodes and can initiate the further transformations of inert substrates. A significant decrease in power expenses compared to the direct redox activation of reagents is the main advantage of indirect electrosynthesis. The cyclic processes favoring a permanent regeneration of metal complexes lead to an increase in the yield of target compounds.

The removal of acidic sulfur-containing components [hydrogen sulfide (H2S) and alkanethiols or thiols (RSH)] from simulated mixtures and analogues of gasoline fractions with Zn(II), Cu(II), Co(II), and Ni(II) acetates, pivalates, and malonates applied on silica gel with various porosities under ultrasonic treatment in solution has been studied. The dependence of the adsorption of H2S and RSH on the surface of silica gel modified by metal complexes with organic ligands on various factors (the pore size of the silica gel, the time of ultrasonic treatment, and the nature of carboxylate complexes) is established. The best results for the removal of total sulfur from the model mixture and an analogue of the gasoline fraction were obtained using silica gel modified with zinc pivalate (96%) and cobalt pivalate (95%). A waste-free method to desulfurize fuel with zinc pivalate based on the production of practically useful ZnS is suggested.

Reactions of electrochemically generated antimony(V) and tin(IV) complex species containing a tridentate O,N,O-donor ligand with various thiols were studied. Among main group metal complexes with N,N-bis(2-hydroxy-di-3,5-tert-butylphenyl)amine (CatH2–NH–CatH2), compounds [Me2Sn(Cat-N-SQ)] (I), [Et2Sn(Cat-N-SQ)] (II), [Ph2Sn(Cat-N-SQ)] (III), [(c-C6H11)2Sb(Cat-N-Cat)] (IV), and [Ph3Sb(Cat-NH-Cat)] (V) are the most active, able to mediate the oxidation of thiols (1-hexanethiol, cyclohexanethiol, and 4-methoxythiophenol), to symmetrical disulfides were identified. The anodic activation of Sb(V) and Sn(IV) complexes involves organic ligands and gives rise to intermediates that react with thiols. During the mediated electrosynthesis, the initial complex species is regenerated in solution. The use of metal complex mediators decreases the anodic overvoltage of the thiol oxidation in comparison with direct electrochemical synthesis. The yields of products depend on complex and thiol structures or ratio. The highest efficiency in the electrocatalytic reactions was found for the [Ph3Sb(Cat-NH-Cat)] complex, which should be used for the synthesis of disulfides.

A logical-informational model of energy resource-efficient chemical technology for the utilization of hydrogen sulfide and low molecular alkanethiols, which are toxic and difficult to remove sulfur components of residual fuel (fuel oil), is proposed. Based on the IDEF1 methodology and existing knowledge about the technological processes of the demercaptanization of various hydrocarbon raw materials (oils, gas condensates), a scheme for the production of organic sulfur compounds from sulfur waste extracted from fuel oil has been modeled. For a sufficiently complete removal of hydrogen sulfide and low molecular weight alkanethiols, energy- and resource-saving stages of the technological process have been developed, which are implemented by ultrasonic and/or magnetic treatment of fuel oil. It is proposed to use the combined action of two alternative methods of processing fuel oil to increase the efficiency of cleaning fuel oil from sulfur components. For the first time, an approach has been developed to utilize unwanted sulfuric impurities contained in fuel oil by involving electric and microwave synthesis in green technological processes, to obtain practically useful organic sulfur compounds with biological activity. It is shown that the use of one-electron oxidant thiols and hydrogen sulfide in organic media leads to the synthesis of organic disulfides and elemental sulfur. Indirect (with the use of mediators) electrosynthesis contributes to the cyclic conduct of the technological process, an increase in efficiency and a decrease in energy consumption compared to the direct (on electrodes) initiation of sulfur components.

A method of synthesis of organic mono-, di-, and polysulfides based on electrochemical reactions of unsubstituted and alkyl–substituted cycloalkanes C5–C8 with di(n-butyl)disulfide (di(tert-butyl)disulfide) and hydrogen sulfide is developed. Three–component electrosynthesis is carried out in methylene chloride under atmospheric pressure, at the room temperature under the conditions of anodic H2S activation to a cation radical fragmented to a proton and a thiyl radical. The suggested approach with application of oxidative conversion initiation allows obtaining asymmetric mono-, disulfides and symmetric disulfides. The yield of biologically active organic sulfur derivatives depends on the electrosynthesis duration, structure of isomeric dibutyl sulfides, alicycle size and saturation degree.

The presence of hydrogen sulfide in fuel oil is a danger, since hydrogen sulfide is concentrated in the gas phase of tanks, vessels and tanks truck that when carrying out operations of drainage-fulness can lead to an excess of its MAC in air and to the creation of explosive mixtures. The concentration of H2S in fuel oil produced at refineries is 20-500 ppm, while its content in commercial fuel is limited to 10 ppm. Analytical methods of definition of concentration of a hydrogen sulfide in oil products are considered. Industrial and promising technologies for reducing H2S in fuel oil, their main merits and demerits are presented. The possibilities of low-energy wave technologies in the refinement of petroleum and oil products and mechanisms of action of ultrasound and constant magnetic field on oil disperse systems are shown. The hydrogen sulfide extracted from fuel oil neither on volumes, nor on concentration can't be used as independent raw materials for processing into elemental sulfur in the Claus process and is a toxic by-product. At the same time, hydrogen sulfide-containing wastes can serve as valuable raw materials for the production of wide range of useful organic compounds (antioxidants, drugs, pesticides, fungi-cides) in electrochemical processes. In processes of low-tonnage chemistry, electrochemical processes are relevant. As a result of anode or cathode activation of a hydrogen sulfide (alkanethiols) at ambient temperature and atmospheric pressure the thiyl (alkylthiyl) radical is formed. Along with products of a thiolation of organic compounds are formed also mono - di - and the trisul-phides having higher biological activity and lower toxiferous in comparison with thiols. The competitiveness of electrosynthesis is very high, it is considered as processes of waste-free production as at the heart of it ecologically focused idea of "green chemistry" is concluded.

A novel and efficient method for the synthesis of biologically active organic di-, tri- and tetrasulfides has been proposed. Different methods of redox activation of sulfur, hydrogen sulfide, and thiols in the reactions with organic compounds have been considered. Electrochemical initiation of the reactions of the mediator–H 2 S–S 8 system with cyclohexane, methylcyclohexane, and benzene has occurred to the formation of polysulfides R 2 S n ( n = 2–4). The application of tetrabutylammonium bromide as a mediator of H 2 S oxidation has allowed to decrease the anodic overpotential of electrosynthesis. Di- and tetrasulfides have been obtained under anodic activation of the cycloalkanethiols (C 5 , C 6 ) or thiophenol in the reaction with sulfur. Electroreduction of S 8 in the presence of the same thiols has favored the formation of di- and trisulfides. The yield and the ratio of the R 5 S n ( n = 2–4) depend on the method of redox activation of the thiolating reagent.

A new effective electrochemical method of producing organic di-, tri- and tetrasulfides (R2Sn (n=2-4)) with participation of H2S, S-8 and cycloalkanes C-5-C-7 in the presence of mediator (n-Bu4NBr) has been developed at room temperature. The activation of H2S mediated by the redox couple Br-/Br center dot in the mixture of S-8 allows to generate simultaneously thiyl and hydropolysulfide radicals leading to formation of polysulfides with different number of sulfur atoms. The mediator decreases the anodic overvoltage of the electrosynthesis of R2Sn, compared to a direct anodic activation of hydrogen sulfide.

Biologically active dicycloalkyl di- and trisulfides were prepared by the reactions of cycloalkanes C-5-C-7 with H2S and S-8 under the anodic (cathodic) activation of hydrogen sulfide. In dichloromethane, the electrochemical activation of H2S in the presence of sulfur can generate sulfur-centered radical intermediates that react with cycloalkanes at room temperature. The current yield of di- and trisulfides depends on the method of redox activation of hydrogen sulfide, the concentration of sulfur, and the time of electrosynthesis. The anodic activation of hydrogen sulfide in the synthesis of dicycloalkyl di- and trisulfides in an excess S-8 is more efficient than the cathodic activation. In the series of cycloalkanes C-5-C-7, the highest yield of sulfur-containing products is observed for cycloheptane.

The electrochemical oxidation of the chromium(III) and indium(III) complexes with 3,6-di-tert-butyl-o-semiquinolate leading to the formation of active monocationic species is studied by cyclic voltammetry. The reactions of the latter with hydrogen sulfide generate the radical cation of H2S, whose fragmentation affords the proton and thiyl radical. These complexes are proposed for the first time as redox mediators for the one-pot thiolation of inert cycloalkanes C6–C8, which decreases the activation energy of hydrogen sulfide compared to that for direct electrochemical oxidation. The major products of cycloalkane functionalization involving H2S are thiols and organic di- and trisulfides. The yield of the synthesized compounds depends on the type of the mediator: the chromium(III) complex exhibits the highest efficiency in the electrocatalytic transformations.

Direct and indirect redox-activation of H2S in the presence of cyclopentene or cyclohexene in MeCN at 25 °C affords the corresponding cycloalkanethiols.

The electrochemical oxidation of the chromium(III) and indium(III) complexes with 3,6-di- tert -butyl- o -semiquinolate leading to the formation of active monocationic species is studied by cyclic voltammetry. The reactions of the latter with hydrogen sulfide generate the radical cation of H 2 S, whose fragmentation affords the proton and thiyl radical. These complexes are proposed for the first time as redox mediators for the one-pot thiolation of inert cycloalkanes C 6 –C 8 , which decreases the activation energy of hydrogen sulfide compared to that for direct electrochemical oxidation. The major products of cycloalkane functionalization involving H 2 S are thiols and organic di- and trisulfides. The yield of the synthesized compounds depends on the type of the mediator: the chromium(III) complex exhibits the highest efficiency in the electrocatalytic transformations.

An indirect electrochemical method for thiolation of cycloalkanes C5–C7 has been suggested. The method is based on a new approach to activation of hydrogen sulfide by redox mediators.