Electrochemical reduction of derivatives and isomers of ethylpicolinate

Electrolysis of picolinic acid, 2-formylpyridine, 2-hydroxymethylpyridine, ethylnicotinate and ethylisonicotinate in aqueous sulfuric acid solutions was performed on a lead cathode in galvanostatic mode. Electrolyses of picolinic acid, ethylnicotinate and ethylisonicotinate were performed in aqueous solutions to prepare the different hydroxymethylpyridine isomers. Results were compared with those for ethylpicolinate: the chemical yield in 2-hydroxymethylpyridine is lower than that in 3-hydroxymethylpyridine while that in 4-hydroxymethylpyridine is better. Electrolyses of the intermediates 2-formylpyridine and 2-hydroxymethylpyridine in aqueous solutions were performed with a view to understanding the competition between the reduction of the side chain and that of the pyridine nucleus. Study of medium acidity, current density, concentration and temperature shows that electroreduction occurs on the pyridinic nucleus of the formylpyridine and the picoline principally and less on the other derivatives.     

Electrochemical reduction of nitrate in weakly alkaline solutions

The electrocatalytic activity of several materials for the nitrate reduction reaction was studied by cyclic voltammetry on a rotating ring disc electrode in solutions with different concentrations of sodium bicarbonate. Copper exhibited highest catalytic activity among the materials studied. Nitrate reduction on copper was characterized by two cathodic shoulders on the polarization curve in the potential region of the commencement of hydrogen evolution. In this potential range an anodic current response was observed on the Pt ring electrode identified as nitrite to nitrate oxidation. This indicates that nitrite is an intermediate product during nitrate reduction. These conclusions were verified by batch electrolysis using a plate electrode electrochemical cell. Copper and nickel, materials representing the opposite ends of the electrocatalytic activity spectra, were used in batch electrolysis testing.     

Study of the hypophosphite effect on the electrochemical reduction of nitrobenzene on Ni

The effect of the hypophosphite ion on the electrochemical reduction of nitrobenzene on Ni was evaluated from a cyclic voltammetric study and from constant potential electrolysis in an aqueous-ethanol alkaline medium. The results were compared with the data obtained in an hypophosphite-free solution. It was found that in an hypophosphite containing solution an unusual selective reduction of nitrobenzene to nitrosobenzene occurs. It is the first time that nitrosobenzene is detected as the reaction product of the nitrobenzene electrochemical reduction in an aqueous-ethanol solution. It is proposed that the Ni modified surface which is formed upon hypophosphite oxidation is responsible for the non reducibility of nitrosobenzene. The effect of the electrode potential on the nitrobenzene electrolysis on a Ni modified electrode was analysed. It was concluded that the highest nitrosobenzene yield (33%) and selectivity (82%) is achieved at −1.1 V. It was also found that the formation of nitrosobenzene leads to an electrode poisoning effect in the electrolysis process.     

Electrolytic reduction of 3-cyanoquinoline

Two well-defined one-electron waves are observed on the polarograms for the reduction of 3-cyanoquinoline in 95% ethanol containing 1M ammonium acetate. During macroscale electrolysis at a potential on the plateau of either wave, the ratio of the wave-heights remains unity. Polarographic and voltammetric evidence is presented for a mechanism in which the first wave represents a reversible one-electron reduction to a radical which then rapidly dimerizes. The second wave represents an irreversible one-electron reduction of the initially formed radical. The reduction mechanism suggested by the electrochemical evidenceis verified by the isolation of dimeric products from controlled-potential electrolysis at the top of the first wave and the isolation of 1,4-dihydro-3-cyanoquinoline at the top of the second wave. The chemical characteristics of the dimeric products and the two-electron reaction product are discussed.     

降低金属阳极电解生产工序电耗的措施

介绍了为降低电解工序的电耗所采取的包括电解厂房设计,合理选用电槽、隔膜、导板,加强电槽管理等措施。     

Cathodic reduction of cinnamoyl chloride

The electrolysis of cinnamoyl chloride in dry acetone anhydrous lithium perchlorate is carried out under controlled cathodic potential on a preparative scale. The ketonic reaction products are identified and their formation is rationalized through the electrogeneration of cinnamoyl free radical, hydrogen abstraction and dimerization of the aldoketene intermediate.     

Cathodic reduction of phenacyl bromide

The cathodic reduction of phenacyl bromide yield different products when the electrolysis is carried out in dimethylformamide or methanol. The formation of products is rationalized.     

Galvanostatic electrochemical reduction of pentoses

Electrochemical reduction of ribose and xylose has been studied in sodium sulphate solution and in phosphate buffers on amalgamated lead cathodes under conditions of galvanostatic electrolysis. The products after peracetylation were determined by gas chromatography. Over the catholyte pH range 8–11 high yields of the pentitols were obtained (84 and 75% for ribose and xylose, respectively). Regardless of the pH, 2-deoxypentitols were also formed in low yields (a few percent). Raising the temperature of the reaction to 45°C intensified the reduction 2 to 3 fold and, with xylose, the yield of xylitol was markedly increased. Large differences were observed between pH readings in the bulk solution and at the cathode. In unbuffered solutions these differences enhanced the rate of reduction of the pentoses autocatalytically.     

Electrochemical reduction of tetraphenylcyclopentadienones

The electroreduction behavior of tetraphenylcyclopentadienone (tetracyclone) and some of its m,m′-and p,p′-substituted derivatives in acetonitrile was investigated. The mechanism for the electroreduction of these compounds in the absence and in the presence of protons was proposed using the results of cyclic voltammetry and controlled potential electrolysis experiments. The effects of the substitution on the peak potentials and on the stability of the anion radicals are discussed.     

Oxygen reduction electrodes for electrolysis in chlor-alkali cells

Oxygen reduction electrodes, containing non-noble metal catalysts supported on high surface area carbon and wet-proofed with PTFE were tested under reaction conditions for the chlor-alkali electrolysis. Double-layer gas diffusion electrodes were prepared by rolling of an active layer and diffusion layer on a nickel wire screen, compressed and sintered at 300 °C. Electrochemical measurements for substantiating the activity and stability of the half-cells were conducted in 8 M NaOH by supplying oxygen at a cell temperature of 70 °C and a constant current load of 300 mA cm⁻². An electrolysis cell with a dimensionally stable anode (DSA) and double-layered cathode was assembled, where 4.8 M NaCl and oxygen were supplied, respectively, for the production of chlorine and NaOH. The cell performances as well as stability of the electrodes were investigated at about 80 °C. This study shows that by replacing the high voltage consuming hydrogen-evolving reaction and by adopting highly active electrocatalysts as cathode materials, energy savings of more than 30% could be realized.     

The autoprotonation in reduction mechanism of pesticide ioxynil

The reduction mechanism of ioxynil (3,5-diiodo-4-hydroxy-benzonitrile) was studied in dimethylsulfoxide using the electrochemical methods (tast polarography, cyclic voltammetry and controlled potential electrolysis) combined with GC/MS identification of products. The reduction is accompanied by the cleavage of iodide yielding 3-iodo-4-hydroxybenzonitrile. Surprisingly, this process requires only one electron for the exhaustive electrolysis of the starting compound. We showed that the apparent one electron reduction observed in the aprotic solvent is due to the autoprotonation by another molecule of ioxynil. The overall one electron reduction (uptake of two electrons per two molecules of ioxynil) is changed in the presence of a strong proton donor to a two electron process per one molecule.     

Electrochemical reduction of silicon chloride in a non-aqueous solvent

The electrodeposition of silicon was engaged in propylene carbonate containing SiCl₄ and tetrabutylammonium chloride. Cyclic voltammograms showed the possibility of electrodeposition of Si at −3.6 V versus Pt quasi-R.E. Potentiostatic electrolysis yielded a porous and white deposit with the thickness of 50 μm at −3.6 V for 1 h. Raman spectroscopic analysis of the deposit immersed in pure propylene carbonate soon after the electrolysis confirmed that the electrodeposit was amorphous silicon. Moreover, EDX and XPS results indicated that the electrodeposited Si was so active that it was oxidized immediately in the air. Finally, the electrodeposition process of Si film is discussed based on chronopotentiometry and chronoamperometry.     

电解系统降低杂散电流腐蚀的设计

介绍了氯碱工业电解系统杂散电流的产生及特点，以及为降低或杜绝杂散电流的腐蚀作用在设计工作中的思路和措施。     

硝基苯电还原制备对氨基苯酚工艺过程

采用固定床电解槽还原硝基苯制备对氨基苯酚,并对其工艺条件进行了优化。以铜网组成固定床电解槽阴极,镀铱钛网(DSA)作为阳极,在电流密度为1000 A·m^-2,阴极电解槽内流速为4.28 cm·s^-1,铜网厚度为10 mm,温度为85℃条件下,硝基苯还原的电流效率接近100%,对氨基苯酚的选择性可达到83%。电解液可循环套用5次,硫酸和氨水的消耗量降至原来的25%,硫酸铵和废水的排放量也减少了75%。采用扩散渗析法回收废弃电解液中的硫酸,以APS为阴离子交换膜,模拟液的流量为0.01 ml·min^-1、温度为20℃时,酸回收率达到61%,且对氨基苯酚和苯胺的透过率分别仅为1.4%和1.6%。     

Electrochemical reduction processes in indigo dyeing

The application of indirect electrolysis as a reduction technique in indigo dyeing is described. Various reversible redox systems were tested to determine whether they are suitable for indigo dyeing. The results of the dyeing trials confirm that the process engineering involved can be applied to the production of denim. The new process offers environmental benefits and offers the prospects of improved process stability, because the reduction state in the dyebath can be readily monitored by measuring reduction potential.     

X-ray photoelectron spectroscopy study of sodium reactions in carbon cathode blocks of aluminium oxide reduction cells

Aluminium oxide reduction was performed in a laboratory electrolysis cell with different industrial carbon cathode blocks (semi-graphitic, graphitic, and graphitized blocks). During electrolysis, sodium species migrate from the bath into the carbon cathode. Consequences of this migration include expansion of the blocks—the so-called sodium swelling—that may lead to failure of the cell. Characterisation of the blocks by XPS indicated that in addition to ionic sodium species (e.g. NaF and NaHCO₃), two different types of metallic sodium were present in the cathodes. One type of metallic sodium is associated with a degradation of the graphitic structure, suggesting that this sodium is intercalated between the graphene layers, whereas the other type of metallic sodium was most probably present in micropores. Both types of metallic sodium were detected in semi-graphitic blocks while only the “micropore” sodium was found in graphitic and graphitized blocks. The metallic sodium was remarkably stable in the laboratory atmosphere, probably due to the fact that, after electrolysis, the entire porosity of the carbon cathode is filled with penetrated bath. This limits the access of oxygen and humidity to the metallic sodium.     

Homolytic reduction of onium salts

Onium salts have proved to be efficient sources of carbon-centered radicals. They can undergo homolytic reduction by single electron transfer (SET) and participate in subsequent synthetic transformations. This review aims to provide an overview on the behavior of onium salts including diazonium, sulfonium, selenonium, telluronium, phosphonium and iodonium cations toward various reductive methods such as radiolysis, electrolysis, photolysis or the use of SET reagents. Mechanistic and synthetic aspects are presented. Applications in polymers and materials science are not covered.     

Chlorate formation and reduction in undivided hypochlorite cells

The accumulation of chlorate in a recirculating undivided brine electrolysis cell is followed. A variety of cathode materials were used and it is apparent that cathodic reduction of the ClO₃ ion takes place. This reaction appears to be activation-controlled.     

Electrochemical reduction of cerium oxide into metal

The Fray Farthing and Chen (FFC) and Ono and Suzuki (OS) processes were developed for the reduction of titanium oxide to titanium metal by electrolysis in high temperature molten alkali chloride salts. The possible transposition to CeO₂ reduction is considered in this study. Present work clarifies, by electro-analytical techniques, the reduction pathway leading to the metal. The reduction of CeO₂ into metal was feasible via an indirect mechanism. Electrolyses on 10 g of CeO₂ were carried out to evaluate the electrochemical process efficiency. Ca metal is electrodeposited at the cathode from CaCl₂–KCl solvent and reacts chemically with ceria to form not only metallic cerium, but also cerium oxychloride.     

电化学耦合阴极二氧化碳还原与阳极氧化合成

电催化二氧化碳还原（CO₂RR）利用电场作用在温和的条件下将二氧化碳转化为高值化学品。将CO₂RR与热力学电势较低的阳极反应耦合,可以降低槽电压,在阳极和阴极同时生成高值化学品,提高能量效率。本文介绍了CO₂RR与氧化合成反应耦合策略,探究了电解池、离子交换膜等电解装置对CO₂RR耦合电催化性能的影响,归纳了常用于CO₂RR耦合氧化合成体系中阴阳极电催化剂的种类,重点综述了CO₂RR与氯碱过程、醇类和含氮有机物氧化等典型阳极氧化合成反应耦合的最新进展。最后,针对目前存在的阳极催化剂成本高、全电解阳极产物的分离检测困难、反应物转化率低等问题,提出开发更加高效、稳定和低成本的阳极电催化剂、升级电极结构和电解装置以及拓展新型CO₂RR耦合体系等是未来的研究方向。