Electrochemistry cathodic reduction

In spite of the high effort focused on the carbon electrochemistry, very little is known about the electrochemical preparation of carbon itself. This challenging idea appeared in the early 1970s in connection with the cathodic reduction of poly(tetrafluoroethylene) (PTFE) and some other perfluorin-ated polymers. The standard potential of the hypothetical reduction of PTFE to elemental carbon ... 

The trapping of hydroxyl radicals has also been of interest in connection with electrochemistry. Bard et al. (1974) initiated electrochemical applications of spin trapping and showed, for example, that the cathodic reduction of diazonium salts in the presence of PBN gives aryl-radical spin adducts. A route... 

Heterocycles are of great interest in organic chemistry due to their specific properties. Many of these cycles are widely present in natural and pharmaceutical compounds. Electrochemistry appears as a powerful tool for the preparation and the functionalization of various heterocycles because anodic oxidations and cathodic reductions allow the selective preparation of highly reactive intermediates (radicals, radical ions, cations, anions, and electrophilic and nucleophilic groups). In this way, the electrochemical technique can be used as a key step for the synthesis of complex molecules containing heterocycles. A review of the electrolysis of heterocyclic compounds is summarized in Ref. [1]. 

E and E, . represent the equilibrium potential of mineral anodic dissolution and cathode reduction of oxygen, respectively. represents the mineral mixed potential in certain system. and Zg are current density of anodic and cathode reaction, respectively. When the discharge is the controlled step of electrode reaction, according to electrochemistry theory, the equation can be described as following ... 

Electrochemistry offers alternative routes to the preparation of active zinc for the Reformatsky reactions, for instance exploiting the cathodic reduction (—0.8 V v.v SCE) of ZnBr2 in acetonitrile containing Bu4N+BF4 as supporting electrolyte53. 

Cathodic reduction of oxygen is the most convenient method of production of the superoxide radical-anion,. The properties of this important species have been well reviewed and key references to the extensive work on the electrochemistry of oxygen are contained therein. Of immediate significance is the large cathodic shift in E° for the 0 /0 couple which accompanies a change from aqueous to aprotic solvent (e.g. DMF, DMSO, and MeCN) this is interpreted in terms of relatively weak solvation in aprotic media which enhances the nucleophilicity of the superoxide anion. However, in the presence of acids the chemistry of superoxide is dominated by the disproportionation shown in equation 1. 

This review describes the electrochemical behavior of compounds containing the C=C, C=0 and C=N functional group. The review covers both anodic oxidation and cathodic reduction of such compounds. The electrochemistry of these functionalities was reviewed in an earlier volume of this series1 this article updates the previous one but does not include the material included there. The Kolbe oxidation of carboxylic acids has... 

The cathodic reductions of nitro compounds are among the most thoroughly investigated reactions of organic electrochemistry. At least on the laboratory scale, the reaction permits the synthesis of many intermediates with different oxidation states. However, most syntheses can now also be carried out more economically by catalytic reactions. Therefore, only a few electrochemical reactions are still of industrial interest, i.e. the single-step syntheses of hydroxylamines, aminophenols, or anisidines. 

Scaling up a reaction in the laboratory often presents unexpected problems, and probably every organic chemist has experience of this. With the recent development of continuously operating cells (Sect. 6.2) a fairly small device should easily handle large quantities of electrolyte and hence provide an attractive alternative to any chemical method. As an example, dissolving metal reductions, notoriously difficult and sometimes expensive to run on a large scale, could preferably be replaced by cathodic reductions in many cases. A recent survey of electrochemistry in Britain has produced a list of reactions, which deserve consideration from the industrial point of view 39 ... 

Similarly, cations of common use in organic electrochemistry can be ordered according to their resistance towards cathodic reduction, viz.,... 

Selective cathodic reduction of pyridines is a process of great industrial significanee [171]. As an example, dimethyl pyridinedicarboxylates undergo a highly selective electroreduction in methanol by use of a divided cell. The product obtained depends on the position of the substituents. Thus, the 2,3- and 2,5-dicarboxylates give the 1,2-dihydropyridines whereas the 2,6-, 3,4- and 2,4-dicarboxylates the 1,4-dihydropyridines [172]. Many other ring reductions of azines (often with dimerization as a side-reaction, see Section 6.4.3) are discussed in electrochemistry texts and reviews [116]. Attempts have been made to rationalize the herbicidal properties of dipyridinium salts in terms of their cathodic behavior [173]. 

Historically, cathodic reduction was one of the first subjects explored in the area of organofluorine electrochemistry. PerfluoroaUcyl halides are reduced cathodically much easier than the corresponding... 

In many cases electrochemistry proved to be a powerful tool to activate the SnAt reactions. The cathodic reduction in aromatic compounds, prior to their interaction with nucleophilic reagents, is a new essential step of the S Ar reactions. Moreover, a basic thermodynamic study explains (BDEs values of C-Nu vs. C-H), why F, OH, OR, and SR nucleophiles do not react with arenes or heteroarenes. 

In 1898, in a study of the cathodic reduction of nitrobenzene, Haber discovered that by varying the electrode potential he could obtain either azoxybenzene or hydrazobenzene. This led him to make the following significant conclusions The electric current up to this time has been regarded in organic electrochemistry as a... 

One of the strengths of organic electrochemistry is its variety. Already in a simple beaker-type cell connected to a rectifier, one can conduct cotmtless different electrolyses anodic oxidations as well as cathodic reductions. The reactions are as manifold as chemistry itself is manifold thinking only about one of the oldest organic syntheses the Kolbe electrolysis [1] that is utilized till today [2,3] or the versatile anodic substitution [4] or the... 

Lund, H., 1991, Cathodic reduction of nitro and related compounds, in Organic Electrochemistry, an Introduction and a Guide, (Henning Lund and M. M. Baizer, eds.), Marcel Dekker, New York, pp. 401-432. 

The cathodic reduction of dissolved oxygen to peroxide was first demonstrated by Traube in 1882. Commercialization of an electrolytic process for hydrogen peroxide has been retarded by several factors related to the complex electrochemistry of oxygen reduction, together with a poor understanding of the influence of electrode materials and cell design on the process efficiency. There has been a gradual awareness of the desirable factors for a successful process over the last 10-15 years, which include ... 

So, any reaction that favors the consumption of Na20 or SO3 will lead to the dissociation of Na2S04 and vice versa. Molten Na2S04 is an ionic conductor the hot corrosion mechanism should generally be electrochemistry [78]. In other words, hot corrosion itself is an electrochemical process that includes anodic oxidation, cathodic reduction and ion diffusioa As for the hot corrosion of Ti3AlC2, the anodic oxidation process mainly consists of the anodic dissolution of Ti and Al ... 

It must be noted that impurities in the ionic liquids can have a profound impact on the potential limits and the corresponding electrochemical window. During the synthesis of many of the non-haloaluminate ionic liquids, residual halide and water may remain in the final product [13]. Halide ions (Cl , Br , I ) are more easily oxidized than the fluorine-containing anions used in most non-haloaluminate ionic liquids. Consequently, the observed anodic potential limit can be appreciably reduced if significant concentrations of halide ions are present. Contamination of an ionic liquid with significant amounts of water can affect both the anodic and the cathodic potential limits, as water can be both reduced and oxidized in the potential limits of many ionic liquids. Recent work by Schroder et al. demonstrated considerable reduction in both the anodic and cathodic limits of several ionic liquids upon the addition of 3 % water (by weight) [14]. For example, the electrochemical window of dry [BMIM][BF4] was found to be 4.10 V, while that for the ionic liquid with 3 % water by weight was reduced to 1.95 V. In addition to its electrochemistry, water can react with the ionic liquid components (especially anions) to produce products... 

---