PART 2. ELECTROSYNTHESIS

Several types of electroanalytical techniques may be used to gain knowledge concerning the reaction mechanism of an electrolytic reaction and to determine the optimal conditions for an electrosynthesis. The use of classical polarography was illustrated in part I.1 The different electroanalytical techniques have been treated comprehensively in a monograph,9 and the use of... 

Electrosynthesis is useful when the electrode reaction is stereo specific. For example, for a,a -dibromosuccinic acids, the threo form of both the free acid and its anions is reduced to fumaric acid. On the contrary, the erythro epimer is reduced to fumaric acid only in the undissociated form and as a dibasic anion. The univalent anion is at least partly reduced to maleic acid. Both threo and erythro epimers of dialkyl esters of dibro-mosuccinic acid are reduced, similarly to the undissociated free acids, to only the dialkyl ester of fumaric acid (134,135). 

Apart from the technical aspects, the general conditions for implementing an electrosynthesis are of critical importance. The prospects of the process increase when the project forms part of an important operation of the company or serves its strategic aims. The situation with intermediates, the company s own experience with electro-syntheses, and possible alternative processes will also influence the decision. 

Alvarez-Gallegos A, Pletcher D. The removal of low level organics via hydrogen peroxide formed in a reticulated vitreous cathode cell Part 1. The electrosynthesis of hydrogen peroxide in aqueous acidic solutions. Electro-chim Acta 1998 44 853-861. 

As to the downside of electrosynthesis, when a company considers a new synthesis, one may have to admit that organic synthesis is a huge edifice and electroorganic reactions, as known so far, are a small part of the whole. One of the reasons for this is that the ratio of organic chemists to electro-organic chemists in the United States is more than 10 1. 

Markle, W. Speiser, B. Tittel, C. Vollmer, M., Combinatorial micro electrochemistry - part 1. Automated micro electrosynthesis of iminoquinol ether and [1,2,4]triazolo[4,3-alpha] pyridinium perchlorate collections in the wells of microtiter plates, Electrochim. Acta 2005, 50, 2753-2762... 

In the second part, we want to report some significant procedures of electrosynthesis, carried out in RTILs as well as in VOC-supporting electrolyte systems, including a comparison between the results obtained according to the two different procedures. The synthesis of P-lactams, the utilization of CO as renewable carbon source and the carbon-carbon bond formation via umpolung of aldehydes (benzoin condensation, Stetter reaction) and via Hemy reaction have been selected as typical procedures. 

J. H. P. Utley and C. Z. Smith. Electroorganic reactions. Part 53. The electrosynthesis of novel water-soluble poly-(p-xylylene)(PPX) and poly(p-phenylenevinylene)(PPV) polymers and co-polymers. J. Mater. Chem., 10 2642-2646, 2000. 

C. Belmont, H. H. Girault, Coplanar interdigitated band electrodes for electrosynthesis Part 2. Methoxylation of furan, J. Appl. Electrochem., 1994, 24, 719-724. 

R. Ferrigno, J. Josserand, V, P. F. Brevet, F[. F[. Girault, Coplanar interdigitated band electrodes for electrosynthesis. Part 5. Finite element simulation of paired reactions, Electrochim. Acta, 1998, 44, 587-595. 

S. Rode, A. Attour, F. Lapicque, M. Madosz, A thin-gap single-pass high conversion reactor for organic electrosynthesis. Part 1 model development, J. Electrochem. Soc., 2008, 155. E193-E200. 

It can be seen that the Involvement of free radicals in the Kolbe electrosynthesis is actually not the question. Rather, it is whether these radicals are free to react homogeneously in solution —although formed by a concerted electron transfer/decarboxylation process at the electrode surface—or are adsorbed In an excellent review of the anodic reactions of carboxylates, Utley " has presented a reaction scheme (shown in part below) which is adequate for most purposes. In a concluding section of this review, the question of free radical intermediates vis a vis adsorbed radicals is discussed in considerable detail. However, it would seem that the only conclusion one can draw is that the mechanism of this electro-organic process is still by no means settled. However, the following steps are likely to be involved ... 

Despite all these advantages, alternative chemical methods of synthesis are being developed and improved [19-25] that will partly take the place of electrosynthesis, even for electrochemical applications such as batteries and sensors. This is associated in part with the great difficulties in correlating the properties of the material with the conditions of synthesis. This is a consequence of the complexity of electrochemical synthesis, which involves different experimental variables, both chemical (nature of the solvent, the monomer, and the dopant salt) and physical (temperature, electrical conditions, nature and shape of the electrodes, geometry of the cell). In addition, the effects of all these variables are interdependent. As a consequence, adequate control of polymer electrosynthesis, and hence of the polymer properties, will require analysis of the effects of the individual parameters and their reciprocal dependence. This will be the objective of the first part of the chapter. 

Although organic electrosynthesis is only a small part of electrochemistry, recounting its history chronologically and in detail would take more time than is allotted to this presentation and in any event would serve no useful purpose. The author will therefore pick out the important milestones on the way to the relative sophistication we enjoy today in designing and carrying out organic electrosyntheses. These landmarks are usually associated with scientists names so this will be an opportunity for those not previously acquainted with this field to learn at least the names of those responsible for major advances. 

Fleischmann, M., Tennakoon, L., Bampfield, A. and WiUiams, P.J. (1983) Electrosynthesis in systems of two immiscible liquids and a phase transfer catalyst, part 111. Characterisation of thin film contactor cells characterisation of thin film contactor cells. Journal of Applied... 

Electron-transfer reactions in nitrogen fixation. Part 1. The electrosynthesis of dinitrogen, hydride, isocyanide, and carbonyl complexes of molybdenum intermediates, mechanisms, and energetics... 

Pickett, C.J., Ryder, K.S. and Talarmin, J. Electron-transfer reactions in nitrogen fixation. Part 2. The electrosynthesis of ammonia Identification and estimation of products... 

Fauvarque JF, Jutand A, Francois M (1988) Nickel catalysed electrosynthesis of anti-inflammatory agents part I - synthesis of 2-arylpropanoic acids, under galvanostatic conditions. J Appl Electrochem... 

More than 10 years after the establishment of the acetalization process, electrochemists at BASF have searched for a compatible reductive process that can be run instead of the hydrogen evolution. What they have found is the reduction of phthalic acid dimethylester to phthalide [8] (Fig. 2). Phthalide is a compound that was up till then generated by classical catalytic hydrogenation from phthalic acid anhydride [7]. Part of the process development has been to fit the paired electrosynthesis in the same capillary gap cell like the acetalization of the toluene derivatives. 

Future directions, respectively, particular processes, are hard to foresee though the development of more paired electrosynthesis examples is being expected because the essence of such an electrolysis is very attractive it uses the mole of charge moved in the cell in the most efficient way. The work can be based on the knowledge about successful paired electrosyntheses that is generated for decades as it is partly reflected by the presented examples. 

In spite of all these advantages, the electrogeneration of polypyrrole is losing interest as a method for obtaining these materials. Alternative chemical methods of synthesis are being developed partly taking the place of electrosynthesis, even for such electrochemical... 

Tomilov took an active part in organizing and holding EKhOS conferences he wrote several monographs on organic electrosynthesis in collaboration with Fioshin, S. Mairanovskii, and Smirnov. Some of the episodes from the scientific and organizational activities and memories of meetings with scientists are presented in his book [89]. 

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