Electro-Organic Methods

Discoveries of new types of electro-organic reactions based on coupling and substitution reactions, cyclization and elimination reactions, electrochemically promoted rearrangements, recent advances in selective electrochemical fluorination, electrochemical versions of the classical synthetic reactions, and successful use of these reactions in multistep targeted synthesis allow the synthetic chemist to consider electrochemical methods as one of the powerful tools of organic synthesis. 

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The selective oxidative phenolic orf/io-coupling reaction of simple methyl-substituted phenols turned out to be challenging [12]. When 2,4-dime thy Iphenol (1) is treated by conventional or electro-organic methods, not only the desired biphenol (2) is formed but rather a plethora of polycyclic architectures (Scheme 2) is observed. The major product is Pummerer s ketone (3) and related compounds with a wide structural diversity [13-16]. Application of a boron tether ameliorated the situation tremendously, and biphenol (2) was obtained as the major product [17, 18]. This templated anodic oxidation of 1 represents a multistep process but is suitable for the electro-organic synthesis of (2) on larger scale (see entry Electrosynthesis Using Template-Directed Methods ) [19]. 

For the organic chemist, product studies in the widest sense, ie., including stereochemical aspects, isotope effects, etc. fall most natural in the study of electro-organic reactions. However, there are also some simple electrochemical techniques which are extremely useful in the design of electrochemical syntheses and can be set up in any laboratory for a modest cost. These methods — which are the ones to be discussed here - include different kinds of voltammetry, controlled potential electrolysis, and coulometry, andigive information as to the nature of the electro-active species, the possible nature of intermediates involved and their reactions with reagents present, and the number of electrons involved in the process. 

In 2000, about 110 chemicals were being produced by electro-organic syntheses at a rate of more than 10,000 tons/year. The best-known method has already been presented in this chapter (Section 11.2.3) it is the electro-hydrodimerization of acrylonitrile to adiponitrile as part of the synthesis of nylon. 

Fig. 19.3 Scheme of an open and undivided Pt/02 cell of 100 cm3 capacity with an ( -diffusion cathode used for the degradation of organic pollutants by indirect electro-oxidation methods with Pt, BDD, and Fe anodes (Brillas et al. 1995)... 

It has been shown that indirect electro-oxidation methods based on H2O2 electrogeneration such as electro-Fenton, photoelectro-Fenton, and peroxi-coagulation are promising techniques for an effective and efficient decontamination of acidic wastewaters containing persistent organic pollutants. They are environmentally... 

Refs. [i]KahlertH (2002) Reference electrodes. In ScholzF (ed) Electro-analytical methods. Springer, Berlin, pp 261-277 [ii] Ives DJG, Janz GJ (1961) Reference electrodes. Academic Press, New York [Hi] Bard A, Faulkner LR (2001) Electrochemical methods, 2nd edn. Wiley, New York, pp 24-28 [iv] Parsons G (1974) Pure Appl Chem 37 503 [v] Inzelt G (2006) Standard potentials. In Bard AJ, Stratman M, Scholz F, Pickett CJ (eds) Inorganic electrochemistry. Encyclopedia of electrochemistry, vol. 7A. Wiley-VCH, Weinheim, p 1 [vi] Lund H (1983) Reference electrodes. In Baizer MM, Lund H (eds) Organic electrochemistry. Marcel Dekker, New York, chap 5 V, pp 187-191 [vii] Gritzner G, Kuta J (1984) Pure Appl Chem 56 461 [viii] Dohos D (1975) Electrochemical data. Akadimiai Kiadd, Budapest... 

Baizer has critically reviewed the prospects for further application of organic electrosynthesis and has compiled a list of conditions for the successful use of this technique. The main suggestions were use of electrochemical methods in oxidation or reduction processes, where stoichiometric concentrations of oxidants or reductants, especially exotic ones, cf. Refs. 33,770,806) needed in conventional synthesis the use of an electro-organic syntheris where it is the only successful approach finally in small-scale processes, e.g. the production of medicinals or fine chemicals. These and further suggestions may be found in Refs. 33,754,769.770) p j. further information, concerning other examples of electro-synthesis, the reader is referred to recent reviews published by Lelandais Fioshin Baizer Koster... 

Torii, S. Electro-organic Syntheses, Methods and Applications, Part I Oxidations VCH Weinheim, Germany, 1985 Chapter 11. 

S. Torii, Electro-Organic Syntheses Methods and Applications, Kodansha, Tokyo, 1985. 

Cheng, X.-M., S.-W. Yao, C.-Q. Li, T. Manaka, and M. Iwamoto. 2004. Measurement of surface potential at metal/organic-material interfaces by electro-absorption method. Chin Phys Lett 21 2026. 

In a later section (Section 8), some of the fundamental aspects of polarography will be briefly considered with particular reference to the question of reversibility of various electro-organic reactions studied by means of polarography. Finally, an attempt will be made to discuss those techniques complementary to the basic polarographic method, but essential for any deductions regarding the nature of intermediates and products in an organic electrode reaction, and therefore regarding its overall reaction mechanism. 

Polarographic Methods and Related Techniques for the Study of Electro-Organic Reactions... 

II. EXPERIMENTAL METHODS FOR ELUCIDATION OF MECHANISMS OF ELECTRO-ORGANIC OXIDATION... 

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