Syntheses, electroorganic

Many examples of electroorganic synthesis have been reported and a few are commercial. The first significant commercialization of electroorganic synthesis was the electrohydrodimerization (EHD) of acrylonitrile to adiponitrile, an intermediate for hexamethylenediamine, which is a monomer for nylon. 

The reduction takes place at the cathode with a catholyte composed of aqueous quaternary ammonium salt. The anolyte is sulfuric acid. ions generated at the anode pass through the membrane and neutralize the OH ions generated in the catholyte. Commercial installations are operated by Solutia (spun off from Monsanto), BASF, Asahi Chemical, and Rhodia. Some of these manufacturers have developed undivided cells for this process. 

An example is the oxidation of naphthalene with cerium, which has been demonstrated on a pilot scale [47]. Ce(III) in and aqueous solution of methane-sulfonic add is oxidized to Ce(IV) at the anode. The Ge(IV) reacts with naphthalene in a separate vessel to form naphthoquinone and Ge(III). The aqueous phase containing the methanesuUbnic add and Ge(III) is separated and returned to the electrolytic cell. The naphthoquinone is an intermediate for dyes, agricultural chemicals, and anthraquinone, which is made by a Diels-Alder reaction with butadiene. 

The authors would like to express their gratitude to W.W. Carson and A. von Gotteberg for reading the draft and making their comments. 

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Oxidation and reduction reactions can be carried out usiag reformer hydrogen and oxygen from the air. To decide when electroorganic synthesis is likely to be a viable option for a desired product, some opportunity factors are use of cheaper feedstock elimination of process step(s) or a difficult reaction avoidance of waste disposal, toxic materials, and/or abiUty to recycle reagent and abiUty to obtain products from anode and cathode. 

Electrodes. At least three factors need to be considered ia electrode selection as the technical development of an electroorganic reaction moves from the laboratory cell to the commercial system. First is the selection of the lowest cost form of the conductive material that both produces the desired electrode reactions and possesses stmctural iategrity. Second is the preservation of the active life of the electrodes. The final factor is the conductivity of the electrode material within the context of cell design. An ia-depth discussion of electrode materials for electroorganic synthesis as well as a detailed discussion of the influence of electrode materials on reaction path (electrocatalysis) are available (25,26). A general account of electrodes for iadustrial processes is also available (27). 

Tank Cells. A direct extension of laboratory beaker cells is represented in the use of plate electrodes immersed into a lined, rectangular tank, which may be fitted with a cover for gas collection or vapor control. The tank cell, which is usually undivided, is used in batch or semibatch operations. The tank cell has the attraction of being both simple to design and usually inexpensive. However, it is not the most suitable for large-scale operation or where forced convection is needed. Rotating cylinders or rotating disks have been used to overcome mass-transfer problems in tank cells. An example for electroorganic synthesis is available (46). 

R. D. Litde and N. L. Weinberg, eds., Electroorganic Synthesis, FestschriftforManuelM. Baiter, Marcel Dekker, Inc., New York, 1991. 

S. Torii, ed., EecentA.dvances in Electroorganic Synthesis, Studies in Organic Chemistry 30, Elsevier Science Publishing Co., Inc., New York, 1987. 

The first reported electroorganic synthesis of a sizeable amount of material at a modified electrode, in 1982, was the reduction of 1,2-dihaloalkanes at p-nitrostyrene coated platinum electrodes to give alkenes. The preparation of stilbene was conducted on a 20 pmol scale with reported turnover numbers approaching 1 x 10. The idea of mediated electrochemistry has more frequently been pursued for inorganic electrode reactions, notably the reduction of oxygen which is of eminent importance for fuel cell cathodes Almost 20 contributions on oxygen reduction at modified... 

Schafer HJ (1987) Recent advances in electroorganic synthesis. In Torii S(ed)Proc. Istlntemat. Symposium on Electroorganic Synthesis, Kodansha, Tokyo, p 3... 

As noted earlier, the kinetics of electrochemical processes are inflnenced by the microstractnre of the electrolyte in the electrode boundary layer. This zone is populated by a large number of species, including the solvent, reactants, intermediates, ions, inhibitors, promoters, and imparities. The way in which these species interact with each other is poorly understood. Major improvements in the performance of batteries, electrodeposition systems, and electroorganic synthesis cells, as well as other electrochemical processes, conld be achieved through a detailed understanding of boundaiy layer stracture. 

Stark, W., Kinkel, J., Michel, M., Schmidt-Traub, H., Micro reactor for electroorganic synthesis in the simulated moving bed-reaction and separation environment, Electrochim. Acta 48 (2003) 2889-2896. 

Like inorganic substances, organic substances can be anodicaUy oxidized and/or cathodicaUy reduced. Such reactions are widely used for the synthesis of various organic compounds (electroorganic synthesis). Moreover, they are of importance for the qualitative and qnantitative analysis of organic substances in solutions, as for instance in polarography (see Lund and Baizer, 1991). 

Electroorganic synthesis will be covered in section 4.5.4. It is appropriate, however, to make a reference here to the role of u/s in electroorganic processes. Atobe et al. (2000) have reported the effect of u/s in the reduction of acrylonitrile and mixtures of acrylonitrile and methyl acrylate. The selectivity for adiponitrile in the reduction of acrylonitrile was significantly increased under u/s irradiation with a power intensity over the u/s cavitation threshold ( 600 cm ). This favourable influence of u/s can be attributed to the improved mass transfer of acrylonitrile to the electrode interface by the cavitational high-speed jet-stream. 

Steckhan, E., Arns, T., Kromer, L., Hoorman, D., Jorissen, J. and Putter, H., 2000, Some Aspects of Sustainability in Electroorganic Synthesis , Paper presented at 197 meeting of the electochemical society . May 2000, Toronto, Canada, Abstract no. 1036. 

Electroorganic Synthesis by Indirect Electrochemical Methods New Applications of Electrochemical Techniques ... 

Weinberg, N. L. (Ed.), Techniques of Electroorganic Synthesis, Wiley-Interscience, New York, Part 1, 1974, Part 2, 1975. 

M.Aizawa, S.Yabuki and H.Shinohara, Proc. 1st Intemat.Symp. on Electroorganic Synthesis (S.Torii, ed.) Elsevier, Amsterdam, 1987, pp.353-360. 

This review article summarizes the broad area of electroorganic synthesis, (selected electroorganic synthetic reactions, with a special emphasis on those that have been commercialized or investigated in pilot plants) and selected applications of electrochemical techniques for waste-water and effluent treatment. There are a number of modern textbooks and updated reviews [4-53] of electroorganic chemistry that include much more detail on organic reactions and their mechanisms than it is appropriate to discuss here. 

Weinberg NL, Mazur DJ (1990) Industrial electroorganic synthesis in the United States and Canada, Kagaku to Kogyo (Tokyo), 43 2002 (Japan), a review with 23 ref Chem Abstr 114 (1991) 110525e... 

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