History of Organic Electrosynthesis - American Chemical Society


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Chapter 13

History of Organic Electrosynthesis Manuel M . Baizer1 Department of Chemistry, University of California, Santa Barbara, C A 93106 Downloaded by UNIV OF LEEDS on July 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1989 | doi: 10.1021/bk-1989-0390.ch013

Very many types of organic synthesis can now be carried out electrochemically, often more advantageously than by other means. Organic electrosynthesis, always multi-disciplinary, now includes photoelectrochemistry, electro-catalysis, bioelectrochemistry and others. Some of the scientific and technological developments which led to the present status of the field will be cited: the use of potential control, the invention of the potentiostat, the combination of electrochemistry with spectroscopy, the use of ion-selective membranes; the large-scale production of sorbitol, adiponitrile, and dimethyl sebacate. 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. The first experiment in organic electrochemistry was said to have been the transformation of wine into vinegar. This was of course not a synthesis but a practice, electrochemical or not, that still seems to be followed by the French wine industry in exporting moderately priced products to the U.S. Nor was Faraday's observation of the formation of a gaseous hydrocarbon from acetic acid a synthesis. He was too preoccupied with other activities to pursue this finding and develop the Kolbe Reaction. Hermann Kolbe, however, did go much further and developed a reaction which is one of the widely used in organic electrosynthesis, namely the oxidation at platinum of carboxylates to hydrocarbons (oxidative decarboxylation):

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In Electrochemistry, Past and Present; Stock, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Several variants have become established. The Hofer-Moest Reaction uses carbon rather than platinum anodes; the intermediate radical loses another electron and becomes a carbocation which reacts with nucleophiles (Nu)- purposely added or adventitiously present (e.g., OH" from water):

Downloaded by UNIV OF LEEDS on July 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1989 | doi: 10.1021/bk-1989-0390.ch013

A second variant is the Crum Brown-Walker oxidation of monocarboxylate monoesters to diesters:

This process is commercial for the preparation of sebacates from adipates because, in spite of the loss of a substantial portion of the molecular weight as CO2, it is more economical than the alternatives. Fritz Haber showed that for selective syntheses it is more important to control the electrode voltage than to select a given electrode material. E.g., nitrobenzene can, depending on pH, be reduced to a variety of products including those of condensation and rearrangement but, with certain limitation, can be reduced largely to one specific product by controlling the cathode potential. This type of control was not automated until the 1940's when Hickling (Liverpool) designed and demonstrated the first potentiostat. This development provided one of the most important tools of organic electrosynthesis. Of inestimable value also has been the invention of polarography by Nobel Laureate J. Heyrovsky (first at Charles University in Prague then at the Institute which now bears his name). It became possible to detect, sometimes quantitatively, a mixture of metallic ions or several functional groups in one molecule using the dropping mercury electrode and regularly increasing the cathode voltage in the negative direction. One of his students, Petr Zuman (now at Clarkson University) used the polarography of organic compounds to clarify the reactions occurring in the course of the reduction. Kolthoff introduced the techniques in the U.S. and extended it; he and Lingane are the authors of a two-volume book on the subject. S. Wawzonek (University of Iowa) concentrated on the polarography of organic compounds. He used as solvents organic compounds (e.g., dioxane, alcohol) diluted with a little water therefore these were not aprotic systems - and usually helped elucidate the polographic phenomena by means of preparative-scale experiments. At one time polarography was the most widely used analytical technique in the world. Variants, particularly of wave-form, have been invented. However the technique has been supplemented and in many cases replaced by cyclic voltammetry which gives reduction (and oxidation potential) and, at the same time, information on the rapidity (reversibility) of the electron-transfers, i.e., on the kinetics of the reactions. In this area seminal work was done by Nichols and Shain both then at the University of Wisconsin. In addition to doing much original research on organic electrosynthesis Fr. Fichter (Basel) produced the first

In Electrochemistry, Past and Present; Stock, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Downloaded by UNIV OF LEEDS on July 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1989 | doi: 10.1021/bk-1989-0390.ch013

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ELECTROCHEMISTRY, PAST AND PRESENT

authoritative book on the entire subject ("Organische Elektrochemie", Steinkopff, Dresden and Leipzig, 1942). This has served as a complete guide to the literature until the time it was published. Since 1973 there have been several comprehensive but not encyclopedic books on the subject. A bibliography of Electroorganic Syntheses 1801-1975 was published in 1980 (The Electrochemical Society Inc.). It had been a life-long project of Sherlock Swann, Jr. (University of Illinois) and was brought to completion by Richard Alkire (University of Illinois). Four volumes (XI-XIV, 1978-80) of the Encyclopedia of Electrochemistry of the Elements (Marcel Dekker, Inc.) under the general editorship of A. J. Bard were edited by H. Lund and are the Organic Section. With some exceptions there was a hiatus of activity in this area from about 1940 to 1955. In the U.S. Swann, mentioned above, kept the field alive and in Japan Kiichiro Sugino. (They were acquainted with each other.) Swann, from a background in metallurgy, emphasized electrode (usually cathode) material, shape, method of preparation, etc. Sugino, an organic chemist, was interested in the synthetic results, less so with mechanisms of reactions except speculatively. However, there was one outstanding development: the commercialization of the electrochemical process for reducing glucose to sorbitol (+ mannitol) which grew out of the work of H. J. Creighton. This was practiced by the Atlas Powder Co. 1937-1948 and replaced by a catalytic process. A new dimension was added to at least the understanding of organic electrosyntheses by combining electrolysis with spectroscopy to yield information on the nature of the first-formed intermediate and the kinetics of the follow-up reaction(s). One early development was the characterization of nitro-aromatic anion radicals by electron-spin-resonance (e. s. r.) spectroscopy due to D. H. Geske and his associates. This field has expanded enormously and now includes internal reflectance, resonance Raman, specular reflectance and transmission spectroscopies. This range of techniques is now commonly used in elucidating mechanisms: A. Bewick and M. Fleischmann (University of Southampton, England), A. J. Bard (Austin, Texas), D. H. Evans (University of Delaware), Vernon Parker (Trondheim), J.-M. Saveant (University of Paris). The field of electrochemical polymerization, after a shaky start, began to develop on a rational basis about 1960 due to the efforts of J. W. Breitenbach (University of Vienna) and B. L. Funt (now at Simon Fraser University in Vancouver). To the best of my knowledge none of these processes has been commercialized; further research is being overshadowed by the frantic activity in the field of conducting polymers (A. MacDiarmid, University of Pennsylvania, A. Heeger and F. Wudl, University of California at Santa Barbara, A. Diaz, I.B.M., San Jose, CA) . The entire field of organic electrosynthesis received its biggest stimulus in about 1965 after Nalco's tetralkylleads and Monsanto's adiponitrile process were commercialized. In the former case, non-aqueous media were used successfully on a large scale; in the latter a relatively inexpensive product was made on a multi-tonnage basis thus finally upsetting the old dictum that electrochemical methodology could be considered for the production only of speciality chemicals, medicinals, etc. This upsurge was

In Electrochemistry, Past and Present; Stock, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Downloaded by UNIV OF LEEDS on July 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1989 | doi: 10.1021/bk-1989-0390.ch013

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nowhere more noticeable than in Japan which now has probably the most extensive programs in the world. Outstanding results have been achieved by Y. Ban (Hokkaido), T. Osa (Tohoku University in Sendai), T. Shono (Kyoto), S. Torii (Okayama), T. Nonaka (Graduate School, Tokyo Institute of Technology), I. Nishiguchi (Municipal Technical Institute, Osaka) and their co-workers. Although its history encompasses only the last fifteen years insofar as its relevance to organic electrosynthesis is concerned, the study and development of chemically modified electrodes (C.M.E.'s) has stimulated a great deal of work which may eventually lead to unique syntheses. L. L. Miller (now at the University of Minnesota) attached covalently to oxidized surfaces of graphite a chiral moiety which, it was hoped, would induce chirality during a cathodic reduction. The results were very modest but encouraging. What does this brief review of the highlights of the history of organic electrosynthesis tell us about the state of its health? It is alive and well and living in all industrial countries in the world. If has progressed on the basis of a wealth of ideas that this methodology has inspired. It has been accompanied (necessarily) by the development of instrumentation to test, modify, and refine these ideas. It has spawned new sub-areas whose impact upon the field cannot yet be assessed. A review paper written in 2001 covering the period from 1950 will undoubtedly recount more exciting developments than were produced in the century and a half 1801-1950. RECEIVED August 3, 1988

In Electrochemistry, Past and Present; Stock, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.