Acetophenones electroreduction

Related to these enzyme -catalysed reactions are electroreductions of acetophenone in the presence of chiral crown ethers. The low optical yields (<3%) are attributed to association of the prochiral substrate and the chiral crown ether salt complex in the electrochemical double layer (Horner and Brich, 1978). 

Antimony(III) trichloride can be used as a catalytic mediator in the electroreduction of carbonyl compounds. The advantage of the procedure is illustrated by the selective reduction of acetophenones (497), leading to the corresponding benzylic alcohols (498) (Scheme 173) [575]. The electroreduction is performed in an EtOH/BuOH(l/1.5)-aq.HCl-(Pt/Pb) system in the presence... 

Fletcher and Razaq studied the four-electron reduction of acetophenone to ethylbenzene in strongly acidic media. Such an electroreduction is analogous to the classical Clemmensen reaction, which is carried out with amalgamated zinc in concentrated hydrochloric acid. 

Ethylation of l,2-dithiole-3-thione gives a 3-ethylthio-l,2-dithiolylium ion whose electroreductive dimerization has been investigated. A series of aryl-substituted l,2-dithiol-3-ylidene acetophenones underwent oxidative dimerization via cation-radicals (142) when electrolyzed the dimeric products, which contain a new C—C bond, were elaborated chemically into a series of highly conjugated derivatives including bithiathiophthenes. " ... 

Very significantly, recent studies by Pleus and coworkers108 have revealed that the conducting films 5 and 6 may be employed as chiral electrodes for the enantioselec-tive electroreduction of acetophenone and 4-methylbenzophenone in DMF to their corresponding alcohols, using DMF/LiBr as electrolyte and phenol as the proton donor. The nature of the electrolyte used for electrodeposition of the polymers influenced the optical purity of the chiral alcohol products obtained with enantioselec-tivities as high as 58% being achieved. 

Ionic liquids are also effective for electrochemical reductive coupling reactions. For example, the cathodic reduction of benzaldehyde in [bmpyr][NTf2] [bmpyr = 1-butyl-1-methylpyrrolidinium NTf2 = bis(trifluoromethylsulfonyl) imide] gave rise to dimerization [9]. Electroreductive coupling of acetophenone in ionic liquids gave the corresponding pinacol as a mixture of diastereomers (Equation 12.3) [10]. 

Overall electrochemical reduction processes may be represented in terms of several electron transfers, proton transfers, and chemical reactions, as is shown below by the electroreduction of acetophenone [(X), Scheme 4]. 

The electroreduction of acetophenone in acidic electrolytes has been the subject of detailed studies of both the electrode kinetics and the reaction products. One important question that has arisen from this work... 

The dimerization reaction, illustrated by the formation of the pinacol in the electroreduction of acetophenone, is an obvious example of a coupling reaction. Such reactions may occur between radicals or radical ions generated in either an anodic or a cathodic process. For example, an electrochemical process in which radicals are generated anodically is the classical Kolbe reaction, the electrolysis of carboxylates ... 

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