Reduction of Organic Compounds

T. L. Ho, Reduction of organic compounds with low-valent species of Group IV B, V B and VIB metals. Synthesis 1979, 1. 

H.G. Kuivii.a, Reduction of Organic Compounds by Organotin Hydrides, Synthesis 1970, 499. 

J.M. Lalancette et al., Reduction of Functional Groups with Sulfurated Borohydrides, Synthesis 1972, 526. J. Malek u. M. Cerny, Reduction of Organic Compounds by Alkoxyaluminohydrides, Synthesis 1972, 217. S.-C. Chen, Molecular Rearrangements in Lithium Aluminium Hydride Reduction, Synthesis 1974, 691. 

C. F. Lane, Reductions of Organic Compounds with Dihorane, Chem. Reviews 76, 773 (1976). 

F. D. Popp u. H.P. Schultz, Fdectrolytic Reduction of organic Compounds, Chem. Reviews 62, 19 (1962). 

Many of these cobalt complexes will catalyze the reduction of organic compounds by borohydride, hydrazine, thiols, etc. Cobalt cyanide complexes will catalyze the reduction of a,j8-unsaturated acids by borohydride (105) DMG complexes the reduction of butadiene and isoprene by borohydride, but not by H2 (124) Co(II) salen, the reduction of CHCI3 and CH3CCI3 to the dichloro compounds by borohydride (116) and cyanocobalamin, the selective reduction of -CCI2- by borohydride to -CHCl- in compounds such as aldrin, isodrin, dieldrin, and endrin without... 

In the present chapter we want to look at certain electrochemical redox reactions occurring at inert electrodes not involved in the reactions stoichiometrically. The reactions to be considered are the change of charge of ions in an electrolyte solution, the evolution and ionization of hydrogen, oxygen, and chlorine, the oxidation and reduction of organic compounds, and the like. The rates of these reactions, often also their direction, depend on the catalytic properties of the electrode employed (discussed in greater detail in Chapter 28). It is for this reason that these reactions are sometimes called electrocatalytic. For each of the examples, we point out its practical value at present and in the future and provide certain kinetic and mechanistic details. Some catalytic features are also discussed. 

Electrochemical reduction of organic compounds in aprotic solvents is a very suitable way for preparing reactive anionic intermediates of great synthetic value [148]. Carbanions electrogenerated from organic halides readily react with various electrophiles. 

Several efforts were made in order to circumvent these difficulties. In the preparatively interesting reduction of organic compounds such as dienes. 

Dissolving metal reductions were among the first reductions of organic compounds discovered some 130 years ago. Although overshadowed by more universal catalytic hydrogenation and metal hydride reductions, metals are still used for reductions of polar compounds and selective reductions of specific types of bonds and functions. Almost the same results are obtained by electrolytic reduction. 

Iron was one of the first metals employed for the reduction of organic compounds over 130 years ago. It is used in the form of filings. Best results are obtained with 80 mesh grain [765]. Although some reductions are carried out in dilute or concentrated acetic acid the majority are performed in water in the presence of small amounts of hydrochloric acid, acetic acid or salts such as ferric chloride, sodium chloride (as little as 1.5-3%) [765], ferrous sulfate [766] and others. Under these conditions iron is converted to iron oxide, Fe304. Methanol or ethanol are used to increase the solubility of the organic material in the aqueous medium [766] (Procedure 34, p. 213). 

Divalent chromium salts show very strong reducing properties. They are prepared by reduction of chromium(III) compounds with zinc [187] or a zinc-copper couple and form dark blue solutions extremely sensitive to air. Most frequently used salts are chromous chloride [7SS], chromous sulfate [189], and less often chromous acetate. Reductions of organic compounds are carried out in homogeneous solutions in aqueous methanol [190], acetone [191], acetic acid [192], dimethylformamide [193] or tetrahydrofuran [194] (Procedure 37, p. 214). 

Similar reductions are achieved by trialkylboranes [S26]. These reactions, although different in nature from the reductions by hydrides and complex hydrides, were amongst the first applications of boranes and alanes for the reduction of organic compounds. 

The astronomical number of reductions of organic compounds described in the literature makes an exhaustive survey impossible The most complete treatment is published in Volumes 4/lc and 4/ld of the Houben-Weyl compendium Methoden der Organischen Chemie. Other monographs dealing mainly with sections of this topic are listed in the bibliography (p.257). 

Chapter 1 - Electrochemical Oxidation and Reduction of Organic Compounds,... 

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