Kolbe electrosynthesis,

Mixed Kolbe electrosynthesis ot two perfluoroacids leads to a mixture of three products, as is generally expected [7S] (equation 69)... 

Electrolysis of carboxylate ions, which results in decarboxylation and combination of the resulting radicals, is called the Kolbe reaction or the Kolbe electrosynthesis. 

Cathodic hydrogen evolution is also of some significance as a counterelectrode reaction in anodic organoelectrosyntheses as, for instance, in the Kolbe electrosynthesis of sebacic acid (63) or the anodic oxidation of toluenes to benzaldehydes (64). 

Several theories have been proposed to account for the Kolbe electrosynthesis one, which has been widely held, is that the acetate ions are discharged directly at the anode and the resulting radicals then react in pairs, thus... 

In non-aqueous solutions the Kolbe electrosynthesis takes place with high eflSciency at platinized platinum and gold, as well as at smooth platinum, anodes increase of temperature and the presence of catalysts for hydrogen peroxide decomposition, both of which have a harmful effect in aqueous solution, have relatively little influence. The mechanism of the reaction is apparently quite different in non-aqueous solutions and aqueous solutions in the former no hydroxyl ions are present, and so neither hydroxyl radicals nor hydrogen peroxide can be formed. It is probable, therefore, that direct discharge of acetate ions occurs at a potential which is almost independent of the nature of the electrode material in a given solvent. The resulting radicals probably combine in pairs, as in aqueous solution, to form acetyl peroxide, which subsequently decomposes as already described. ... 

Electrolytic decarboxylative coupling of sodium salts of carboxylic acids takes place during their electrolysis. Carbon dioxide is eliminated, and the free radicals thus generated couple to form hydrocarbons or their derivatives. The reaction is referred to as the Kolbe electrosynthesis and is exemplified by the synthesis of 1,8-difluorooctane from 5-fluorovaleric acid (equation 469) [574]. Yields of homologous halogenated acids range from 31% to 82% [574]. 

In Kolbe electrosynthesis the carboxylate ion loses an electron and then carbon dioxide [Eq. (18)] this reaction is discussed in Chapter 14. A number of electrochemical reactions involve a cleavage of the bond between the central metal atom and one or more ligands. Such reactions are not discussed here. 

A typical example is the Kolbe electrosynthesis in which a carboxylate salt is electrochemically discharged at vitreous carbon anodes, in both aqueous and nonaqueous media, yielding a hydrocarbon with high efficiency and carbon dioxide. 

Willstatter s second synthesis (36) involved the condensation of methylamine with succinyldiacetic ester (Kolbe electrosynthesis on the monopotassium salt of the monoethyl ester of acetonedicarboxylic acid (35)), reduction (Hj - - Pt) of the resulting diethyl A-methylpyrrolediacetate and cyclization (Na + p-cymene) of the cis form of diethyl A-methylpyrroli-dinediacetate to ethyl tropinone-2-carboxylate. Hydrolysis of the ester to tropinone and its reduction (Zn - - HI) to tropine (147) completed the... 

The success of the Kolbe electrosynthesis and the method of reduction of monosaccharides with sodium amalgam that was introduced by... 

Kolbe Synthesis, Kolbe Electrosynthesis, Kolbe Electrolytic... 

This reaction has also been studied extensively and has broad synthetic applications. A simple route to the synthesis of many dicarboxylic acids is an extension of the Kolbe electrosynthesis, being the electrolysis of the half esters of dicarboxylic acids ... 

It can be seen that the Involvement of free radicals in the Kolbe electrosynthesis is actually not the question. Rather, it is whether these radicals are free to react homogeneously in solution —although formed by a concerted electron transfer/decarboxylation process at the electrode surface—or are adsorbed In an excellent review of the anodic reactions of carboxylates, Utley " has presented a reaction scheme (shown in part below) which is adequate for most purposes. In a concluding section of this review, the question of free radical intermediates vis a vis adsorbed radicals is discussed in considerable detail. However, it would seem that the only conclusion one can draw is that the mechanism of this electro-organic process is still by no means settled. However, the following steps are likely to be involved ... 

The principal theories of the mechanism of the Kolbe electrosynthesis, as discussed earlier, have been criticized. A satisfactory summary of these has been presented by Dickinson and Wynne-Jones. The main points of disagreement among these theories are, (a) whether the hydroxyl ion or the carboxylate ion is discharged at the anode, (b) the explanation of the effect of the electrode material on the reaction, and (c) the reason for the occurrence of the Kolbe synthesis in preference to oxygen evolution which could occur at lower anode potentials. Recent experimental investigations, particularly those of Dickinson and Wynne-Jones and of Conway and Dzieciuch permit a detailed analysis of the mechanism of the Kolbe reaction, in both aqueous and nonaqueous media. 

Eberson L (1967) Mechanism of the kolbe electrosynthesis. Electrochim Acta 12 1473-1478... 

Hickting,A., Wilkins,R. Effect of current pulsing on current efficiencies of the Brown-Walker and Kolbe electrosynthesis. Discussions Faraday Soc. 45, 261 (1968). 

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