Carboxylic acids electrolytic decarboxylation

The electrolytic decarboxylations of either cis- or trari5-bicyclo[3.1.0]hexane-3-carboxylic acids (74), gave the same products although in different ratios. The... 

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]. 

Experimental variables affecting the course of the electrolytic decarboxylation of carboxylic acids are summarized in Table 2. For the Kolbe dimerization, the conditions specified for a one-electron process are recommended otherwise the reaction through carbenium ion (non-Kolbe reaction) may occur predominantly. It should be emphasized that even under the conditions most favorable for the Kolbe dimerization, the cation-derived products are usually formed to some extent or, in particular cases, as a major product, depending on the structure of the employed carboxylic acid. 

Electrolysis of A-carbamoylaspartic acid or A-ethoxycarbamoylaspargine in MeOH-MeONa-(C) affords the corresponding methoxylated products [140], A 5-fluorouracil derivative (LXIII), a potent antitumor agent, can be prepared via electrolytic methoxylation of A-acylazacycloalkane-2-carboxylic acids (LXI) in MeOH-MeONa-(C) and subsequent condensation of (LXII) with 2,4-bis-(trimethylsilyl)-5-fluorouracil (TMS-5-FU) [Eq. (31)] [133,141]. Recently, the decarboxylative methoxylation of o -amino acids has been extended to prepare useful chiral building blocks [127-130]. 

By anodic decarboxylation carboxylic acids can be converted simply and in large variety into radicals. The combination of these radicals to form symmetrical dimers or unsymmetrical coupling products is termed Kolbe electrolysis (Scheme 1, path a). The radicals can also be added to double bonds to afford additive monomers or dimers, and in an intramolecular version can lead to five-membered heterocycles and carbocycles (Scheme 1, path b). The intermediate radical can be further oxidized to a carbenium ion (Scheme 1, path c). This oxidation is favored by electron-donating substituents at the a-carbon of the carboxylic acid, a basic electrolyte, graphite as anode material and salt additives, e.g. sodium perchlorate. The carbocations lead to products that are formed by solvolysis, elimination, fragmentation or rearrangement. This pathway of anodic decarboxylation is frequently called nonKolbe electrolysis. 

The radicals generated by anodic decarboxylation of carboxylic acids can be intercepted by alkenes that are present in the electrolyte. The adduct radical can couple with the radical generated from the car-boxylate to form an additive monomer I (Scheme 8 path a), it can dimerize to form an additive dimer II (path b), it can be further oxidized to a cation, which reacts with a nucleophile to form III (path c), or it can disproportionate (path d). 

Kolbe electrolytic synthesis. Formation of hydrocarbons by the electrolysis of alkali salts of carboxylic acids (decarboxylative dimerization). 

A polymer electrolyte membrane (PEM) reactor is described by Hicks and Fedkiw [2.454] for use during Kolbe electrolysis, which involves the anodic oxidation of an alkyl carboxylic acid, and its subsequent decarboxylation and coupling to produce a dimer. 

Unsaturated carboxylic adds (23) can be electrolytically decarboxylated to allylic acetates (24) in 80—90% yield. a-Phenylthiocarboxylic acids can also be decarboxylated electrolytically to give high yields of aldehyde acetals (c/. 3, 49). Electrolytic procedures are also useful for the conversion of malonic acids into ketones. " This method has been used to prepare valerolactones from cyclic ethers (25), themselves prepared by Diels-Alder reactions between dienes and ketomalonates. ... 

The decarboxylation of acids may take place by both radical and ionic processes. Radical processes involving the electrolytic discharge of a carboxylate anion (the Kolbe reaction ) may give rise to dimeric products. 

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