Electrosynthesis of Carboxylic Acids

7 Anodic Oxidation of Alcohols and Aliphatic Ethers 3.1.7.1 Electrosynthesis of Carboxylic Acids 

Alcohols can be converted electrochemically into the corresponding carboxylic acids in very good yields if Ni oxide anodes are used in alkaline electrolytes. This reaction was studied intensively in industry for the electrochemical oxidation of diacetone-L-sorbose to diacetone-2-ketogulonic acid (intermediates of the vitamin C synthesis). On the basis of Sowjet work 282 284) (initially Pt anodes and NaBr—NaCl—NiCl2— NaOH electrolytes subsequently Ni oxide anodes), Roche and Merck studied the synthesis on the laboratory and pilot scale. In cooperation with the ETH Zurich 285-286 a special cell 287 288) was developed for this reaction. 

Using this procedure, Roche successfully operated a pilot plant for a capacity of tonnes/day for several thousand hours. By adding very small amounts of Ni salts, it was possible to maintain the anode activity over long periods. The electrochemical process is said to be superior to the conventional hypochlorite process, particularly because of the low level of wastewater pollution 286). However, it appeared not to be sufficiently attractive from an economic point of view to be implemented on an industrial scale in the new Roche plant in Scotland. 

Merck studied the use of iron oxide anodes 289) for this reaction (yields up to 91 %). The rapid loss of electrode activity can be suppressed by adding alkali-resistant solvents, such as anisole or xylene 290). 

To improve the long-term stability of the common nickel oxide anodes, surfactants, such as substituted polyglycol ethers, are added to the electrolyte 291). Merck has proposed a combined process (in which about 80 % of the diacetonesorbose are oxidized electrochemically, and the remainder conventionally 292)) and a special procedure for the work-up procedure by electrodialysis (removal of the unconverted diacetonesorbose 293)). It is said that Merck is using the electrosynthesis of diacetoneketogulonic acid for the industrial production of vitamin C. 

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The addition of carbanions, generated electrochemically by reduction of the carbon-halogen bond, to carbon dioxide has been examined under a variety of experimental conditions. Direct electrosynthesis of carboxylic acids in a divided cell using an aprotic solvent and a tetraalkylammonium salt as electrolyte is most sue-... 

Sock O, Troupel M, Peiichon J (1985) Electrosynthesis of carboxylic acids fn)m organic halides and carlxm dioxide. Tetrahedron LeU 26 1509-1512. doi 10.1016/80040-4039(00)98538-1... 

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]. 

Anodic and cathodic dimerizations often start with esters that are hydrolyzed to the carboxylic acids in a final step the electrosynthesis of sebacic acid [74] and butanetetra-carboxylic [11] acid illustrate this. 

Dimethylhydrazine is currently prepared commercially by a modified Raschig process reacting dimcthylamine with the chloramine produced from ammonia and sodium hypochlorite. Formerly, it was prepared by the reduction of dimethylnitrosamine or by the reductive catalytic alkylation of carboxylic acid hydrazides with formaldehyde and hydrogen, followed by basic hydrolysis (Budavari et al. 1989 EPA 1984a, 1992b lARC 1974 Schmidt 1988). 1,2-Dimethylhydrazine may be prepared from dibenzoylhydrazine or by electrosynthesis from nitromethane (Budavari et al. 1989). 

In organic chemistry well known is the electrosynthesis reaction of Kolbe, in which the electrolysis of sodium salts of carboxylic acids, carried out imder appropriate conditions, leads to the formation of free radicals at the anode. These free radicals undergo decarboxylation and linking with the formation of saturated hydrocarbons ... 

Isochem has set up a multipurpose electrochemical unit devoted to organic electrosynthesis. The unit located in Pithiviers (France) [115] is dimensioned for the production of 80 tons a year of cystein derivatives, such as cysteine base salts, carbocysteine, acetylcysteine, and thiazolidin carboxylic acids. 

R = t-Bu, 81%) and r-butylbenzene (5%) (Scheme 119) [447]. Similarly, the Pd(II) complex catalyzes the electrosynthesis of aromatic carboxylic acids under CO2 atmosphere [448]. The electrocar-boxylation of vinyl triflates is performed with CO2 and a catalytic amount of PdCl2(PPh3)2 to give a,/ -unsaturated carboxylic acids [449]. 

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 electrosynthesis of aromatic carboxylic acids from aryl halides and carbon dioxide is either catalyzed by nickel " or palladium complexes. 

Alraig with the systematic study of the mechanisms of electroorganic reactions and electrochemical and chemical reactivity (aromatic nitro, carbonyl, carboxyl acid, S, Se derivatives, etc.. Dr. Venera Zaripovna Latypova s group), also synthetic works were started. According to Kazan traditions in organophosphorus chemistry, the applicability of electrosynthesis here was first evaluated. Original... 

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