Carbon electrochemical carboxylation

Recent Scientific and Technological Developments in Electrochemical Carboxylation Based on Carbon Dioxide... 

Dunach, Inesi and others also investigated the electrochemical synthesis of cyclic carbonates from C02 with epoxides, alcohols and glycols [66]. In this regard, Yang et al. [67] reported the use of pure room temperature ionic liquids (ILs) as reaction media in the electrochemical activation of C02 for the synthesis of cyclic carbonate from epoxide, under mild conditions. C02-saturated IL (BMIMBF4) solutions were also used for the electrochemical carboxylation of activated olefins [68]. Monocarboxylic acids were obtained in moderate yield (35-55%), and the IL was recycled five times. 

Electrochemical carboxylation of aryl and enol triflates occurs in DMF using carbon dioxide and (Ph,P)2PdCL in DMF. 

Sanchez-Sanchez, C.M., Expdsito, E., Batanero, B., Montiel, V, Barba, F., and Aldaz, A. 2004. Electrochemical carboxylation. Carbon dioxide could be useful compound for synthesis. In Trends in Electrochemistry and Corrosion at the Beginning ofthe 21st Century. Brillas, E., and Cabot, P.-L., Eds. Universitat de Barcelona, Barcelona, pp. 431-442. 

A v ety of reactions are catalyzed by electrochemically generated Ni(0) (62). Electrochemical reduction of Ni(bipy)3Br2 affords a reagent that couples acid chlorides and alkyl or aryl halides to form unsymmetrical ketones (63). Symmetrical ketones are formed from alkyl halides and carbon dioxide (64). Reductive electrochemical carboxylation of terminal alkynes, enynes and diynes can be accomplished with 10% Ni(bipy)3(Bp4)2 in DMF (65-68). Terminal allies lead selectively to a-substituted acrylic acids. Electrocatalytic hydrogenation on hydrogen-active electrodes has been reviewed (69). Radical cyclizations of vinyl, alkyl and aryl radicals can be carried out by indirect electrochemical reduction with a Ni(II) complex as a mediator (70). 

Hiejima Y, Hayashi M, Uda A, Oya S, Kondo H, Senboku H, Takahashi K (2010) Electrochemical carboxylation of a-chloroethylbenzene in ionic liquids compressed with carbon dioxide. Phys Chem Chem Phys 12(8) 1953-1957. doi 10.1039/b920413j... 

Electrochemical Fixation of Carbon Dioxide (Cathodic Reduction in the Presence of Carbon Dioxide), Scheme 3 Electrochemical Carboxylation subsequent to Cyclization... 

Platinum, grassy carbon, graphite, stainless steel, carbon fiber, silver, lead, mercury pool, and some other metals are reported to be usable as cathode materials in electrochemical carboxylation. Among them, platinum, stainless steel, carbon fiber, and graphite are frequently used for an efficient formation of carboxylic acid by electrochemical fixation of carbon dioxide with a sacrificial anode, such as magnesium and aluminum [1-4], as a couple in an undivided cell (one-compartment cell). 

One of great synthetic applications of electrochemical fixation of carbon dioxide is synthesis of 2-arylpropanoic acids, nonsteroidal anti-inflammatory drugs (NSAlDs), and their derivatives. Electrochemical carboxylations of benzyl halides [1, 3, 8-13], aryl methyl ketones [14, 15], and a-bromostyrenes [16] are reported to be successfully applied to the synthesis of several NSAIDs, such as ibuprofen and naproxen, and their precursors and derivatives (Scheme 4). 

Zhang K, Wang H, Zhao S, Niu D, Lu J (2009) Asymmetric electrochemical carboxylation of prochiral acetophenone an efficient route to optically active atrolactic acid via selective fixation of carbon dioxide. J Elctroanal Chem 630 35-41... 

Sasaki A, Kudoh H, Senboku H, Tokuda M (1998) Electrochemical carboxylation of several organic halides in supCTcritical carbon dioxide. In Torii S (ed)... 

Tokuda et al. also reported that electrochemical carboxylation of benzyl chloride, cinnamyl chloride, and 2-chloronaphthalene was smoothly proceeded in supercritical carbon dioxide-DMF media (Scheme 2) [8]. A mixture used in this work also exhibited the ability to solvate polar electrolytes like ammonium salts. In these reactions, since carbon dioxide plays the role of a reactant, C02-rich conditions such as supercritical conditions are quite suitable for improving the product yields. 

Electrochemical carboxylation of a-halogenated arenes under the carbon dioxide atmosphere with zinc anode afforded the effective formation of phenylpropionic acid derivatives in high yield. This method is application of carboxylation of aromatic halides with reactive metal anode to synthesis of a f -inflammatory pharmaceutical drugs. 

Derien S, Clinet J-C, Dunach E, Perichon J (1993) Activation of carbon dioxide nickel-catalysed electrochemical carboxylation of diynes. J Org Chem 58 2578-2588... 

Recently, acylsilanes have been utilized as useful intermediates in organic synthesis [57], For example, treatment of acylsilanes with the fluoride ion generates the corresponding acyl anions which react with electrophiles. On the other hand, by using the electrochemical method, acylsilanes serve as acyl cation equivalents because nucleophiles are introduced at the carbonyl carbon. Chemical oxidation of acylsilanes with hydrogen peroxide which affords the corresponding carboxylic acids has been reported [58], However, the anodic oxidation provides a versatile method for the introduction of various nucleophiles... 

The direct electrochemical reduction of carbon dioxide requires very negative potentials, more negative than —2V vs. SCE. Redox catalysis, which implies the intermediacy of C02 (E° = —2.2 V vs. SCE), is accordingly rather inefficient.3 With aromatic anion radicals, catalysis is hampered in most cases by a two-electron carboxylation of the aromatic ring. Spectacular chemical catalysis is obtained with electrochemically generated iron(0) porphyrins, but the help of a synergistic effect of Bronsted and Lewis acids is required.4... 

Perhaps the best-known and most widely appreciated electrochemical transformation is the Kolbe oxidation (see also Chapter 6) [1, 2, 31]. The process involves the one electron oxidation of the salt of a carboxylic acid, and the loss of carbon dioxide to afford a radical, R, that subsequently engages in coupling reactions. Both symmetrical (R + R ) and nonsym-metrical (R + R ) radical couplings are known and are illustrated in the following discussion. The nonsymmetrical variety (often referred to as a mixed or hetero coupling) is remarkable given that it requires the cogeneration and reaction of more than one reactive intermediate. 

An electrochemical explanation of the basic reaction was suggested by P rumkin 17), while Shilov et al. 22, 23) claimed surface oxides of definite structure to be the only cause of either acidic or basic reaction. Shilov formulated the acidic surface oxides as carboxylic acid anhydrides bound to the edges of the carbon layers. 

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-... 

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