Oxidation of carboxylic acids

Oxidation of Carboxylic Acids and Their Functional Derivatives... 

The study of optical isomers has shown a similar development. First it was shown that the reduction potentials of several meso and racemic isomers were different (Elving et al., 1965 Feokstistov, 1968 Zavada et al., 1963) and later, studies have been made of the ratio of dljmeso compound isolated from electrolyses which form products capable of showing optical activity. Thus the conformation of the products from the pinacolization of ketones, the reduction of double bonds, the reduction of onium ions and the oxidation of carboxylic acids have been reported by several workers (reviewed by Feokstistov, 1968). Unfortunately, in many of these studies the electrolysis conditions were not controlled and it is therefore too early to draw definite conclusions about the stereochemistry of electrode processes and the possibilities for asymmetric syntheses. 

Anodic Oxidation of Carboxylic Acids Without Decarboxylation... 

The oxidation of carboxylic acids with H2O2 and an acid catalyst is the best general... 

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... 

As an example we may consider the Kolbe reaction, the oxidation of carboxylic acid and carboxylates of the form R-COOH or R-COO- to form coupled hydrocarbon products of the form R2. Investigation of this reaction in aqueous and non-aqueous solvents has revealed that the processes taking place are very complex indeed. In general, the product R2 is only formed at high current densities on smooth electrodes. At lower current densities, alkenes and non-dimeric products such as R-H are found, and, especially in alkaline solutions, the product R-OH can be formed in good... 

Cations resulting from a two-electron oxidation of carboxylic acids (non-Kolbe electrolysis) or from compounds having protons in the a-position to heteroatoms as shown in Scheme 3 [6] react with nucleophilic centers. In the last case. 

Substituents stabilising a carbonium ion influence the course of the anodic oxidation of carboxylic acids by promoting fast oxidation of the radical intermediate to the carbonium ion. Subsequent chemical steps are those expected of this ionic intermediate and the overall process is termed the non-Kolbe reaction. Reaction at... 

Polymer supported persulfonic acids can be prepared by treating polymer-bound sulfonic acids with H2O2 or K2S20g. The resulting resin was found to display an activity of 2.5 mole equivalents per gram of wet resin. This persulfonated resin was successively applied for the oxidation of carboxylic acids, ketones, olefins and for the cleavage of disulfide linkage and of A-formylamino acids. 

Oxidation of Carboxylic Acids to Peroxy Acids Peroxy-de-hydroxy-substitiition... 

The oxidation of carboxylic acids with H202 and an acid catalyst is the best general method for the preparation of peroxy acids.450 The most common catalyst for aliphatic R is concentrated sulfuric acid. The reaction is an equilibrium and is driven to the right by removal of water or by the use of excess reagents. For aromatic R the best catalyst is methanesulfonic acid, which is also used as the solvent. 

Diacyl peroxides (16, R2 = R1 = alkyl or aryl) have been obtained from the oxidation of carboxylic acid potassium salts by Kolbe electrolysis or by elemental fluorine. 

A combination of majority and minority carrier processes has been observed to produce quantum yields in excess of one at both n- and p-type interfaces. In all cases where this has been noted, the redox species employed have been capable of multiple-electron processes. This type of behavior is often seen for the oxidation of carboxylic acids at n-type semiconductors (a two-electron process). It has also been noted for hydrazine oxidation (a four-electron process) and the reduction of hydrogen peroxide. 

Of particular interest in this context has been the finding that the Kolbe reaction, the anodic oxidation of carboxylic acids (Equation 1) (2), can be made to occur at n-type oxide semiconductor photoanodes to the virtual exclusion of oxygen formation (3,4,5). 

If this is true, then the oxidation of carboxylic acids should be the preferred process on SrTi03 photoanodes, in the absence of such defect surface states. We see from Figure 5 that the range of potentials reported for the normal Kolbe reaction (at platinum) actually crosses the valence band levels of both SrTiC>3 and Ti02 in the neutral pH region. It may well be that at high pH, the photo-Kolbe potential lies at or below the valence band edge for these semiconductors, consistent with the observation that photo-Kolbe products are not observed under these conditions. 

Anodic oxidation of carboxylic acids bearing a trimethylsilyl group on the -position gives exclusively terminal olefins in rather good yields. The reaction seems to proceed via a carbocation intermediate formed by the oxidative elimination of CO2 (equation 42)46. 

This review describes the electrochemical behavior of compounds containing the C=C, C=0 and C=N functional group. The review covers both anodic oxidation and cathodic reduction of such compounds. The electrochemistry of these functionalities was reviewed in an earlier volume of this series1 this article updates the previous one but does not include the material included there. The Kolbe oxidation of carboxylic acids has... 

Kolbe-type alkylations are, of course, oxidative in nature. There are a few other oxidative processes which lead to perfluoroalkylative addition, namely oxidation of carboxylic acids with xenon difluoride and oxidation of sodium per-fluoroalkylsulfinates [63,287]. 

Reactions have been described for RH = amines, alcohols, aromatics, aliphatics, perfluoroalkyls, hydrogen halides, and thiols (167). Another recent use of S2OfiF2 in organic chemistry has been in the synthesis of lactones by the remote oxidation of carboxylic acids using a... 

For applied purposes, the book by Mitskevich and Erofeev [31] is of interest because it discusses conjugated reactions on the example of decarboxylation processes accompanying the liquid-phase oxidation of carboxylic acids. 

Gandini D, Mahe E, Michaud PA, Haenni W, Perret A, Comninellis C. Oxidation of carboxylic acids at boron-doped diamond electrodes for wastewater treatment. J Appl Electrochem 2000 30 1345-1350. 

An alternative route for the oxidation of carboxylic acids not involving decarboxylation has been demonstrated for the reaction of manganese-(III)219 221 232 234 and cerium(IV).238a-b Carboxymethyl radicals are formed in the reaction. 

Huang L, Colas C, Ortiz de Montellano PR (2004) Oxidation of carboxylic acids by horseradish peroxidase results in prosthetic heme modification and inactivation. J Am Chem Soc 126 12865-12873... 

Kolbe synthesis — The definition and use of the terms - Kolbe synthesis, K. reaction, K. electrolysis, and K. process are not very clearly distinguished and often bear different nuances of meaning. Kolbe electrolysis or synthesis mainly accounts for the anodic oxidation of carboxylic acids or carboxylates, followed by a decarboxylation step, when concentrated aqueous solutions of the respective carboxylates are electrolyzed. Kolbe picked up earlier results from -> Faraday on the electrolysis of acetic acid or acetate solutions to CO2 and ethane [i] and continued these experiments during 1843-1845 with further homologs as, e.g., valerianic acid [ii]. The carboxy-late R-COO- is anodically oxidized to form an unstable radical R-COO, which is stabilizing via a decarboxylation reaction, leaving radical rest R ... 

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