Crum Brown-Walker reaction

Crum Brown-Walker reaction, 4 Cuprous chloride, 42, 121 1-Cyanocyclopropanecarboxylic acid, 69... 

Chromium trioxide, 60, 21 Clemmensen reaction, 60, 111 Copper chloride (CuCl) [7758-89-6], 61, 122 Crotonic acid, ethyl ester, ( )-, 61, 85 18-Crown-6-potassium cyanide complex, 60,129 Crum Brown-Walker reaction, 60, 4 Cuprous chloride, 60, 42, 121 61, 122 CYANIC ACID, PHENYL ESTER [1122-85-6], 61, 35... 

Kolbe Electrolytic Synthesis Crum Brown-Walker Reaction... 

The dimerization of half-esters is known as the Crum Brown-Walker reaction A. Crum Brown, J. Walker, ibid. 261,107 (1891). 

In aqueous and related media, most of the chemistry of organic electrode reactions is concerned with species resulting from the eventual uptake of one electron and one proton or, more usually, two electrons and two protons (in cathodic reactions) and the reverse processes in some anodic reactions. However, in the latter reactions, the formation of radical intermediates as a result of de-electronation may lead to other chemical changes, e.g., in the total oxidation of hydrocarbons to carbon dioxide in aqueous media and in other ways in the Kolbe, Hofer-Moest and Crum Brown-Walker reactions, and some other carbonium ion type rearrangements. 

The Brown-Walker Electrosynthesis.—The salts of normal dicar-boxy lie acids do not undergo an oxidation similar to the Kolbe reaction, but alkali metal salts of the semi-esters, viz., C02Et(CH2)nC02K, do, however, give a reaction of the same type this process was discovered by Crum Brown and Walker (1891) and is generally referred to as the Brown-Walker reaction. The over-all anodic process may be represented by... 

Several electrochemically important reactions occur on the surface of oxidized noble metal electrodes without reaction with the surface oxide. The oxide film then behaves as a new type of electrocatalyst surface on which the reaction proceeds, in distinction to the underlying metal. The oxide films are normally only one to three oxygen layers in thickness. The following inorganic reactions are of this class (a) O2 evolution, (b) CI2, (c) Br2 (to a small extent, since adsorbed Br blocks surface oxidation) and N2 evolution (from N3 ) while, in the case of organic reactions, (a) the Kolbe and Crum-Brown/Walker syntheses, as well as (b) the Hofer-Moest reaction, are of this type. ... 

Faraday, in 1834, was the first to encounter Kolbe-electrolysis, when he studied the electrolysis of an aqueous acetate solution [1], However, it was Kolbe, in 1849, who recognized the reaction and applied it to the synthesis of a number of hydrocarbons [2]. Thereby the name of the reaction originated. Later on Wurtz demonstrated that unsymmetrical coupling products could be prepared by coelectrolysis of two different alkanoates [3]. Difficulties in the coupling of dicarboxylic acids were overcome by Crum-Brown and Walker, when they electrolysed the half esters of the diacids instead [4]. This way a simple route to useful long chain l,n-dicarboxylic acids was developed. In some cases the Kolbe dimerization failed and alkenes, alcohols or esters became the main products. The formation of alcohols by anodic oxidation of carboxylates in water was called the Hofer-Moest reaction [5]. Further applications and limitations were afterwards foimd by Fichter [6]. Weedon extensively applied the Kolbe reaction to the synthesis of rare fatty acids and similar natural products [7]. Later on key features of the mechanism were worked out by Eberson [8] and Utley [9] from the point of view of organic chemists and by Conway [10] from the point of view of a physical chemist. In Germany [11], Russia [12], and Japan [13] Kolbe electrolysis of adipic halfesters has been scaled up to a technical process. 

The Kolbe-type reaction has continued to receive much attention with particular emphasis on formic acid oxidation. However, the mechanism remains open to question. The mechanism given primary consideration at present is that originally suggested by Crum-Brown and Walker," who proposed direct electrochemical oxidation of the carboxylate ion with subsequent decomposition of the radicals which combine giving the hydrocarbon. This theory, known as the discharged ion and free radical mechanism, can be... 

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