Carboxylate salts, oxidation

Most commercial sorbic acid is produced by a modification of this route. Catalysts composed of metals (2inc, cadmium, nickel, copper, manganese, and cobalt), metal oxides, or carboxylate salts of bivalent transition metals (2inc isovalerate) produce a condensation adduct with ketene and crotonaldehyde (22—24), which has been identified as (5). 

The anodic oxidation of the carboxylate anion 1 of a carboxylate salt to yield an alkane 3 is known as the Kolbe electrolytic synthesis By decarboxylation alkyl radicals 2 are formed, which subsequently can dimerize to an alkane. The initial step is the transfer of an electron from the carboxylate anion 1 to the anode. The carboxyl radical species 4 thus formed decomposes by loss of carbon dioxide. The resulting alkyl radical 2 dimerizes to give the alkane 3 " ... 

Yu, W.W., Falkner, J.C., Yavuz, C.T. and Colvin, V.L. (2004) Synthesis of monodisperse iron oxide nanocrystals by thermal decomposition of iron carboxylate salts. Chemical Communications, (20), 2306-2307. 

The effect of structural variation and the use of different caboxylate salts as cocatalysts was investigated by Pietikainen . The epoxidation reactions were performed with the chiral Mn(III)-salen complexes 173 depicted in Scheme 93 using H2O2 or urea hydrogen peroxide as oxidants and unfunctionalized alkenes as substrates. With several soluble carboxylate salts as additives, like ammonium acetate, ammonium formate, sodium acetate and sodium benzoate, good yields (62-73%) and moderate enantioselectivities (ee 61-69%) were obtained in the asymmetric epoxidation of 1,2-dihydronaphthalene. The results were better than with Ai-heterocycles like Ai-methylimidazole, ferf-butylpyridine. 

While high polymers of /3-lactones can also be formed by cationic polymerization, most of the commercial production seems to be by the anionic route. Carboxylate salts such as sodium acetate or benzoate are commonly the initiators, but other nucleophiles, such as triethylamine, betaine, potassium f-butoxide, aluminum and zinc alkoxides, various metal oxides and tris(dimethylamino)benzylphosphonium chloride (the anion of which is the initiator), are of value. Addition of crown ethers to complex the counter cation increases the rate of reaction. When the reaction is carried out in inert but somewhat polar organic solvents, such as THF or ethyk acetate, or without solvent, chain propagation is very fast and proceeds without transfer reactions. 

In this section, electrodes with relatively pure films of hexacyanoferrate(II/III) salts will be considered. They can be produced by a variety of means. In one series of experiments, graphite electrodes were treated with Fe(CO)5 in a glow discharge, after which the electrode surface contained iron(III) oxides and carboxylates (from oxidation of carbon monoxide). When the electrode is placed in aqueous K4[Fe(CN)6] the [Fe(CN)6]% couple is attached. The film is stable over many thousand electrochemical cycles and colour changes corresponding to those shown in equation (36) are noted. 

The aerobic oxidation of alcohol under neutral or acidic conditions to produce the corresponding adds, which can avoid the neutralization of the carboxylate salts, is also an important R D issue. In Au-catalyzed alcohol oxidation in methanol, the corresponding methyl esters are obtained with high seledivity instead of carboxylic acids by using metal oxide supported Au NPs [157, 160], In this case, base is not necessary, or only a catalytic amount of base is required to promote the readion. However, in water, it was demonstrated that alcohols were not oxidized under acidic conditions [161] and only aldehydes were oxidized to carboxylic adds [162]. Even under solvent-free conditions or in organic solvents, alcohols were converted into aldehydes without base however, the alcohols were not fully oxidized to carboxylic acid under acidic conditions [163-166]. 

Electro-organic chemistry is the study of the oxidation and reduction of organic molecules and ions, dissolved in a suitable solvent, at an anode and cathode respectively in an electrolysis cell, and the subsequent reactions of the species so formed. The first experiment of this type was reported in 1849 by Kolbe, who described the electrolysis of an aqueous solution of a carboxylate salt and the isolation of a hydrocarbon. The initial step involves an anodic oxidation of the carboxylate anion to a radical which then dimerises to the alkane. 

Aromatic aldehydes (and other aldehydes in which a-hydrogen atoms are absent, e.g. formaldehyde and trimethylacetaldehyde) under the influence of strong aqueous or alcoholic alkali undergo simultaneous oxidation and reduction yielding the alcohol and corresponding carboxylate salt. Thus ... 

These are the most favourable of all and the precursors, such as the hydroxy acids, e.g. 15, cannot usually be isolated, though the carboxylate salts are stable. The only important thing is to get the oxidation level of the precursor right. Using cyclic amines as examples, a fully saturated ring 45 would come from an alkylation reaction on 46 X = a leaving group. Imines 47 or enamines 49 would come from aldehydes or ketones 48. 

Several other processes have been developed, however, to accomplish the oxidative decarboxylation of carboxylic acids oxidation by Pb(OAc)4, by iodosobenzene-diacetate, and by Ag(II) salt generated in situ in a catalytic cycle from a variety of peroxides (benzoyl peroxide, percarbonate, perborate) [2] other than the already mentioned peroxydisulfate. Representative examples are shown in Eqs (9)—(12) of Table 2. 

The allylic oxidation of 1,3-dienes catalyzed by Pd(II) complexes in the presence of BQ (added in stoichiometric quantities or used catalytically with a stoichiometric amount of a co-oxidant) leads to the formation of 1,4-oxidation products under mild reaction conditions (at room temperature in AcOH) [42], A very interesting stereochemical aspect arises in 1,4-diacyloxylation reactions of cycloalkenes when carboxylate salts are used as nucleophiles. Although the relative stereochemistry... 

If the reaction mixture becomes warm or too basic, the diketone undergoes oxidative cleavage. The products are the carboxylate salts of carboxylic acids, which can be converted to the free acids by adding dilute acid. 

A test for aldehydes. The Tollens reagent is a silver-ammonia complex Ag(NH3)2 OH]. Tollens reagent oxidizes an aldehyde to a carboxylate salt and deposits a silver mirror on the inside of a glass container, (p. 862)... 

The oxidation of cyclohexane is accompanied by the oxidative degradation of the products. In other words, the products themselves undergo metal-initiated radical chain oxidation. For this reason oxidation is normally carried out at low conversions when the selectivity to the desired products is high. The catalysts used are a mixture of hydrocarbon soluble carboxylate salts of Co2+ and Mn2+ or Cr3+. Due to the better solubility properties, salts of long-chain carboxylic acids such as 2-ethyl hexanoic or naphthenic acids are favored. As already mentioned, the primary role of the metal ions is to act as catalysts for the initiation steps. In other words, the metal ions undergo redox reactions with 8.9 to give 8.10 and 8.11. 

An oxidizing system which uses bromine in the presence of carboxylate salts of nickel(II) has been studied in some detail, and supersedes the analogous procedure which uses dibenzoyl peroxide in the presence of nickel(II) bromide. In some unsymmetrical cases the selectivity is somewhat dependent on... 

Oxidation. This reagent effects the oxidation of primary alcohols to carboxylic acids under alkaline conditions. Exposure of the hydroxy carboxylate salt derived from 1 to sodium ruthenate in 1 (V sodium hydroxide solution afforded the diacid 2, in which the substituent at Ce had epimerized to the thermodynamically favored 8-configuration. ... 

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