Decarboxylation of carboxylate ions

Spontaneous decarboxylations of carboxylate ions and hydrolyses of aryl phosphate dianions and aryl sulfate monoanions are much faster in organic solvents than in water (Thomson, 1970 Kemp and Paul, 1970 Bunton et al., 1967 Kirby and Varvoglis, 1967). This solvent effect is consistent with the Hughes-Ingold qualitative solvent theory because these reactions involve dispersion of charge in forming the transition state. 

Decarboxylations can be regarded as reversals of the addition of carbanions to carbon dioxide (6-32), but free carbanions are not always involved.471 When the carboxylate ion is decarboxylated, the mechanism can be either SeI or Se2. In the case of the SeI mechanism, the reaction is of course aided by the presence of electron-withdrawing groups, which stabilize the carbanion.472 Decarboxylations of carboxylate ions can be accelerated by the addition of a suitable crown ether, which in effect removes the metallic ion.473 The reaction without the metallic ion has also been performed in the gas phase.474 But some acids can also be decarboxylated directly and, in most of these cases, there is a cyclic, six-center mechanism ... 

One-electron oxidation of carboxylate ions generates acyloxy radicals, which undergo decarboxylation. Such electron-transfer reactions can be effected by strong one-electron oxidants, such as Mn(HI), Ag(II), Ce(IV), and Pb(IV) These metal ions are also capable of oxidizing the radical intermediate, so the products are those expected from carbocations. The oxidative decarboxylation by Pb(IV) in the presence of halide salts leads to alkyl halides. For example, oxidation of pentanoic acid with lead tetraacetate in the presence of lithium chloride gives 1-chlorobutane in 71% yield ... 

Electrolysis of carboxylate ions, which results in decarboxylation and combination of the resulting radicals, is called the Kolbe reaction or the Kolbe electrosynthesis. 

The second important class of reducing agents is generated by means of oxidative decarboxylation of carboxylic acids. Electrochemical oxidation of oxalate ion C2042 produces, in aqueous as well as in acetonitrile solutions containing Ru... 

Electrolysis of carboxylate ions, which results in decarboxylation and combination of the resulting radicals, is called the Kolbe reaction. 30 It is used to prepare symmetrical RR, where R is straight- or branched-chained, except that little or no yield is obtained when there is a branching. The reaction is not successful for R = aryl. Many functional groups... 

The persulfate ion S2OI-, with or without various transition metal ions, is a particularly effective oxidant, especially for the decarboxylation of carboxylic acids.535 In the presence of silver(I), persulfate oxidation to silver(II) readily occurs and for aliphatic carboxylic acids the decarboxylation mechanism given in Scheme 4 has been established. The aliphatic radicals produced may then disproportionate, abstract hydrogen or be further oxidized to an alcohol. In... 

Many oxidations (e.g., of oxalate) by the peroxodisulfate ion are catalyzed by Ag+ ion, and the kinetics are best interpreted by assuming initial oxidation to Ag2+, which is then reduced by the substrate. Decarboxylation of carboxylic acids are also promoted by Ag11 complexes, such as (18-I-IX) and others. 

The nucleophilic radicals formed by the silver-catalyzed, oxidative decarboxylation of carboxylic acids by peroxydisulfate ions attack protonated imidazoles mainly at the 2-... 

Radical substitution reactions include alkylations and arylations in the main. Nucleophilic radicals produced by the silver-catalyzed oxidative decarboxylation of carboxylic acids (by peroxydisulfate ion) attack proton-ated azoles at the most electron-deficient sites.Thus, imidazole and 1-alkylimidazoles are methylated exclusively at C-2 in rather low yields. The use of isopropyl and t-butyl radicals gives improved yields, but benzyl and acyl radicals tend to dimerize rather than substitute the... 

Experimental variables affecting the course of the electrolytic decarboxylation of carboxylic acids are summarized in Table 2. For the Kolbe dimerization, the conditions specified for a one-electron process are recommended otherwise the reaction through carbenium ion (non-Kolbe reaction) may occur predominantly. It should be emphasized that even under the conditions most favorable for the Kolbe dimerization, the cation-derived products are usually formed to some extent or, in particular cases, as a major product, depending on the structure of the employed carboxylic acid. 

Free radicals have been generated by decarboxylation of carboxylic acids in the presence of silver ion. The resulting radicals reacted with pyridazines 205 to yield 206, which are intermediates in herbicide and fungicide synthesis (86USP4628088). 

A classic reaction involving electron transfer and decarboxylation of acyloxy radicals is the Kolbe electrolysis, in which an electron is abstracted from a carboxylate ion at the anode of an electrolysis system. This reaction gives products derived from coupling of the decarboxylated radicals. 

When carboxylate ions are decarboxylated, the mechanism is entirely different, being of the Sgl type. Evidence for this mechanism is that the reaction is first order and that electron-withdrawing groups, which would stabilize a carbanion, facilitate the reaction." ... 

Decarboxylations can be regarded as reversals of the addition of carbanions to carbon dioxide (16-33), but free carbanions are not always involved. When the carboxylate ion is decarboxylated, the mechanism can be either Sgl or Se2. In the... 

Energy-resolved CID can be used to measure bond dissociation energies directly, and therefore is readily applicable for the determination of ion affinities. However, Graul and Squires have also described a method for measuring gas-phase acidities using CID of carboxylates. ° Upon CID, carboxylate ions, RCO2, undergo decarboxylation to form the alkyl anions, R, ... 

These enzymes catalyse the non-hydrolytic cleavage of bonds in a substrate to remove specific functional groups. Examples include decarboxylases, which remove carboxylic acid groups as carbon dioxide, dehydrases, which remove water, and aldolases. The decarboxylation of pyruvic acid (10.60) to form acetaldehyde (10.61) takes place in the presence of pyruvic decarboxylase (Scheme 10.13), which requires the presence of thiamine pyrophosphate and magnesium ions for activity. 

A semisystematic study into the hydrolysis of ethyl indole-2-carboxylate in aqueous media at high temperature, indicated that decarboxylation of the resultant acid proceeded by an arenium ion mechanism and was inhibited by base. As base pro-... 

These hydrophobic ammonium ions exert a medium effect on spontaneous, unimolecular reactions. Tri-n-octylmethylammonium chloride effectively speeds decarboxylation of 5-nitrobenzisoxazole carboxylate ion (24) (Kunitake et al., 1980), and tri-n-octyl ethylammonium mesylate or bromide... 

One of the earliest reports on the use of dendrimers in catalysis is the unimolecu-lar decarboxylation of 6-nitro-benzisoxazole-3-carboxylate in the presence of a dendrimer comprising ether dendrons which are functionalized at their periphery with tetra-alkylammonium cations (e.g. 20, Scheme 21) [30]. In aqueous media, the quaternary ammonium groupings promote the reactivity of organic anions which presumably bind in high concentration to the polycationic periphery of the dendrimer. The latter species enhances the rate of the bimolecular hydrolysis of p-nitrophenyl diphenyl phosphate catalyzed by o-iodosobenzoate ion. 

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