Oxygen decarboxylation

TThe presence of a methyl group on the [1 carbon of a fatty acid makes )3 oxidation impossible, and these branched fatty acids are catabolized in peroxisomes of animal cells by a oxidation. In the oxidation of phytanic acid, for example (Fig. 17-17), phytanoyl-CoA is hydroxylated on its a carbon, in a reaction that involves molecular oxygen decarboxylated to form an aldehyde one carbon shorter, and then oxidized to the... 

In the presence of oxygen, decarboxylation of amino acids is followed by oxidative deamination to an aldehyde due to the action of amine oxidase. The existence of such an enzyme in animal tissues was first observed in 1928 by Hare-Bernheim (76), who used tyramine as substrate and therefore chose the name tyraminase. It was shown later (20) that a great variety of primary, secondary, and tertiary amines was subject to attack by this enzyme and consequently the name amine oxidase or monoamine oxidase. in contrast to diamine oxidase, was introduced. Only amines-with... 

Diacyl Peroxides. Table 3 Hsts several commercial diacyl peroxides and their corresponding 10-h half-hfe temperatures, deterrnined in benzene and other solvents (32). Although diacyl peroxides cleave at the oxygen—oxygen bond, decarboxylation can occur, either simultaneously or subsequentiy (eq. 22) ... 

The extent of decarboxylation primarily depends on temperature, pressure, and the stabihty of the incipient R- radical. The more stable the R- radical, the faster and more extensive the decarboxylation. With many diacyl peroxides, decarboxylation and oxygen—oxygen bond scission occur simultaneously in the transition state. Acyloxy radicals are known to form initially only from diacetyl peroxide and from dibenzoyl peroxides (because of the relative instabihties of the corresponding methyl and phenyl radicals formed upon decarboxylation). Diacyl peroxides derived from non-a-branched carboxyhc acids, eg, dilauroyl peroxide, may also initially form acyloxy radical pairs however, these acyloxy radicals decarboxylate very rapidly and the initiating radicals are expected to be alkyl radicals. Diacyl peroxides are also susceptible to induced decompositions ... 

This ladical-geneiating reaction has been used in synthetic apphcations, eg, aioyloxylation of olefins and aromatics, oxidation of alcohols to aldehydes, etc (52,187). Only alkyl radicals, R-, are produced from aliphatic diacyl peroxides, since decarboxylation occurs during or very shortiy after oxygen—oxygen bond scission in the transition state (187,188,199). For example, diacetyl peroxide is well known as a source of methyl radicals (206). 

Until recent years the only syntheses of 3-hydroxy quinoline involved multistep processes, the last step of which consisted of the conversion of 3-aminoquinoline to 3-hydroxyquinoline via the diazonium salt. " Small quantities of quinoline have been oxidized to 3-hydroxyquinoline in low yields by using oxygen in the presence of ascorbic acid, ethylenediaminetetraacetic acid, ferrous sulfate, and i)hosi)halc buffer. The decarboxylation of 3-hydroxycinchoninic, acid in boiling nitrobenzene has been re-... 

Nilrosated fluoro compounds are frequently prepared by electrophilic nitrosation on an electron-nch center of oxygen, nitrogen, or carbon The preparation of fluorochloronitronitrosomethane from the decarboxylation of fluorochloronitro-acetic acid in nitric acid is unique [f ] (equation 1)... 

In the absence of oxygen, these thiolene-2-ones are rather stable and have been kept at 0°C for several months. 3-Hydroxythiophene, on the other hand, which has been prepared in low yield from 3-thio-phenemagnesium bromide in the same way as the 2-isomer, or through decarboxylation of 3-hydroxy-2-thiophenecarboxylic acid, "" is very unstable. Its IR spectrum indicates that it also exists as a tautomeric mixture largely in its enolic form. ... 

Decarboxylation of isoxazole-3-carboxylic acids is related to the nucleophilic cleavage of the isoxazole ring as far as the nature of the reaction products is concerned. It occurs at temperatures above 200°C and is accompanied by the cleavage of the nitrogen-oxygen bond of the heterocyclic ring to yield a j8-ketonitrile. It was first reported by Claisen with 5-methyl- and 5-phenyl-isoxazole-3-carboxylic acids (153- 154).Under the reaction conditions, j8-ketonitriles condense... 

The approach makes use of a bipyrroledicarbaldehyde 54 and a tripyrranedicarboxylic acid 55 which are condensed with subsequent decarboxylation in the presence of acid and oxygen. The presence of oxygen, as in many other syntheses of porphinoid macrocycles, is necessary to adjust the oxidation level of the chromophore which is in sapphyrins a 2271-aromatic cyclically conjugated system. Many sapphyrins 56 with different substitution patterns have been synthesized according to this general scheme. As in all McDonald-type condensations at least one of the components has to be symmetric because otherwise mixtures of constitutional isomers would be formed. 

In the anodic decarboxylation of phenylacetic acid benzaldehyde is the major product (80%) at low current density (< 3.2mA/cm ). Its formation is supposed to occur by reaction of the intermediate benzyl radical with oxygen, which is possibly simultaneously generated at the anode [31]. 

In the bisdecarboxylation of the cyclobutenedicarboxylic acid 52, products are obtained whose formation possibly involves a cyclobutadiene intermediate [322], A case of a 1,3-bisdecarboxylation has been reported in the preparation of a bicyclobutane (Table 11, No. 26). An elimination, that involves the cleavage of an carbon-oxygen bond after the decarboxylation, has been observed with the carboxylic acid 53 (Eq. 33) [282]. 

Despite its synthetic importance, the mechanism of the copper-quinoline method has been studied very little, but it has been shown that the actual catalyst is cuprous ion. In fact, the reaction proceeds much faster if the acid is heated in quinoline with cuprous oxide instead of copper, provided that atmospheric oxygen is rigorously excluded. A mechanism has been suggested in which it is the cuprous salt of the acid that actually undergoes the decarboxylation. It has been shown that cuprous salts of aromatic acids are easily decarboxylated by heating in quinoline and that arylcopper compounds are intermediates that can be isolated in some cases. Metallic silver has been used in place of copper, with higher yields. ... 

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