Diacids decarboxylation

The diphenyl ester of the diacid [XI] is used to prevent side reactions such as decarboxylation. 

The temperature at which decarboxylation occurs is of particular interest in manufacturing processes based on polymerisation in the molten state where reaction temperatures may be near the point at which decomposition of the diacid occurs. Decarboxylation temperatures are tabulated in Table 2 along with molar heats of combustion. The diacids become more heat stable at carbon number four with even-numbered acids always more stable. Thermal decomposition is strongly influenced by trace constituents, surface effects, and other environmental factors actual stabiUties in reaction systems may therefore be lower. 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

The cationic pathway allows the conversion of carboxylic acids into ethers, acetals or amides. From a-aminoacids versatile chiral building blocks are accessible. The eliminative decarboxylation of vicinal diacids or P-silyl carboxylic acids, combined with cycloaddition reactions, allows the efficient construction of cyclobutenes or cyclohexadienes. The induction of cationic rearrangements or fragmentations is a potent way to specifically substituted cyclopentanoids and ring extensions by one-or four carbons. In view of these favorable qualities of Kolbe electrolysis, numerous useful applications of this old reaction can be expected in the future. 

Pyruvic acid is not stable at ambient temperature when it is stored for a long period of time. It can only be stored in a refrigerated room. A bottle of this acid was stored in a laboratory at 25°C and detonated, probably because of the overpressure created by the formation of carbon dioxide. Indeed, with diacids and complex acids the decomposition is made by decarboxylation. In this particular case, this decomposition should give rise to acetaldehyde. It could be asked whether, in the exothermic conditions of this decomposition, a polymerisation of this aldehyde (see Aldehydes-ketones on p.310) did not make the situation worse. 

Decarboxylative condensations of this type are sometimes carried out in pyridine, which cannot form an imine intermediate, but has been shown to catalyze the decarboxylation of arylidene malonic acids.215 The decarboxylation occurs by concerted decomposition of the adduct of pyridine to the a, 3-unsaturated diacid. 

A reaction mechanism with Fe304 as catalyst has been proposed [68], in agreement with previous work concerning decarboxylation of acids in the presence of a metal oxide [83]. After the transient formation of iron(II) and iron(III) carboxylates from the diacid and Fe304 (with elimination of water), the thermal decarboxylation of these salts should give the cyclic ketone and regeneration of the catalyst. 

The preparation described here of 3-cyclopentene-1-carboxylic acid from dimethyl malonate and cis-1,4-dichloro-2-butene is an optimized version of a method reported earlier3 for obtaining this often used and versatile building block.6 The procedure is simple and efficient and requires only standard laboratory equipment. 3-Cyclopentene-1-carboxylic acid has previously been prepared through reaction of diethyl malonate with cis-1,4-dichloro(or dibromo)-2-butene in the presence of ethanolic sodium ethoxide, followed by hydrolysis of the isolated diethyl 3-cyclopentene-1,1-dicarboxylate intermediate, fractional recrystallization of the resultant diacid to remove the unwanted vinylcyclopropyl isomer, and finally decarboxylation.2>7 Alternatively, this compound can be obtained from the vinylcyclopropyl isomer (prepared from diethyl malonate and trans-1,4-dichloro-2-butene)8 or from cyclopentadiene9 or cyclopentene.10 In comparison with the present procedure, however, all these methods suffer from poor selectivity, low yields, length, or need of special equipment or reagents, if not a combination of these drawbacks. 

While much attention has been paid to the chemistry of cyclodextrin complexes in solution, there have been relatively few studies of their solid-state reactions. One such reaction is the decarboxylation of phenylethylmalonic acid, 155. In solution this is catalyzed by fj-cyclodextrin, and yields racemic 2-phenylbutyric acid, 156 (230). The malonic acid forms a crystalline 1 1 complex with p-cyclodextrin in which decarboxylation occurs at a much lower temperature than in the crystalline diacid. Interestingly, the product formed in the clathrate reaction is nonracemic, the optical yield being 7%. 

Hydrolysis of the methyl ester and decarboxylation at C-18 occur only under forcing conditions. Alkaline hydrolysis of the C-18 ester of vinblastine requires refluxing m 5 N sodium hydroxide for several hours to give the diacid (18), and ammonialysis of this position in anhydrous methanol is accomplished in a sealed vessel at 100°C for 60 hr to yield the 18 -decarbomethoxy-4-deacetylvinblastine amide (19) (55). Bisindole derivatives lacking the C-22 carboxyl have also been prepared by coupling the vindoline portion with an appropriately chosen ibogane precursor (Section V,G) (54). 

Decarboxylation of 1,1-diacids (ge i-diacids) is a similar reaction involving a hydrogen-bonded transition state. 1,1-Diacids may be stable entities, e.g. 

Table 9.5. Anodic decarboxylation of vic-diacids to form alkenes in pyridine, water containing triethylamine.

Reaction of 1,2 -dicarboxylic acids has been used for the formation of a number of strained alkenes and also applied to the Diels-Alder addition products from maleic anhydride (Table 9.5). Both cis- and tr s-diacids take part in the process. Aqueous pyridine containing, triethylamine as a strong base, is considered the best solvent and higher yields are obtained at temperatures of around 80 "C [130]. Use of a divided cell avoids a possibility of electrocatalytic hydrogenation of the product at the cathode. The addition of /a/-butylhydroquinone as a radical scavenger prevents polymerization of the product [127], An alternative chemical decarboxylation process is available which uses lead tetraacetate [131] but problems can arise because of reaction between the alkene and lead tetraacetate. 

Analogous reactions involving the more reactive iminium ions have also been observed. For example, a lupinine synthesis involved (203) as a reactive intermediate (60JA502). The decarboxylation of. the diacid was relatively nonstereospecific giving, after reduction, a mixture of ( )-lupinine and ( )-epilupinine. 

Controlled hydrolysis of the cyano groups of 58 can give any one of the three possible products the diacid 85, the amide/acid 87, or the diamide 88 in excellent yields (72GEP2216925). Decarboxylation of 87 to 3,5-diamino-6-carbamoylpyrazine (89), and its subsequent conversion to 3,5-diaminopyra-zinoic acid (90) by hydrolysis has also been demonstrated. 

The chemistry of dicarboxylic acids depends on the value of n. See Problem 16.18 for decarboxylations of oxalic acid (n =0) and malonic acid (n = 1). When n = 2 or 3, the diacid forms cyclic anhydrides when heated. When n exceeds 3, acyclic anhydrides, often polymers, are formed. 

Decarboxylation temperatures much lower than those used above have been reported. For example, treatment of diisopropyl 3,3-dimethoxycyclobutane-l, 1-dicarboxylate with 20% hydrochloric acid resulted in decarboxylation of the in situ formed diacid 2 at 100°C (reflux) to give 3-oxocyclobutanecarboxylic acid (3) in 97% yield.2... 

Hence, Stobbe-like condensation with dimethyl-isopropylidene malonate and saponification of malonic acid, half-esters afforded the corresponding 14-carboxyretinoic acids, as a mixture of all E and 9Z isomers (80/20). The all E diacid was easily removed by crystallization from MeCN or ether, Fig. (36). A stereospecific decarboxylation in 2,6-dimethylpyridine led to isotretinoin. 

Asymmetric synthesis is any synthesis that produces enantiomerically or diastereomeri-cally enriched products. This is the expected result if enantiomerically enriched chiral substrates are employed. Of interest here are asymmetric syntheses where the reactants are either achiral or chiral but racemic. Many examples of this type are collected in volumes edited by Morrison [33]. The first example of an asymmetric synthesis involved use of the chiral, optically pure base brucine in a stereoselective decarboxylation of a diacid with enantiotopic carboxyl groups [34] ... 

With vicinal diacids, the occurrence of mono- or bis-decarboxylation could be controlled by light flux. At low light flux, the primary product is monodecarboxylation, as is consistent with ideas described earlier for photoelectrochemical current control, Eq. (28)... 

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