1,1-Dicarboxylic acids, decarboxylation

Lumazine-6-carboxylic acid, 7-hydroxy-tautomerism, 3, 271 Lumazine-7-carboxylic acid synthesis, 3, 304 Lumazine-6,7-dicarboxylic acid decarboxylation, 3, 304 reactions, 3, 304 synthesis, 3, 320 Lumazine-6,7-dione catabolism, 3, 322... 

Pyrimidine-4,5-dicarbonitrile, 2-methyl-faydrolysis, 3, 83, 84 Pyrimidine-4,5-dicarboxylic acid synthesis, 3, 76, 122 Pyrimidine-4,6-dicarboxylic acid decarboxylation, 3, 80... 

Tetrazine-3,6-dicarboxylic acids decarboxylation, 3, 555 electronic spectra, 3, 540... 

Dicarboxylic acids decarboxylate by attack of peroxy radicals on a-C— H bonds. The evidence for such a mechanism was obtained from data on the decarboxylation of adipic acid, with COOH and COOD groups, in oxidizing cumene, when the velocities of C02 production were found to be the same [299]. Carbon dioxide is produced from the acid in the initiated oxidation of cumene (Table 14) and cyclohexanol [215] after the induction period associated with the formation of an intermediate, probably a-hydroperoxide, after attack of peroxy radicals on a-C—H... 

In the synthesis of the keto acid just given, the dicarboxylic acid decarboxylates in a PRACTICE PROBLEM 18.9... 

The existence of the n-C2 to n-C4 mono- and dicarboxylic acids in hydro-thermal sedimentary environments depends upon the rates of their production and the rates of decomposition and/or oxidation. These two classes of acids exhibit very different rates and mechanisms of decarboxylation. Decarboxylation of acetic acid, and probably of other aliphatic monocar-boxylic acids, proceeds by a heterogeneous catalytic mechanism apparently very different from the homogeneous mechanism for decarboxylation of the dicarboxylic acids. Due to the limited amount of experimental information regarding the kinetics of oxidation or condensation for both classes of acids, no definitive mechanistic trends can be postulated for this process. Nevertheless, it is possible to place constraints on the kinetics and mechanism for the oxidation reaction(s) if this process were assumed to control the ultimate decomposition of acetic acid. Results from studies of mono- and dicarboxylic acid decarboxylation are summarized below. 

When cinnamaldehyde, succinic acid and acetic anhydride are heated in the presence of litharge (PbO), the aldehyde and the succinic acid condense to give the dicarboxylic acid (I), which undergoes decarboxylation to give the pale yellow crystalline 1,8-diphenyloctatetrene (II), Kuhn has shown that as the... 

The procedure (with ethylene dibromide replacing trimethyleiie dibromide) described for cycZobutanecarboxylic acid (previous Section) does not give satisfactory results when applied to the cyclopropane analogue the yield of the cyclopropane-1 1 dicarboxylic acid is considerably lower and, furthermore, the decarboxylation of the latter gives a considerable proportion (about 30 per cent.) of butyrolactone ... 

Regioselectivity of C—C double bond formation can also be achieved in the reductiv or oxidative elimination of two functional groups from adjacent carbon atoms. Well estab llshed methods in synthesis include the reductive cleavage of cyclic thionocarbonates derivec from glycols (E.J. Corey, 1968 C W. Hartmann, 1972), the reduction of epoxides with Zn/Nal or of dihalides with metals, organometallic compounds, or Nal/acetone (seep.lS6f), and the oxidative decarboxylation of 1,2-dicarboxylic acids (C.A. Grob, 1958 S. Masamune, 1966 R.A. Sheldon, 1972) or their r-butyl peresters (E.N. Cain, 1969). 

Thiazole carboxylic acid (70), R, - Rj = H, can be also obtained from decarboxylation of 2,5-thiazole dicarboxylic acids. 

Section 19 17 11 Dicarboxylic acids (malonic acids) and p keto acids undergo thermal decarboxylation by a mechanism m which a p carbonyl group assists the departure of carbon dioxide... 

Table 2. Decarboxylation Temperatures and Molar Heats of Combustion of Dicarboxylic Acids...

Practically all pyridazine-carboxylic and -polycarboxylic acids undergo decarboxylation when heated above 200 °C. As the corresponding products are usually isolated in high yields, decarboxylation is frequently used as the best synthetic route for many pyridazine and pyridazinone derivatives. For example, pyridazine-3-carboxylic acid eliminates carbon dioxide when heated at reduced pressure to give pyridazine in almost quantitative yield, but pyridazine is obtained in poor yield from pyridazine-4-carboxylic acid. Decarboxylation is usually carried out in acid solution, or by heating dry silver salts, while organic bases such as aniline, dimethylaniline and quinoline are used as catalysts for monodecarboxylation of pyridazine-4,5-dicarboxylic acids. 

The best way to make pyrimidine in quantity is from 1,1,3,3-tetraethoxypropane (or other such acetal of malondialdehyde) and formamide, by either a continuous (58CB2832) or a batch process (57CB942). Other practical ways to make small amounts in the laboratory are thermal decarboxylation of pyrimidine-4,6-dicarboxylic acid (744), prepared by oxidation of 4,6-dimethylpyrimidine (59JCS525), or hydrogenolysis of 2,4-dichloropyrimidine over palladium-charcoal in the presence of magnesium oxide (53JCS1646). 

The degradation of more complex substances can be regarded as another route to pteridine derivatives. Already in 1895 tolualloxazine was oxidized by alkaline permanganate to lumazine-6,7-dicarboxylic acid, and further heating led in a stepwise decarboxylation to lumazine (3) (1895CB1970). 

Imidazole-4,5-dicarboxylic acid, 1-methyl-decarboxylation, 5, 435 Imidazole-4,5-dicarboxylic acid anhydride synthesis, 5, 435... 

Imidazole-4,5-dicarboxylic acids, coupling, 5, 403 decarboxylation, 5, 434 1-substituted synthesis, 5, 468 synthesis, 5, 362, 402, 484 Imidazole-4,5-dione, l-alkyl-2-phenyl-synthesis, 5, 129, 479 Imidazole-2,4-diones tautomerism, 5, 370 Imidazole-4,5-diones tautomerism, 5, 370 Imidazole-2,4-dithione, 5,5-diphenyl-tautomerism, 5, 370 Imidazole-2,4-dithiones tautomerism, 5, 370 Imidazolepropanol synthesis, 5, 486 Imidazoles accelerators epoxy resins, 1, 407... 

Claisen ester condensation, 6, 279 Thiazolecarboxylic acid chlorides reactions, 6, 279-280 Thiazolecarboxylic acid hydrazides synthesis, 6, 280 Thiazolecarboxylic acids acidity, 6, 279 decarboxylation, 6, 279 reactions, S, 92 6, 274 Thiazole-2-carboxylic acids decarboxylation, S, 92 Thiazole-4-carboxylic acids stability, S, 92 Thiazole-5-carboxylic acids decarboxylation, S, 92 Thiazole-4,5-dicarboxylic acid, 2-amino-diethyl ester reduction, 6, 279 Thiazole-4,5-dicarboxylic acids diethyl ester saponification, 6, 279 Thiazolediones diazo coupling, 5, 59 Thiazoles, 6, 235-331 ab initio calculations, 6, 236 acidity, S, 49 acylation, 6, 256 alkylation, S, 58, 73 6, 253, 256 analytical uses, 6, 328 antifogging agents... 

TROST - CHEN Decarboxylation Ni complex catalyzed decarboxylation of dicarboxylic acid anbydndes to form alkenes. 

Compartmentation of these reactions to prevent photorespiration involves the interaction of two cell types, mescrphyll cells and bundle sheath cells. The meso-phyll cells take up COg at the leaf surface, where Og is abundant, and use it to carboxylate phosphoenolpyruvate to yield OAA in a reaction catalyzed by PEP carboxylase (Figure 22.30). This four-carbon dicarboxylic acid is then either reduced to malate by an NADPH-specific malate dehydrogenase or transaminated to give aspartate in the mesophyll cells. The 4-C COg carrier (malate or aspartate) then is transported to the bundle sheath cells, where it is decarboxylated to yield COg and a 3-C product. The COg is then fixed into organic carbon by the Calvin cycle localized within the bundle sheath cells, and the 3-C product is returned to the mesophyll cells, where it is reconverted to PEP in preparation to accept another COg (Figure 22.30). Plants that use the C-4 pathway are termed C4 plants, in contrast to those plants with the conventional pathway of COg uptake (C3 plants). 

---