Organic acid decarboxylation

While experimental studies of organic acid decarboxylation have established some of the controls, the relevance experimentally determined rate constants for natural systems, where potential catalysts of many types abound, is questionable. Field calibrations clearly are advantageous from the standpoint of eliminating the effects of kinetic artifacts, but other Kmitations exist. In trying to relate the effects of time and temperature on decarboxylation rates in natural systems, the effects that variations in the type and abundance of organic matter can have on the production of organic acids, and therefore on their primary concentration, must be minimized. 

The model results discussed above express only the effects time and temperature on organic acid production from kerogen, and the effect of porosity on organic acid concentrations. They do not account for the effects of time and temperature on organic acid decarboxylation. Therefore, the results are best applied to Neogene and source rocks where the field data discussed earlier indicate that decarboxylation effects on total acetate concentrations are small, where temperatures do not exceed approximately 150 C. 

Whereas experimental studies of organic acid decarboxylation have established some of the controls, the relevance of experimentally determined rate constants for natural systems, where potential catalysts of many types abound, is questionable. Field calibrations clearly are advantageous from... 

Comparison of thermodynamic calculations for organic acid decarboxylation reactions with observations from nature and results of laboratory experiments provides an illustration of the application of stable equilibrium calculations to identify the magnitude of kinetic barriers. The law of mass action expression for the acetic acid decarboxylation reaction [Eq. (5)] is given by... 

Several investigators have studied the kinetics of reaction (5) and other organic acid decarboxylation reactions as functions of temperature and fluid composition, as well as in the presence of minerals, which may catalyze the reaction (Kharaka et al. 1983 Drummond and Palmer 1986 Palmer and Drummond 1986 Schleusener et al. 1987, 1988 Crossey 1991). Early... 

The physical properties of cyanoacetic acid [372-09-8] and two of its ester derivatives are Hsted ia Table 11 (82). The parent acid is a strong organic acid with a dissociation constant at 25°C of 3.36 x 10. It is prepared by the reaction of chloroacetic acid with sodium cyanide. It is hygroscopic and highly soluble ia alcohols and diethyl ether but iasoluble ia both aromatic and aUphatic hydrocarbons. It undergoes typical nitrile and acid reactions but the presence of the nitrile and the carboxyUc acid on the same carbon cause the hydrogens on C-2 to be readily replaced. The resulting malonic acid derivative decarboxylates to a substituted acrylonitrile ... 

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. 

Wasserman, H.H. in Newman Steric Effects in Organic Chemistry, Wiley NY, 1956, p. 352. See also Buchanan, G.L. Kean, N.B. Taylor, R. Tetrahedron, 1975, 31, 1583. StericaUy hindered P-keto acids decarboxylate more slowly Meier, H. Wengenroth, H. Lauer, W. Krause, V. Tetrahedron Lett., 1989, 30, 5253. 

Deoxygenation by full decarboxylation is the best route to make fuel precursors from bio-oil, because paraffin is produced and expensive hydrogen is not required. Decarboxylation of bio-oil has been tried over zeolites, yielding an aromatic product with a too low yield and excessive coke formation (Section 6.9.3). Selective decarboxylation of organic acids makes the bio-oil less acidic and corrosive. If acids can be removed selectively as CO2, it would also improve the energy... 

Thiamine diphosphate (ThDP) is an important cofactor in many enzymes which either transfer carbon units between molecules or decarboxylate organic acids. 

Similarly to C2042 coreactant oxidative decarboxylation of organic acids R—C02 produces a strong reductant R ... 

Chemoselecti vity could potentially be achieved if the oxidation potential of a desired donor adsorbate lies between the valence band edges of two possible semiconductor photocatalysts. Since TiOj has a more positive valence band edge than does CdS, it should be the more active photocatalyst. Consistent with this idea, decarboxylation of organic acids, Eq. (5), is much more efficient on irradiated suspensions of rutile than of CdS... 

A number of materials,10 water, certain organic acids, the most important of which is citric acid, and certain inorganic salts, interfere with the determination. The decarboxylation cannot be conducted in the presence of nitrates and when carbonates are present two separate determinations of carbon dioxide are necessary. The procedure is also inapplicable when oxidizing compounds which are soluble in the hot reagent are present. Another interfering substance, sulfur dioxide,01 can be eliminated by the use of a saturated, acidified (sulfuric acid) solution of potassium dichromate to wash the gases evolved by the decarboxylation procedure. 

As a biogenic amine, dopamine belongs to a group of substances produced in the organism by decarboxylation of amino acids. Besides dopamine and norepinephrine formed from it, this group includes many other messenger molecules such as histamine, serotonin, and y-aminobutyric acid. 

Calcium hydroxide shows a strong selectivity for benzene [34], In a steam atmosphere the PET is hydrolyzed and after that the resulting TPA is decarboxylated by the catalyst. At 700°C 36% of the PET can be converted into benzene. This corresponds to a benzene yield of 88% based on PET. Other main prodncts are carbon oxides and char. Organic acids are not observed (Eignre 25.15). 

Olefinic esters may be obtained directly by the Knoevenagel reaction. Alkyl hydrogen malonates are used in place of malonic acid. Decarboxylation then gives the ester directly as in the preparation of ethyl 2-heptenoate (78%) and methyl m-nitrocinnamate (87%). Alkyl hydrogen malonates are readily available by partial hydrolysis of dialkyl malonates. The use of malonic ester in the condensation leads to olefinic diesters, namely, alkylidenemalonates such as ethyl heptylidenemalonate (68%). A small amount of organic acid is added to the amine catalyst since the salts rather than the free amines have been shown to be the catalysts in condensations of this type. Various catalysts have been studied in the preparation of diethyl methylenemalonate. Increased yields are obtained in the presence of copper salts. Trimethylacetalde-hyde and malonic ester are condensed by acetic anhydride and zinc chloride. Acetic anhydride is also used for the condensation of furfural and malonic ester to furfurylidenemalonic ester (82%). ... 

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