Decarboxylation, of organic acids

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... 

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... 

The decarboxylation of organic acids in water requires AC = — 2d io — 40 cal.deg." (Johnson and Moelwyn-Hughes, 1940a), in agreement with several earlier reports. No interpretation has yet been offered. 

Micro-amounts of carboxyl groups in individual compounds are determined by pyrolytic decarboxylation of organic acids via pyrolysis in a helium atmosphere in the presence of copper carbonate and quinoline accompanied by liberation of an equivalent amount of carbon dioxide [143]. The determination of carboxylic groups by heating the sample to 385°C without reagents has been described [144]. Whyte and Engler... 

Radical decarboxylation of organic acids to the corresponding noralkane with tri- -butyltin hydride or r-butylmercaptan ... 

The end product CO2 arises vnOwut any considerable change in energy by decarboxylation of organic acids. 

It can be seen in Fig. 8 that the high concentrations of acetic acid in oilfield brines (activities typically from 10 to 10 ", see below) are preserved metastably with respect to the decarboxylation reaction. In other words, if stable equilibrium was reached in sedimentary basin brines, concentrations of acetic acid would be several orders of magnitude lower than they are. Similar results can be obtained for propanoic acid with the data in Table 3. This disequilibrium with respect to the decarboxylation reaction indicates that large kinetic barriers to decarboxylation of organic acids exist under sedimentary basin conditions. 

If this sequence of carbonate reactions is coupled with parallel organic reactions, including generation and decarboxylation of organic acids and acid anions, a predictive, process-oriented model can be constructed for the carbonate reactions. The model consists of three operations (1) interpretation of reaction pathways (2) kinetic modeling of organic reactions and (3) simulation of rock/water interactions in either time or temperature space. Integrating these three operations allows us to predict zones of carbonate dissolution or optimum porosity enhancement (positive porosity anomalies) in source/reservoir rock systems. 

Decarboxylation of organic acid anions (i.e., alkalinity dominated by organic acid anions with elevated PC02) Decarboxylation and/or abiotic thermal sulfate reduction... 

A large variety of organic oxidations, reductions, and rearrangements show photocatalysis at interfaces, usually of a semiconductor. The subject has been reviewed [326,327] some specific examples are the photo-Kolbe reaction (decarboxylation of acetic acid) using Pt supported on anatase [328], the pho-... 

This is the decarboxylation of a (3-keto acid which undergoes smoothly even in the absence of an enzyme. Thus, it can be said that the mother nature utilizes an organic reaction with a low activation energy. The second step of the decarboxylation is the conversion of a-ketoglutaric acid to succinic acid (Fig. 3). This is the same type of reaction as the decarboxylation of pyruvic acid. 

Recently, researchers have detected 2,5-dimethylfuran and 2-methylfuran and normal alkanes in kerogen of the 2.7 x 109 year old Belingwe, Rhodesia stromatolites, by the method of pyrolysis/ GC/MS [26]. They concluded that although furans could probably be derived from many compounds, their probable origin is in bacterial and algal sugars, and that the alkanes are either products of decarboxylation of fatty acids or unaltered constituents of ancient organisms. 

Histamine is synthesized in tissues by decarboxylation of amino acid L-histidine, a process catalyzed by the pyridoxalphosphate-dependent enzyme L-histidinedecarboxylase. Histamine can enter the organism with food it also can be generated by bacteria of the gastrointestinal tract. However, these sources do not create additional reserves of histamine since exogenous histamine is easily catabolized in the organism. 

A third early mechanism for enzymic processes involves the formation of imines between the amino group of a lysine residue on an enzyme and the carbonyl group of a substrate, followed by standard imine chemistry. The first example concerned the decarboxylation of acetoacetic acid (Hamilton and Westheimer, 1959). The mechanism was based on the non-enzymic physical organic chemistry of Kai Pedersen (Pedersen, 1934). He postulated that the catalysis by aniline of the decarboxylation of dimethylacetoacetic acid proceeds by a mechanism parallel to that shown in Scheme 7 for acetoacetic acid itself (Pedersen, 1938). 

Simple carboxylic acids suffer photo-Kolbe decarboxylation under the usual photoelectrochemical conditions. In fact, this reaction type was one of the first characterized examples of oxidative cleavage of an organic molecule induced by long w avelength irradiation of a semiconductor. In the decarboxylation of acetic acid at... 

Three separate and distinct methods have been utilized for the determination of aconitic acid in sugar cane and/or sorghum products. One involves the extraction of aconitic acid from the sample with an organic solvent, the second is based upon the decarboxylation of aconitic acid while the third employs the polarographic technique.5 ... 

This procedure is a modification of one recently described in the literature.3 The first step is based on early work of Fittig 4 and Volhard5 as modified by Spencer and Wright.2 The third step, ring closure of a 7-haloketone, is well known.5-6 Dicyclopropyl ketone was reported to form in small amounts from the decarboxylation of cyclopropanecarboxylic acid over thoria,7 but there is some doubt3 about the product. Dicyclopropyl ketone is available in research quantities from the Aldrich Chemical Company, Milwaukee 12, Wisconsin, and from Columbia Organic Chemicals, Inc., Columbia, South Carolina. 

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. 

As discussed above, the spatial separation of these processes in C4 plants necessitates a degreee of structural organization in the form of Kranz anatomy. CAM plants do not show such anatomy but have other specializations because the temporal separation of the synthesis and decarboxylation of C4 acids requires storage of large amounts of C4 acids in the vacuole. 

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