Oxalate decarboxylation and

In Oxalobacter formigenes, oxalate and its decarboxylation product formate form a one-to-one antiport system, which involves the consumption of an internal proton during decarboxylation, and serves as a proton pump to generate ATP by decarboxylative phosphorylation (Anantharam et al. 1989). 

At higher temperatures, carbon dioxide, formic acid, oxalic acid, glycolic acid, hydroxymalonic acid, glyceric acid, and other acids were shown to be formed. The formation of carbon dioxide is ascribed to decarboxylation of 38 oxalic acid and D-erythronic acid arise from cleavage of the C-2-C-3 bond compound 39 is cleaved to glyoxylic acid plus D-erythronic acid. Compound 40 is oxidized further to D-g7ycero-2,3-pentodiulosonic acid and is subsequently cleaved to oxalic and glyceric acids. 

Oxalate viologen ion pair complexes have been examined in detail under pulsed laser flash and continuous photolysis [205], As the photolysis leads to the oxidation of oxalate dianion, the strongly reducing CO 2"is formed after decarboxylation and a second MV2 + is reduced, generating another equivalent of MV +. Malonate, succinate, glutarate, polyacrylate and polymethacrylate were also tested and found to be effective as CTC donors for MV + formation. In the case of malonate, decomposition of the carboxylate was not accompanied by MV2 + consumption. This was attributed to the efficiency of a back electron transfer step following immediately the decarboxylation [206]. 

Fig. 12.5. The two main processes identified that lead to the precipitation of calcium carbonate from an oxalate source in oxalotrophic bacteria, the formate and the glyoxylate pathways. TCA, tricarboxylic acid cycle GA, glyoxyhc acid cycle EPS, exopolysaccharides 1, oxalate decarboxylation into formate 2, formate dehydrogenation permease/transporters.

Decarboxylation of D-er /hexulosonic acid (3), gives D-erj/iliro-pentulosonic acid (6), which, in turn, provides D- l2/cero-2,3-pentodiulosonic acid, the latter subsequently being cleaved to oxalic acid and glyceric acid. D-erythro-Hexos-2,3-diulose (5), in similar fashion, yields glyoxylic acid and d-erythronic acid. 

The following sequence of dipositive metal ions shows a decreasing effect on the rate of decarboxylation of oxaloacetic acid Cu(II), Zn(II), Co(II), Ni(II), Mn(II), Cu(II) (91). The rate constants for these decarboxylations approximately parallel the formation constants of the corresponding metal oxalates. A similar result was found in the decarboxylation of acetonedicarboxylic acid in the presence of certain transition metal ions the decarboxylation rates paralleled the formation constants of the metal malonates (170). These parallelisms indicate that the effectiveness of a metal ion in these decarboxylation reactions depends on its ability to chelate with the oxalate ion and the malonate ion, which resemble the transition states of the oxaloacetic and acetonedicarboxylic acids, respectively. 

Pyran-4-one, mp 32°C, is a colourless, crystalline compound. It forms a hydrochloride with HCl, mp 139°C. 4//-Pyran-4-one is prepared by decarboxylation of chelidonic acid 12. This is made by a,a -diacylation of acetone with oxalic ester and proceeds via the acid-catalyzed cyclization of the triketo compound 13 ... 

Oxalic acid poses a problem to both leafy plants and vertebrates because these organisms cannot catabolize it [108]. Although accumulation of oxalate leads to stress in plants, in vertebrates this molecule can be metaboHzed by bacteria present in the intestinal tract [109]. Oxalate can be catabolized in different ways by oxidation, by decarboxylation of oxalyl-coenzyme A or by direct decarboxylation. Both oxidation and decarboxylation of oxalate are catalyzed by Mn-containing enzymes. Here we will discuss the oxalate decarboxylate reaction that produces formate and CO2. The crystal structure of oxalate oxidase from Bacillus subtilis... 

The dicarboxylic acids found in basin brines (i.e., oxalic, malonic, and succinic) are expected to be less stable under hydrothermal conditions than monocarboxylic acids of comparable chain lengths. The stability of these acids has been discussed previously to the extent that structural factors make a-, and y-carboxyl acids susceptible to homogeneous decarboxylation. The mechanisms for decarboxylation of jff-carboxyl acids and their derivatives in solvents of varying polarity have been especially well studied and the results are believed to be generally applicable to a- and y-carboxyl acids as well (Clark 1969). For this reason, the following detailed discussion of the mechanism for homogeneous decarboxylation of dicarboxylic acids is based primarily on malonic acid. Finally, oxidation of dicarboxylic acids may be predicted, although the process has not been well studied. 

Enthalpies and entropies of activation for the decarboxylation of oxalic, malonic, and acetic acids are listed in Table 1 and are shown separately on the isokinetic plots in Fig. 8. Linear trends are observed for (1) aqueous acetic acid and sodium acetate in the presence of various catalysts (2) aqueous oxalic acid at several pH values (3) oxalic acid in different solvents and (4) malonic acid in different solvents and in aqueous solutions having a different pH. Note that the isokinetic trend for the decarboxylation of malonic acid in aqueous solutions at various pH is identical to that for the reaction in nonaqueous solvents, i.e., there is one isokinetic trend for malonic acid. Moreover, the effect of pH on the activation parameters for the decarboxylation of malonic acid in aqueous solution is minimal. On the other hand, the activation data for the decarboxylation of oxalic acid in aqueous solutions determined by Crossey (1991) do not follow the same isokinetic trend as do the corresponding data for this reaction in other solvents. By contrast, activation data calculated from the rate constants determined by Dinglinger and Schroer (1937) for oxalic acid in water (pH 0.5) fall on the isokinetic trend set by the decarboxylation of oxalic acid in nonaqueous solvents, as well as the rate data determined by Lapidus et al. (1964) in the vapor phase. The cause of the disparity between the isokinetic relationships determined by Crossey (1991) and the remainder of the oxalic acid results requires further investigation. The reaction could have been surface-catalyzed, but this is doubtful because some of the oxalic acid... 

Fig. 8. Isokinetic plots for the decarboxylation of a malonic and b oxalic acids. Activation data for acetic acid are plotted for spatial reference. Filled and partially filled symbols represent aqueous systems. Linear least-squares fits to acetic acid, acetate, and the combined remaining data are given by the dashed, dotted, and solid lines, respectively. Note that with the exception of Crossey s (1991) results, the data for malonic and oxalic acids would superimpose. The data are given in Table 1. The acids and sources are as follows A, malonic (Richardson and O Neal 1972) A, malonic (Hall 1949) O, oxalic (Richardson and O Neal 1972) , oxalic (Crossey 1991) O, oxalic (Dinglinger and Schroer 1937, 1938 Lutgert and Schroer 1940) oxalic vapor (Lutgert and Schroer 1940) 0, dideuterio-oxalic (Lutgert and Schroer 1940) 0, dideuterio-oxalic vapor (Lapidus et al. 1966a,b) C, dideuterio-oxalic in D2O (Lutgert and Schroer 1940) B, acetic (Bell et al. 1993) , sodium acetate (Bell et al. 1993) and gallic (Boles et al. 1988). A more detailed version of this plot appears in Bell et al. (1993)...

The ligand-free palladium-catalysed coupling of aryl iodides and bromides with potassium oxalate monoester results in a decarboxylation reaction yielding aromatic esters such as (112). Carbon-hydrogen substitution is involved in the decarboxylative acylation reaction of cyclic enamides with a-oxocarboxylic acids, which may yield acylated enamides such as (114). The reaction is likely to involve a cyclic vinylpalladium intermediate (113) which, after decarboxylation and reductive elimination yields the acylated product. ... 

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