Synthesis of oxalates

A typical example is the synthesis of oxalic acid. Electrochemical synthesis of oxalic acid by reduction of C02 in aprotic media with a Zn sacrificial anode was brought to pilot scale by the Dechema Institute some years ago (1981) [177]... 

Carbonates are often formed as by-products even in the synthesis of oxalates or acrylates. The catalytic system for such a synthesis does not require the presence of palladium, however, since it can be achieved by using only copper salts as catalysts. 

Calcium oxalate results from the reaction of oxalic acid and calcium ions (McNair, 1932), and oxalic acid itself is an effective deterrent to herbivores in its own right (Amott and Webb., 1983). At least four different biochemical pathways have been shown to result in the synthesis of oxalate in plants (Raven et al., 1982). Utilizing radiocarbon-labeled ascorbic acid administered to roots of Yucca torreyi L. (Torrey s yucca) the incorporation into vacuole crystal bundles demonstrated that ascorbate is an important precursor to oxalate in this plant (Horner et ai, 2000). 

A remarkable synthesis of oxalate salts using a supercritical mixture of CO2 and CO under very drastic conditions (400 bar, 380°C) in the presence of solid 082(003) was reported [71]. Friedel-Crafts-type alkylations on zeolites [72] or other solid acid catalysts [73] have been studied using SCCO2 as the medium. Performing the reaction in the supercritical state was found to be superior to either liquid or gas phase processes. Using scCOj lead to enhanced catalyst life-... 

Nickolov, Z.S., Paruchuri, V., Shah, D.O. and Miller, J.D. (2004) FTIR-ATR studies of water structure in reverse micelles during the synthesis of oxalate precursor nanoparticles. Colloids Surf. A Physicochem. Eng. Aspects, 232, 93-99. 

We shall refer again to this important metabolite when considering the endogenous synthesis of oxalic acid. 

Scheme 4J-4 Synthesis of oxalate from CO2 and CO under supercritical conditions.

Scheme 1 Synthesis of oxalic acid and urea without a vis vitalis by Wohler.

B. OXALATE SYNTHESIS BY CARBONYLATIVE OXIDATION B.i. Synthesis of Oxalates in Liquid Phase... 

Synthesis of oxalic acid from cyanogen Wohler... 

Vice versa, the homo C-C coupling of two radical anions with antiparallel spin of the electron localized on C produces the oxalate anion [B], The e -transfer to free CO2 has been attempted for the synthesis of oxalates, with alternate fortune [34]. Whether the homo-coupling or the hetero-coupling is favoured depends on several parameters such as the solvent, the current density, and the electrode. 

Enzymes, apparently unrelated to the malic enzyme or to Utter s oxalacetic carboxylase, catalyzing the decarbmqrlation of oxalacetate, are present in bacteria and certain plant tissues. Some of these enzymes, including the highly purified oxalacetic carboxylase (decarboxylase) of Microeoceus lysodeikticm (152), can catalyze an incorporation of CO in oxalacetate which does not require ATP (236) the mechanism of this incorporation is unknown. Kalten-bach and Kalnitsky (198,199) have reported a net synthesis of oxal-... 

It has been reported that approximately 25% of the dietary intake of ascorbate is excreted as oxalate this would account for about 40% of the total urinary excretion of oxalate. However, there is no known metabolic pathway for the synthesis of oxalate from ascorbate, and it is likely that all or most of the oxalate found in urine after loading doses of ascorbate is formed nonenzymically, after the urine has been collected. Even in people at risk of forming oxalate renal stones it is unlikely that normal or... 

ROOC—COOH, are not. The dialkyl esters are characterized by good solvent properties and serve as starting materials in the synthesis of many organic compounds, such as pharmaceuticals, agrochemicals, and fine chemicals (qv). Among the diesters, dimethyl, diethyl, and di- -butyl oxalates are industrially important. Their physical properties are given in Table 7. 

Primary synthesis of arylazopyrimidines is used (52JCS3448). It is exemplified in the condensation of phenylazomalondiamidine with diethyl oxalate to give the azopyrimidine (833) (66JCS(C)226). Finally, 5-phenylazopyrimidine may be made by the condensation of pyrimidin-5-amine with nitrosobenzene (5UCS1565) but the reaction seems to have been overlooked for many years. 

An early synthesis of pyrido[3,4-6]quinoxalines involved cyclization by strong heating of o-aminoanilinopyridinamine derivatives, e.g. (418) to give (419) (49JCS2540). In a related reaction, o-nitroanilinopyridines (420) were cyclized to pyrido-[2,3-6]- or -[3,4-6]-quinoxa-lines (421) by reduction with iron(II) oxalate, probably via a nitrene intermediate (74JCS(P1)1965). 

In general, imines are too reactive to be used to protect carbonyl groups. In a synthesis of juncusol, however, a bromo- and an iodocyclohexylimine of two identical aromatic aldehydes were coupled by an Ullman coupling reaction modi-fied by Ziegler. The imines were cleaved by acidic hydrolysis (aq. oxalic acid, THF, 20°, 1 h, 95% yield). Imines of aromatic aldehydes have also been prepared... 

From their structures, it appears that the hydrolytic stability of macrocyclic lactones must necessarily be inferior to macrocyclic polyethers. Ease of synthesis of the cyclic esters is therefore one of the aspects which commend them to interest. It is probably for this reason that such lactones have not been made more often by the interesting approach of Kdgel and Schroder . These workers report the ozonolysis of dibenzo-18-crown-6 in a mixture of methanol and dichloromethane at —20°. Reduction of the ozon-ide at —75° using dimethylsulfide followed by warming and addition of acetone led to formation of 6 in 14% yield. The bis-oxalate had mp 164—165° from acetone, very similar to that of the starting crown. The transformation is illustrated below in Eq. (5.9). 

Jongen, N., Lemaitre, J., Bowen, P. and Hofmann, H., 1999. Aqueous synthesis of mixed yttrium-barium oxalates. Chemistry of Materials, 11, pp. 712-718. 

In 1897, Reissert reported the synthesis of a variety of substituted indoles from o-nitrotoluene derivatives. Condensation of o-nitrotoluene (5) with diethyl oxalate (2) in the presense of sodium ethoxide afforded ethyl o-nitrophenylpyruvate (6). After hydrolysis of the ester, the free acid, o-nitrophenylpyruvic acid (7), was reduced with zinc in acetic acid to the intermediate, o-aminophenylpyruvic acid (8), which underwent cyclization with loss of water under the conditions of reduction to furnish the indole-2-carboxylic acid (9). When the indole-2-carboxylic acid (9) was heated above its melting point, carbon dioxide was evolved with concomitant formation of the indole (10). 

Synthesis of 9-oxo-11 CH,1 Sol-bis-(2-tetrahydropyranytoxy)-16,16-dimethyl-prosta-trans-2, trans-13-dienoicacid 4gof ethyl 9a-hydroxy-1 la,1 5a-bis-(2-tetrahydropyranyloxy )-16,16-dimethyl-prosta-trans-2,trans-13-dienoate were dissolved In 130 ml of a mixture of ethanol-water (3 1), mixed with 3.9 g of potassium hydroxide and stirred at 25°C for 2 hours. The reaction mixture was acidified with aqueous solution of oxalic acid to pH 5, and diluted with 100 ml of water, extracted with ethyl acetate. The extracts were washed with water, dried over sodium sulfate and concentrated under reduced pressure to obtain 3,88 g of 90 -hydroxy-11a,15a-bis-(2-tetrahydropyranyloxy)-16,16-dimethyl-prosta-trans-2,trans-13-dienoic acid. 

From a prachcal standpoint, formic acid or its salts are the least valuable reaction products. The energy content of formic acid upon its reverse oxidation to CO2 is insignificant, and its separation from the solutions is a labor-consuming process. At present, maximum effort goes into the search for conditions that would ensure purposeful (with high faradaic yields) synthesis of methanol, hydrocarbons, oxalic acid, and other valuable products. 

Type Ilbd pyrrole syntheses fall into three general categories (1) Hinsberg-type (2) azomethine ylide cycloadditions and (3) isocyanide-based cyclocondensations. The Hinsberg pyrrole synthesis, the cyclocondensation between iminodiacetates and oxalates, has been further exploited in the total synthesis of the lamellarins <06T594,06TL3755>. 

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