Oxalic acid/oxalate production

Group VI Donors. Oxygen donor ligands. A new and more successful preparation of CIS- and tra s-K[Rh(ox)2(H20)2] has been reported, via the chromatographic separation of the acid hydrolysis products from Kj[Rh(ox)3],4j-H20. The u.v.-visible spectra of these complexes cast doubts on the purity of the samples previously described. An interesting feature of Rh -oxalate chemistry is the assertion that K3[Rh(ox)3],4 H20 actually exists as the partly unidentate K6[Rh(ox)3][Rh(ox)2(C204H)(OH)],8H20. This has now... 

Various constituents in plant foods can impede Ca absorption. Plant-based diets can be high in oxalate and phytate, which are recognized as inhibitors of Ca absorption. In fact, Ca absorption is considered to be inversely proportional to oxalic acid content of the food (Weaver et al, 1999). Phytic acid poses Ca absorption problems for those species imable to endogenously synthesize phytase (e.g., humans, birds, and pigs). The Ca in CCM is chelated with the citrate and malate anions, which may make CCM less reactive than other sources of Ca toward food components known to interact with Ca " cations. For example, Lihono et al (1997a) reported data suggesting that the Ca in CCM may be less likely to complex with phytates than other Ca salts. Qn this basis, CCM may be more appropriate for the fortification of soy or other phytic acid-containing products. 

One of the first facts observed in regard to uric acid was that on heating it yielded cyanuric acid, (OCNH)3, and ammonia, NH3. As these same products had been obtained by heating urea, OC(NH2)2, it was considered probable that a urea residue was present in uric acid. It was then shown that on oxidation with lead dioxide, one of the ureids, the di-ureid known as allantoin was obtained, together with urea, oxalic acid and carbon dioxide. With other oxidizing agents, such as nitric acid, the products were equal molecules of urea and the two ureids alloxan and parabanic acid. From alloxan there may be obtained, by reduction, two other ureids, viz., barbituric acid and... 

Oxalic acid is recommended for the hydrolysis of the enol ethers obtained by Birch reduction to give the nonconjugated ketone with a mineral acid the product is the coryugated ketone. - "... 

Morphological studies explain the mechanisms of E-glass corrosion. According to these studies, acid corrosion of E-glass is caused by calcium and aluminum depletion which varies depending on the acid type, fiber type, and acid concentration. Oxalic and sulfuric acids are more corrosive than nitric and hydrochloric acids. This difference is due to the fact that, in oxalic acid, precipitated products are formed which decrease the concentration of leachates in solution. In addition to the loss of mineral content, fibers develop axial and spiral cracks. Crack formation depends on the rate of material depletion. 

Oxalic acid Cleavage Product after cleavage ... 

Fig.2. Oxalic acid. Metabolic sources of oxalate. 2-Hydroxy-3-oxoadipate is a normal excretory product in humans, which diverts glyoxylate from oxalate production (see Inborn errors of metabolism. Oxalosis).

The white form of MF is less pure than the brown form but purer than the gray form. It is produced in presence of cupric chloride (or some other substances such as KCl, ZnCl2, BaCl2, or CU2CI2). In practice copper and hydrochloric acid are added to the dissolving tank containing mercury and nitric acid. Addition of hydrochloric acid itself results in formation of white MF contaminated by oxalic acid. The product is, however, not as clean-white looking and the crystals are not as uniform in shape and size as in the case of combination of copper and hydrochloric... 

With regard to the determination of oxalic acid, see the standardization of potassium permanganate, above.) An interesting extension of the oxidization reaction of oxalic acid is the determination of calcium ions. The latter are precipitated as calcium oxalate in hot acetic acid (solubility product = 10 ). The precipitate is separated out from the solution, washed, and dissolved into a 2 mol/L sulfuric acid solution. After heating, the liberated oxalic acid is titrated with permanganate. In fact, oxalic acid is simply liberated by displacement of the precipitation equilibrium ... 

Crystallizes from water in large colourless prisms containing 2H2O. It is poisonous, causing paralysis of the nervous system m.p. 101 C (hydrate), 189°C (anhydrous), sublimes 157°C. It occurs as the free acid in beet leaves, and as potassium hydrogen oxalate in wood sorrel and rhubarb. Commercially, oxalic acid is made from sodium methanoate. This is obtained from anhydrous NaOH with CO at 150-200°C and 7-10 atm. At lower pressure sodium oxalate formed from the sodium salt the acid is readily liberated by sulphuric acid. Oxalic acid is also obtained as a by-product in the manufacture of citric acid and by the oxidation of carbohydrates with nitric acid in presence of V2O5. 

Glycol gives the non-volatile oxalic acid. After heating the mixture under reflux for 10 minutes, transfer 2 ml. of the cold product to a test-tube and add 4 ml. of cone. H2SO4. Note the production of carbon monoxide and carbon dioxide on heating (p. 350). 

The b.p. under diminished pressure has been given as 80-81°/18 mm. To obtain a very pure sample of the amine, dissolve 1 part (by weight) of the above product with a sohitiuii of 1-04 parts of crystallised oxalic acid in 8 parts of hot water, add a little deculeiirisiiig carbon, and tilter. The liltered solution deposits crystals uf the acid oxalate about o g. of tliis salt remains in each 100 ml. of... 

J-unsaturated ester is formed from a terminal alkyne by the reaction of alkyl formate and oxalate. The linear a, /J-unsaturated ester 5 is obtained from the terminal alkyne using dppb as a ligand by the reaction of alkyl formate under CO pressure. On the other hand, a branehed ester, t-butyl atropate (6), is obtained exclusively by the carbonylation of phenylacetylene in t-BuOH even by using dppb[10]. Reaction of alkynes and oxalate under CO pressure also gives linear a, /J-unsaturated esters 7 and dialkynes. The use of dppb is essen-tial[l 1]. Carbonylation of 1-octyne in the presence of oxalic acid or formic acid using PhiP-dppb (2 I) and Pd on carbon affords the branched q, /J-unsatu-rated acid 8 as the main product. Formic acid is regarded as a source of H and OH in the carboxylic acids[l2]. 

A balanced chemical reaction indicates the quantitative relationships between the moles of reactants and products. These stoichiometric relationships provide the basis for many analytical calculations. Consider, for example, the problem of determining the amount of oxalic acid, H2C2O4, in rhubarb. One method for this analysis uses the following reaction in which we oxidize oxalic acid to CO2. 

Re OPe . The final step in the chemical processing of rare earths depends on the intended use of the product. Rare-earth chlorides, usually electrolytically reduced to the metallic form for use in metallurgy, are obtained by crystallisation of aqueous chloride solutions. Rare-earth fluorides, used for electrolytic or metaHothermic reduction, are obtained by precipitation with hydrofluoric acid. Rare-earth oxides are obtained by firing hydroxides, carbonates or oxalates, first precipitated from the aqueous solution, at 900°C. 

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89). 

The sodium formate process is comprised of six steps (/) the manufacture of sodium formate from carbon monoxide and sodium hydroxide, (2) manufacture of sodium oxalate by thermal dehydrogenation of sodium formate at 360°C, (J) manufacture of calcium oxalate (slurry), (4) recovery of sodium hydroxide, (5) decomposition of calcium oxalate where gypsum is produced as a by-product, and (6) purification of cmde oxahc acid. This process is no longer economical in the leading industrial countries. UBE Industries (Japan), for instance, once employed this process, but has been operating the newest diaLkyl oxalate process since 1978. The sodium formate process is, however, still used in China. 

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