Soluble oxalates

The common treatment methods are acidification, neutralization, and incineration. When oxahc acid is heated slightly in sulfuric acid, it is converted to carbon monoxide, carbon dioxide, and water. Reaction with acid potassium permanganate converts it to carbon dioxide. Neutralization with alkahes, such as caustic soda, yields soluble oxalates. Neutralization with lime gives practically insoluble calcium oxalate, which can be safely disposed of, for instance, by incineration. 

Quenching of the emissions of fluorophores sensitized by dioxetanes has also been used for chemical analysis [29, 30] but this is probably less specific and less sensitive than direct measurement of the sensitized emission of the analyte. Most analytical reactions of the dioxetanes require an organic solvent for optimal solubility and CL yields [31]. This has led to considerable interest in the development of water-soluble oxalate esters [32],... 

The leaf extract of curry leaf has been reported to contain moisture (66.3%), protein (1%), fat (1%), carbohydrate (16%), fibre (6.4%) and mineral matter (4.2%). The main minerals per 100 g of leaves are calcium (810 mg), phosphorus (600 mg) and iron (2.1 mg). The vitamins in the leaves are carotene (12,600 i.u.), nicotinic acid (2.3 mg) and vitamin C (4 mg) (Anon., 1962 Kumar et al., 1999). The extract also contains oxalic acid, which reduces the availability of calcium. The contents are total oxalate (1.352%) and soluble oxalate (1.155%) (Ananthasamy et al., 1960 Walde et al., 2005). The effects of storage temperature on the nutritive value were studied by Palaniswamy et al. (2002). Reisch et al. (1994a) found the furocou-marins in the seeds. 

SAFETY PROFILE Poisons by ingestion and inhalation. Powerful irritants. Oxalates are corrosive to tissue and produce local irritation. When ingested they have a caustic effect on the mouth, esophagus, and stomach. The soluble oxalates are readily absorbed from the gastrointestinal tract and can cause severe damage to the kidneys. Oxalates are common components of poisonous plants. When heated to decomposition they emit toxic and irritating fumes. See also OXALIC ACID. 

The equilibrium solubilities of the oxalates in water are very small. However, they tend to form supersaturated solutions. This tendency is most pronounced for the magnesium salt, and therefore magnesium iron(III) oxide is the most difficult to prepare. If the precipitations are carried out in acetic acid solution, they can be made nearly quantitative. Metal acetates are the best starting materials because they yield acetic acid as a by-product. Iron(II) acetate is obtained by dissolving pure iron in acetic acid. The solution must be kept out of contact with the air to prevent the formation of iron(III), which gives a soluble oxalate. 

Small amounts of calcium and oxalic acid are then added and the pH is adjusted to approximately 3 to allow formation of an oxalate precipitate. The iron forms a very soluble oxalate, thus remaining in solution. This and two subsequent oxalate precipitations serve to remove any remaining iron. 

The principal source of thorium is monazite (p. 425), a phosphate of cerium and lanthanum with up to 15% of thoria. It is dissolved in concentrated sulphuric acid and the thorium phosphate precipitated with magnesium oxide. The washed phosphate heated with sodium carbonate gives crude thoria, ThOg, which is converted to the soluble oxalate and separated from the insoluble oxalates of cerium and lanthanum. After ignition to oxide the nitrate is made, purified by recrystallisation, and again calcined to thoria. 

Funtumafrine-B (XXX) and funtumafrine-C (XXXI) were obtained from the leaves of Funtumia africana via the soluble oxalates. The IR-spectrum of both alkaloids disclosed the presence of a carbonyl group (1706 cm i) and their structure was established by the preparation from funtuphyllamine-B (furnishing funtumafrine-B) and funtuphyllamine-C (furnishing funtumafrine-C) on chromic acid oxidation 17, 18). 20a-Dimethylamino-5a-pregnan-3-one had been previously reported as a product of partial synthesis 20). 

The soluble oxalates found in rhubarb and most other poisonous plants are readily absorbed from the gastrointestinal tract and lead to systemic formation of calcium oxalate. 

Oxalic acid may have a direct corrosive effect on the eyes, skin, and digestive tract after contact. However, once absorbed (or produced as a result of the metabolism of other compounds), oxalic acid and other soluble oxalates react with calcium in the plasma to form insoluble calcium oxalate. Systemic formation of calcium oxalate may produce hypocalcemia directly. Precipitation of calcium oxalate in the renal system (proximal tubules of the kidney) may lead to local necrosis of the tubular epithelium, producing kidney dysfunction and electrolyte imbalance. Precipitation of calcium oxalate may also occur in the blood vessels, heart, lungs, and liver leading to local effects. 

Soluble oxalates in the leaves are absorbed via the gastrointestinal tract. Once absorbed, oxalates bind with calcium producing secondary hypocalcemia. 

Petrarulo M, CereUi E, Marangella M, Cosseddu D, Vitale C, Linari F. Assay of plasma oxalate with soluble oxalate oxidase. Clin Chem 1994 40 2030-4. 

Precipitation with oxalate at pH 3-4 separates calcium from metals which give soluble oxalate complexes [e.g., Fe(III), Al, and Ti], and also from phosphate. Calcium oxalate can also be precipitated from homogenous solution [11. 

Along with the rare-earth elements. Sc may be separated as the sparingly soluble oxalate or fluoride. Suitable collectors in the oxalate and the fluoride methods are lanthanum and calcium, respectively [14]. 

The precipitation of thorium oxalate with calcium as collector is a much favoured separation method [3]. In a weakly acid medium (pH 1-4) it can be precipitated with oxalic acid. Rare-earth metals and U(IV) are also precipitated, but many metals (e.g., Fe, Al, Ti, Zr, Nb, and Mo) remain in solution as soluble oxalate complexes. 

This brief summary of peroxyoxalate chemiluminescence in no way does justice to the topic and the interested reader is urged to consult the more comprehensive accounts cited in this chapter. If and when water-soluble oxalate esters become readily available, there is no doubt that these labels will be adapted to the types of assay that have formed the main subject matter for this article, viz., immunoassays, nucleic acid and gene probe assays, and clinical chemistry assays. 

Analysis.—In fatal cases of poisoning by oxalic acid the contents of the stomach are sometimes strongly acid in reaction more usually, owing to the administration of antidotes, neutral, or even alkaline. In a systematic analysis the poison is to be sought for in the residue of the portion examined for prussic acid And phosphorus or, if the examination for those substances be omitted, in the residue or final alkaline fluid of the process for alkaloids. If oxalic acid alone is to be sought for, the contents of the stomach, or other substances if acid, are extracted with water, the liquid filtered, the filtrate evaporated, the residue extracted with alcohol, the alcoholic fluid evaporated, the residue redissolved in water (solution No. 1). The portion undissolved by alcohol is extracted with alcohol acidulated wdth hydrochloric. acid, the solution evaporated after filtration, the residue dissolved in water (solution No. 2). Solution No. 1 contains any oxalic acid which may have existed free in the substances examined No. 2 that which existed in the form of soluble oxalates. If lime or magnesia have been administered as an antidote, the substances must be boiled for an hour or two with potassium carbonate (not the hydroxid), filtered, and the filtrate treated as above. In the solutions so obtained, oxalic acid is characterized by the tests given above. The urine is also to be examined microscopically for crystals of calicum oxalate. The stomach may contain small quantities of oxalates as normal constituents of certain foods. 

Rust stain removal involves forming a water soluble oxalate ion complex of iron like pe(C204)3]. The overall reaction is ... 

C. Ingestion of soluble oxalates may result in weakness, tetany, convulsions, and cardiac arrest owing to profound hypocalcemia. The QT interval may be prolonged, and variable conduction defects may occur. Oxalate crystals may be found on urinalysis. Insoluble oxalate crystals are not absorbed but can cause irritation and swelling in the oropharynx and esophagus. 

C. Group 2b plants contain soluble oxalate salts (sodium or potassium) that can produce acute hypocalcemia, renal injury, and other organ damage secondary to precipitation of calcium oxalate crystals in various organs (see p 295). Mucous membrane irritation is rare, allowing patients to ingest sufficient quantities to cause systemic toxicity. Gastroenteritis may also occur. 

Rhubarb (leaves) Rheum rhaponticum 2b Soluble oxalates... 

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