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oxalic acid(ŏksăl`ĭk) or
ethanedioic acid(ĕth'āndīōĭk), HO2CCO2H, a colorless, crystalline organic carboxylic acid that melts at 189°C; with sublimation. Oxalic acid and oxalate salts are poisonous. Oxalic acid is found in many plants, e.g., sorrel and rhubarb, usually as its calcium or potassium salts. Oxalic acid is the only possible compound in which two carboxyl groupscarboxyl group
, in chemistry, functional group that consists of a carbon atom joined to an oxygen atom by a double bond and to a hydroxyl group, OH, by a single bond. Carboxylic acids are compounds whose molecules contain a carboxyl group that is joined to a hydrogen atom, an
..... Click the link for more information. are joined directly; for this reason oxalic acid is one of the strongest organic acids. Unlike other carboxylic acids (except formic acidformic acid
or methanoic acid
, HCO2H, a colorless, corrosive liquid with a sharp odor; it boils at 100.7°C; and solidifies at 8.4°C;. It has the lowest molecular weight and is the simplest of the carboxylic acids.
..... Click the link for more information. ), it is readily oxidized; this makes it useful as a reducing agent for photography, bleaching, and ink removal. Oxalic acid is usually prepared by heating sodium formate with sodium hydroxide to form sodium oxalate, which is converted to calcium oxalate and treated with sulfuric acid to obtain free oxalic acid.
HOOC—COOH, the simplest dibasic carboxylic acid. A colorless crystalline compound, oxalic acid has a melting point of 189.5°C. Its solubility in water is 10 g per 100 g H2O at 20°C and 120 g at 100°C. Oxalic acid is poorly soluble in alcohol and ether and is insoluble in benzene and chloroform. It is a relatively strong acid (K125 = 3.6 × 10–2). It forms the hydrate C2H2O42H2O (melting point, 101.5°C), as well as acid and neutral salts (oxalates), esters, amides, and other derivatives.
Salts of oxalic acid are found in plants—for example, its acid potassium salt is found in sorrel (genus Oxalis, hence the name). The acid forms in tissues as a metabolic product and, together with the oxalic acid in food, is excreted with urine as potassium oxalate. Oxalates participate in the formation of stones in the kidneys and urinary bladder in cases of disorders of mineral metabolism. Oxalic acid is formed in oxalic acid fermentation.
Oxalic acid was first synthesized in 1842 by F. Wöhler from cyanogen. It is produced industrially by the pyrolysis of sodium formate, HCOONa. It is used as mordant in cloth printing; it is also used in the production of dyes and inks, as a bleaching agent, and as a precipitating agent for rare earths.