Oxalic acid

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Oxalic acid
Image:Oxalic acid.PNG
Chemical name	ethanedioic acid
Chemical formula	C₂H₂O₄
Molecular mass	90.03 g/mol
CAS number	[144-62-7]
Density	1.77 g/cm³
Boiling point	157 °C subl.
pK_a	1.27 4.27
SMILES	OC(=O)C(O)=O
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Oxalic acid (IUPAC name: ethanedioic acid, formula H₂C₂O₄) is a dicarboxylic acid with structure (HOOC)-(COOH). Because of the joining of two carboxyl groups, this is one of the strongest organic acids. It is also a reducing agent. The anions of oxalic acid as well as its salts and esters are known as oxalates.

1 Biological hazards
2 Role as an organometallic
3 Food science
4 Industrial and household applications
5 Other uses
6 External links

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Biological hazards

Oxalic acid and oxalates are mild nephrotoxic acids that are abundantly present in many plants, most notably fat hen (lamb's quarters), rhubarb and sorrel. Oxalic acid irritates the lining of the gut when consumed, and can prove fatal in large doses. The LD50 for pure oxalic acid is predicted to be about 375 mg/kg body weight, or about 25 g for a 65 kg human. Oxalic acid can also be present in the body due to the consumption of another toxin, ethylene glycol (generally known as automobile antifreeze), because over time, the body metabolizes ethylene glycol into oxalic acid. Bodily oxalic acid may also be synthesized via the metabolism of either glyoxylic acid or unused ascorbic acid (vitamin C), which is a serious health consideration for long term megadosers of vitamin C supplements.

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Role as an organometallic

Oxalic acid also combines with metals such as calcium in the body to form oxalate crystals which further irritate the gut and kidneys. The most common kind of kidney stone is made of calcium oxalate. Image:Oxalicacid.PNG Because it binds vital nutrients such as calcium, long-term consumption of foods high in oxalic acid can lead to nutrient deficiencies. Healthy individuals can safely consume such foods in moderation, but those with kidney disorders, gout, or rheumatoid arthritis are typically advised to avoid foods high in oxalic acid or oxalates.

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Food science

Foods that contain significant concentrations of oxalic acid include (in decreasing order): buckwheat, star fruit (carambola), black pepper, parsley, poppy seed, rhubarb, spinach, chard, beets, banana, cocoa, chocolate, most nuts, most berries, and beans. In the case of rhubarb the only edible portion is the stalk because the root and leaves contain dangerously high concentrations of oxalic acid. The gritty feel one gets in the mouth when drinking milk with rhubarb desserts is caused by precipitation of calcium oxalate. Thus even dilute amounts of oxalic acid can readily "crack" the casein found in various dairy products.

Leaves of the tea plant (Camellia sinensis) are known to contain among the greatest measured concentrations of oxalic acid relative to other plants. However the infusion beverage typically contains only low to moderate amounts of oxalic acid per serving, due to the small mass of leaves used for brewing.

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Industrial and household applications

In addition to its natural occurrence in plants, oxalic acid may also be found in household chemical products such as Bar Keeper's Friend, some bleaches, and rustproofing treatments. It is also used in wood restorers where the acid dissolves away a layer of dry surface wood to expose fresh material underneath.

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