Calcium oxalate

Calcium oxalate
Names

IUPAC name calcium ethanedioate
Identifiers
CAS Number	25454-23-3 (anhydrous)^Y 5794-28-5 (monohydrate)^N
ChEBI	CHEBI:60579^Y
ChemSpider	30549^Y
Jmol interactive 3D	Image
PubChem	16212978
InChI InChI=1S/C2H2O4.Ca/c3-1(4)2(5)6;/h(H,3,4)(H,5,6);/q;+2/p-2^Y Key: QXDMQSPYEZFLGF-UHFFFAOYSA-L^Y InChI=1/C2H2O4.Ca/c3-1(4)2(5)6;/h(H,3,4)(H,5,6);/q;+2/p-2 Key: QXDMQSPYEZFLGF-NUQVWONBAM
SMILES C(=O)(C(=O)[O-])[O-].[Ca+2]
Properties
Chemical formula	CaC₂O₄
Molar mass	128.097 g/mol, anhydrous 146.112 g/mol, monohydrate
Appearance	white solid
Density	2.12 g/cm³, anhydrous 2.12 g/cm³, monohydrate
Melting point	200 °C (392 °F; 473 K) decomposes (monohydrate)
Solubility in water	0.67 mg/L (20 °C)
Related compounds
Other cations	Beryllium oxalate Magnesium oxalate Strontium oxalate Barium oxalate Radium oxalate Iron(II) oxalate Iron(III) oxalate
Related compounds	Oxalic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is ^YN ?)
Infobox references

Scanning electron micrograph of the surface of a kidney stone showing tetragonal crystals of Weddellite (calcium oxalate dihydrate) emerging from the amorphous central part of the stone (the horizontal length of the picture represents 0.5 mm of the figured original)

Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula CaC₂O₄. It is a chemical compound that forms envelope-shaped crystals, known in plants as raphides. A major constituent of human kidney stones, calcium oxalate is also found in beerstone, a scale that forms on containers used in breweries.

Occurrence

Calcium oxalate is a poisonous substance that can produce sores and numbing on ingestion and may even be fatal. Many plants accumulate calcium oxalate as it has been reported in more than 1000 different genera of plants.^[1] The calcium oxalate accumulation is linked to the detoxification of calcium (Ca²⁺) in the plant.^[2]

The poisonous plant dumb cane (Dieffenbachia) contains the substance and on ingestion can prevent speech and be suffocating. It is also found in rhubarb (in large quantities in the leaves) and in species of Oxalis, Araceae, taro, kiwifruit, tea leaves, agaves, Virginia creeper (Parthenocissus quinquefolia), and Alocasia and in spinach in varying amounts. Plants of the Philodendron genus contain enough calcium oxalate that consumption of parts of the plant can result in uncomfortable symptoms. Insoluble calcium oxalate crystals are found in plant stems, roots, and leaves and produced in idioblasts.

Calcium oxalate, as 'beerstone', is a brownish precipitate that tends to accumulate within vats, barrels and other containers used in the brewing of beer. If not completely removed in a cleaning process, beerstone will leave an unsanitary surface that can harbour microorganisms.^[3] Beerstone is composed of calcium and magnesium salts and various organic compounds left over from the brewing process; it promotes the growth of unwanted microorganisms that can adversely affect or even ruin the flavour of a batch of beer.

Calcium oxalate crystals in the urine are the most common constituent of human kidney stones, and calcium oxalate crystal formation is also one of the toxic effects of ethylene glycol poisoning.

Hydrated forms of the compound occur naturally as three mineral species: whewellite (monohydrate, known from some coal beds), weddellite (dihydrate) and a very rare trihydrate called caoxite.

Medical significance

Morphology and diagnosis

Calcium oxalate exists in monohydrate and dihydrate forms, which can be distinguished by the shape of the respective crystals.

Calcium oxalate dihydrate crystals are octahedral. A large portion of the crystals in a urine sediment will have this type of morphology, as they can grow at any pH and naturally occur in normal urine.
Calcium oxalate monohydrate crystals vary in shape, and can be shaped like dumbbells, spindles, ovals, or picket fences, the last of which is most commonly seen due to ethylene glycol poisoning.^[4] This latter form is what investigators discovered in the kidneys of two victims that ultimately led to the successful prosecution and conviction of murderer Lynn Turner, who poisoned both her husband and boyfriend with ethylene glycol-based antifreeze.^[5]

Urine microscopy showing calcium oxalate crystals in the urine. The octahedral crystal morphology is clearly visible.
Urine microscopy showing a calcium oxalate monohydrate crystal (dumbbell shaped) and a calcium oxalate dihydrate crystal (envelope shaped) along with several erythrocytes.
Urine microscopy showing several calcium oxalate monohydrate crystals (dumbbell shaped, some of them clumped) and a calcium oxalate dihydrate crystal (envelope shaped) along with several erythrocytes.

Kidney stones

Main article: Kidney stone § Diagnosis

About 80% of kidney stones are partially or entirely of the calcium oxalate type. They form when urine has been persistently acidic. Some of the oxalate in urine is produced by the body. Calcium and oxalate in the diet play a part, but are not the only factors that affect the formation of calcium oxalate stones. Dietary oxalate is an organic ion found in many vegetables, fruits, and nuts. Calcium from bone may also play a role in kidney stone formation.

Effects of ingestion

Even a small dose of calcium oxalate is enough to cause intense sensations of burning in the mouth and throat, swelling, and choking that could last for up to two weeks.^[6] In greater doses it can cause severe digestive upset, breathing difficulties, coma or even death. Recovery from severe oxalate poisoning is possible, although permanent liver and kidney damage might have occurred by this time.

The stalks of plants in the Dieffenbachia genus produce the most severe oxalate reactions. The needle-like oxalate crystals produce pain and swelling when they contact lips, tongue, oral mucosa, conjunctiva, or skin. Edema primarily is due to direct trauma from the needle-like crystals and, to a lesser extent, by other plant toxins (e.g., bradykinins, enzymes).

Depending on the plant ingested, mild (Elephant Ear Colocasia esculenta) to more severe (Jack in the Pulpit, Arisaema) can cause compromised airways. One bite on the Arisaema seed pod will result in immediate swelling and burning. It takes over 12 hours for the swelling to subside.

Treatment
Medication administered at the emergency room may include diphenhydramine, epinephrine, or famotidine, all intravenously.^[7]

Industrial applications

Calcium oxalate is used in the manufacture of ceramic glazes.^[8]

References

↑ Francesci, V.R.; Nakata (2005). "Calcium oxalate in plants: formation and function". Annu Rev Plant Biol (56): 41–71.
↑ Martin, G; Matteo Guggiari; Daniel Bravo; Jakob Zopfi; Guillaume Cailleau; Michel Aragno; Daniel Job; Eric Verrecchia; Pilar Junier (2012). "Fungi, bacteria and soil pH: the oxalate–carbonate pathway as a model for metabolic interaction". Environmental Microbiology 14 (11): 2960–2970. doi:10.1111/j.1462-2920.2012.02862.x.
↑ Johnson, Dana (23 March 1998). "Removing Beerstone". Modern Brewery Age. Birko Corporation R&D. Retrieved 2007-08-06.
↑ "Urine Crystals". https://ahdc.vet.cornell.edu/. Cornell University. Retrieved 12 July 2014. External link in |website= (help)
↑ Nash, Alanna. "The Black Widow Killer: Two men. Two murders. Too many questions.". Reader's Digest. Retrieved 2009-04-26.
↑ Outbreak of Food-borne Illness Associated with Plant Material Containing Raphides. Informa Healthcare.
↑ "Toxicity of the genus Dieffenbachia". Toxicology and Applied Pharmacology 15: 38–45. doi:10.1016/0041-008X(69)90129-X.
↑ "CALCIUM OXALATE HUMMEL CROTON". Hummel Croton Inc. Retrieved 2012-05-02.