Calcium oxalate
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From Wikipedia, the free encyclopedia
Calcium oxalate
Structure of calcium oxalate dihydrate
Calcium, Ca
Carbon, C
Oxygen, O
Hydrogen, H
Names
Preferred IUPAC name
Calcium oxalate
Systematic IUPAC name
Calcium ethanedioate
Other names
Oxalate of lime
Identifiers
CAS Number 5794-28-5 (monohydrate)
25454-23-3 (dihydrate)
192389-49-4 (trihydrate)
3D model (JSmol) Interactive image
ChEBI CHEBI:60579
ChEMBL ChEMBL3184709
ChemSpider 30549
ECHA InfoCard 100.008.419
EC Number 209-260-1
KEGG C17478
PubChem CID 16212978
UNII 4PP86KK527 (monohydrate)
CompTox DTXSID6027214
Dashboard (EPA)
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InChI
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SMILES
Properties
Chemical formula CaC2O4
Molar mass 128.096 g·mol−1
Appearance colourless or white crystals (anhydrous
and hydrated forms)
Density 2.20 g/cm3, monohydrate[1]
Melting point 200 °C (392 °F; 473 K) decomposes
(monohydrate)
Solubility in water 0.61 mg/(100 g) H2O (20 °C)[2]
Solubility 2.7 × 10−9 for CaC2O4[3]
product (Ksp)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards Harmful, Irritant
GHS labelling:
Pictograms
Signal word Warning
Hazard statements H302, H312
Precautionary P280
statements
NFPA
704 (fire diamond)
2
1
1
Safety data External SDS
sheet (SDS)
Related compounds
Other anions Calcium carbonate
Calcium acetate
Calcium formate
Other cations Sodium oxalate
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).
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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 or Ca(COO)2. It
forms hydrates CaC2O4·nH2O, where n varies from 1 to 3. Anhydrous and all
hydrated forms are colorless or white. The monohydrate CaC2O4·H2O occurs
naturally as the mineral whewellite, forming envelope-shaped crystals, known in
plants as raphides. The two rarer hydrates are dihydrate CaC2O4·2H2O, which
occurs naturally as the mineral weddellite, and trihydrate CaC2O4·3H2O, which
occurs naturally as the mineral caoxite, are also recognized. Some foods have high
quantities of calcium oxalates and can produce sores and numbing on ingestion
and may even be fatal. Cultural groups with diets that depend highly on fruits and
vegetables high in calcium oxalate, such as those in Micronesia, reduce the level
of it by boiling and cooking them.[4][5] They are a constituent in 76% of human kidney
stones.[6] Calcium oxalate is also found in beerstone, a scale that forms on
containers used in breweries.
Occurrence
[edit]
Many plants accumulate calcium oxalate as it has been reported in more than 1000
different genera of plants.[7] The calcium oxalate accumulation is linked to the
detoxification of calcium (Ca2+) in the plant.[8] Upon decomposition, the calcium
oxalate is oxidised by bacteria, fungi, or wildfire to produce the soil nutrient calcium
carbonate.[9]
The poisonous plant dumb cane (Dieffenbachia) contains the substance and on
ingestion can prevent speech and be suffocating. It is also found
in sorrel, rhubarb (in large quantities in the leaves), cinnamon, turmeric and in
species of Oxalis, Araceae, Arum italicum, taro, kiwifruit, tea leaves, agaves,
Virginia creeper (Parthenocissus quinquefolia), and Alocasia and in spinach in
varying amounts. Plants of the genus Philodendron 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. Vanilla plants exude calcium oxalates upon
harvest of the orchid seed pods and may cause contact dermatitis.
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
removed in a cleaning process, beerstone will leave an unsanitary surface that can
harbour microorganisms.[10] 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.
Chemical properties
[edit]
Calcium oxalate is a combination of calcium ions and the conjugate base of oxalic
acid, the oxalate anion. Its aqueous solutions are slightly basic because of the
basicity of the oxalate ion. The basicity of calcium oxalate is weaker than that
of sodium oxalate, due to its lower solubility in water. Solid calcium oxalate hydrate
has been characterized by X-ray crystallography. It is a coordination
polymer featuring planar oxalate anions linked to calcium, which also has
water ligands.[1]
