Calcium pyrophosphate (Ca2P2O7) is a chemical compound, an insoluble calcium salt containing the pyrophosphate anion. There are a number of forms reported: an anhydrous form, a dihydrate, Ca2P2O7·2H2O and a tetrahydrate, Ca2P2O7·4H2O. Deposition of dihydrate crystals in cartilage are responsible for the severe joint pain in cases of calcium pyrophosphate deposition disease (pseudo gout) whose symptoms are similar to those of gout.[1] Ca2P2O7 is commonly used as a mild abrasive agent in toothpastes,[citation needed] because of its insolubility and nonreactivity toward fluoride.[2]
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Names | |
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IUPAC name
Calcium diphosphate
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Other names
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Identifiers | |
3D model (JSmol)
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ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.029.292 |
E number | E450(vi) (thickeners, ...) |
MeSH | Calcium+pyrophosphate |
PubChem CID
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
Ca2O7P2 | |
Molar mass | 254.053 g/mol |
Appearance | White powder |
Density | 3.09 g/cm3 |
Melting point | 1,353 °C (2,467 °F; 1,626 K) |
insoluble | |
Solubility | soluble in HCl, nitric acids |
Refractive index (nD)
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1.585 |
Hazards | |
NFPA 704 (fire diamond) | |
Flash point | Non-flammable |
Related compounds | |
Other anions
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Calcium phosphate |
Other cations
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Magnesium pyrophosphate Sodium pyrophosphate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation
editCrystals of the tetrahydrate can be prepared by reacting sodium pyrophosphate, Na4P2O7 with calcium nitrate, Ca(NO3)2, at carefully controlled pH and temperature:[3]
- Na4P2O7(aq)+2 Ca(NO3)2(aq)→ Ca2P2O7·4 H2O + 4 NaNO3
The dihydrate, sometimes termed CPPD, can be formed by the reaction of pyrophosphoric acid with calcium chloride:[citation needed]
- CaCl2 + H4P2O7(aq) → Ca2P2O7·2 H2O + HCl.
The anhydrous forms can be prepared by heating dicalcium phosphate:[citation needed]
- 2 CaHPO4 → Ca2P2O7 + H2O
At 240-500 °C an amorphous phase is formed, heating to 750 °C forms
Structure of anhydrous and hydrated forms
editThe stable tetrahydrate was originally reported to be rhombohedral but is now believed to be monoclinic. Additionally there is an unstable monoclinic form.[3]
The dihydrate is triclinic, with hydrogen bonding between the two water molecules and hydrogen bonds to the O atoms on the anion.[citation needed] An hexagonal dihydrate has also been reported.[4]
The anhydrous form has 3 polymorphs,
References
edit- ^ Calcium Pyrophosphate Deposition Disease at eMedicine
- ^ Klaus Schrödter; Gerhard Bettermann; Thomas Staffel; Friedrich Wahl; Thomas Klein; Thomas Hofmann (2012). "Phosphoric Acid and Phosphates". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3. ISBN 978-3527306732.
- ^ a b Christoffersen, Margaret R.; Balic-Zunic, Tonci; Pehrson, Søren; Christoffersen, Jørgen (2000). "Growth and precipitation of a monoclinic calcium pyrophosphate tetrahydrate indicating auto-inhibition at pH7". Journal of Crystal Growth. 212 (3–4): 500–506. Bibcode:2000JCrGr.212..500C. doi:10.1016/S0022-0248(00)00231-1.
- ^ Mandel, Gretchen S.; Renne, Kathleen M.; Kolbach, Ann M.; Kaplan, Wayne D.; Miller, Jay D.; Mandel, Neil S. (1988). "Calcium pyrophosphate crystal deposition disease: Preparation and characterization of crystals". Journal of Crystal Growth. 87 (4): 453–462. Bibcode:1988JCrGr..87..453M. doi:10.1016/0022-0248(88)90093-0.
- ^ Parodi, J. A.; Hickok, R. L.; Segelken, W. G.; Cooper, J. R. (1965). "Electronic Paramagnetic Resonance Study of the Thermal Decomposition of Dibasic Calcium Orthophosphate". Journal of the Electrochemical Society. 112 (7): 688. Bibcode:1965JElS..112..688P. doi:10.1149/1.2423665.
- ^ Hill, W L; Reynolds, D S; Hendbicks, S B; Jacob, K D (1945-02-01). "Nutritive Evaluation of Defluorinated Phosphates and Other Phosphorus Supplements. I. Preparation and Properties of the Samples". Journal of AOAC International. 28 (1): 105–118. doi:10.1093/jaoac/28.1.105. ISSN 0095-9111.
- ^ Calvo, C. (1968-07-01). "Crystal structure of .alpha.-calcium pyrophosphate". Inorganic Chemistry. 7 (7): 1345–1351. doi:10.1021/ic50065a019. ISSN 0020-1669.
- ^ Parodi, J. A.; Hickok, R. L.; Segelken, W. G.; Cooper, J. R. (1965). "Electronic Paramagnetic Resonance Study of the Thermal Decomposition of Dibasic Calcium Orthophosphate". Journal of the Electrochemical Society. 112 (7): 688. Bibcode:1965JElS..112..688P. doi:10.1149/1.2423665.
- ^ Webb, N. C. (1966). "The crystal structure of
β -Ca2P2O". Acta Crystallographica. 21 (6): 942–948. doi:10.1107/S0365110X66004225.