Calcium pyrophosphate

Calcium pyrophosphate
Names
	IUPAC name Calcium diphosphate
	Other names Diphosphoric acid, calcium salt (1:2); Dicalcium diphosphate; Dicalcium pyrophosphate;
Identifiers
CAS Number	7790-76-3 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:32598 ;
ChemSpider	23034 ;
ECHA InfoCard	100.029.292
E number	E450(vi) (thickeners, ...)
MeSH	Calcium+pyrophosphate
PubChem CID	24632;
UNII	X69NU20D19 ;
CompTox Dashboard (EPA)	DTXSID50872512 ;
	InChI InChI=1S/2Ca.H4O7P2/c;;1-8(2,3)7-9(4,5)6/h;;(H2,1,2,3)(H2,4,5,6)/q2+2;/p-4 Key: JUNWLZAGQLJVLR-UHFFFAOYSA-J ; InChI=1/2Ca.H4O7P2/c;;1-8(2,3)7-9(4,5)6/h;;(H2,1,2,3)(H2,4,5,6)/q2+2;/p-4 Key: JUNWLZAGQLJVLR-XBHQNQODAN;
	SMILES [Ca+2].[Ca+2].[O-]P([O-])(=O)OP([O-])([O-])=O;
Properties
Chemical formula	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)
Solubility in water	insoluble
Solubility	soluble in HCl, nitric acids
Refractive index (nD)	1.585
Hazards
NFPA 704 (fire diamond)	2 0 0
Flash point	Non-flammable
Related compounds
Other anions	Calcium phosphate
Other cations	Magnesium pyrophosphate; Sodium pyrophosphate
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Calcium pyrophosphate refers to any member of a series of inorganic compound with the formula Ca₂P₂O₇(H₂O)_n. They are white solids that are insoluble in water. They contain the pyrophosphate anion, although sometimes they are referred to as phosphates. The inventory includes 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. Ca₂P₂O₇ is commonly used as a mild abrasive agent in toothpastes because of its insolubility and nonreactivity toward fluoride.