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 Y

3D model (JSmol)

* Interactive image

ChEBI |

* CHEBI:32598 Y

ChemSpider |

* 23034 Y

MeSH | Calcium+pyrophosphate

PubChem CID

* 24632

UNII |

* X69NU20D19 Y

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 Y

Key: JUNWLZAGQLJVLR-UHFFFAOYSA-J Y

* 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)  |

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).

Y verify (what is YN ?)
Infobox references

Calcium pyrophosphate refers to any member of a series of inorganic compound with the formula Ca

7(H
2O)
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 is 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 because of its insolubility and nonreactivity toward fluoride.[2]

## Preparation

Crystals of the tetrahydrate can be prepared by treating a solution of sodium pyrophosphate with calcium nitrate with careful control of 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:[2]

2 CaHPO4 → Ca2P2O7 \+ H2O

At 240-500 °C an amorphous phase is formed, heating to 750 °C forms β-Ca2P2O7, heating to 1140 - 1350 °C forms the α-Ca2P2O7.

## Structure of anhydrous and hydrated forms

The 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 three polymorphs: α-, β-, and metastable γ[5] (Tα/β=1140ºС[6]). The high temperature form α- is monoclinic (P21/n, a=12.66(1)Å, b=8.542(8)Å, c=5.315(5)Å, Z=4, ρα=2.95 g/cm3), with 8 coordinate calcium, the lower temperature form β- is tetragonal (P41, a=b=6.684Å, c=24.144Å, V=915.40Å3, Z=8, ρβ=3.128 g/cm3), with calcium in four different coordination environments, two that are 7 coordinate, one 8 and one 9. In both the pyrophosphates are essentially eclipsed.[7][8][9]

## References

1. ↑ Calcium Pyrophosphate Deposition Disease at eMedicine
2. ↑ 2.0 2.1 Klaus Schrödter; Gerhard Bettermann; Thomas Staffel; Friedrich Wahl; Thomas Klein; Thomas Hofmann (2012). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3.
3. ↑ 3.0 3.1 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. doi:10.1016/S0022-0248(00)00231-1. Bibcode: 2000JCrGr.212..500C.
4. ↑ 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. doi:10.1016/0022-0248(88)90093-0. Bibcode: 1988JCrGr..87..453M.
5. ↑ 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" (in en). Journal of the Electrochemical Society 112 (7): 688. doi:10.1149/1.2423665. Bibcode: 1965JElS..112..688P. https://iopscience.iop.org/article/10.1149/1.2423665.
6. ↑ 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. https://doi.org/10.1093/jaoac/28.1.105.
7. ↑ Calvo, C. (1968-07-01). "Crystal structure of .alpha.-calcium pyrophosphate". Inorganic Chemistry 7 (7): 1345–1351. doi:10.1021/ic50065a019. ISSN 0020-1669. https://doi.org/10.1021/ic50065a019.
8. ↑ 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. doi:10.1149/1.2423665. Bibcode: 1965JElS..112..688P.
9. ↑ Webb, N. C. (1966). "The crystal structure of β-Ca2P2O". Acta Crystallographica 21 (6): 942–948. doi:10.1107/S0365110X66004225.

* v
* t
* e

Calcium compounds

* CaAl2O4
* CaB6
* CaBr2
* Ca(BrO3)2
* CaC2
* CaCN2
* Ca(CN)2
* CaCO3
* CaC2O4
* CaCl2
* Ca(ClO)2
* Ca(ClO3)2
* CaCrO4
* CaF2
* CaH2
* Ca(HCO3)2
* CaH2S2O6
* CaI2
* Ca(IO3)2
* Ca(MnO4)2
* CaN6
* Ca(NO3)2
* CaO
* CaO2
* Ca(OH)2
* CaP
* CaS
* CaSO3
* CaSO4
* CaSe
* CaSi
* CaSi2
* CaTiO3
* Ca2P2O7
* Ca2SiO4
* Ca3Al2O6
* Ca3(AsO4)2
* Ca3(BO3)2
* Ca3(C6H5O7)2
* Ca3N2
* Ca3P2
* Ca4(PO4)2O
* Ca3(PO4)2
* Ca(H2PO4)2
* CaHPO4
* C36H70CaO4

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