Pyrophosphoric acid

Pyrophosphoric acid

Chemical structure of pyrophosphoric acid
Names
IUPAC names Diphosphoric acid μ-oxido-bis(dihydroxidooxidophosphorus)
Other names Diphosphoric acid
Identifiers
CAS Number	2466-09-3 Y
ChEBI	CHEBI:29888 Y
ChEMBL	ChEMBL1160571 Y
ChemSpider	996 Y
IUPHAR/BPS	3151
Jmol 3D model	Interactive image
PubChem	1023
UNII	4E862E7GRQ Y
InChI InChI=1S/H4O7P2/c1-8(2,3)7-9(4,5)6/h(H2,1,2,3)(H2,4,5,6) Y Key: XPPKVPWEQAFLFU-UHFFFAOYSA-N Y InChI=1/H4O7P2/c1-8(2,3)7-9(4,5)6/h(H2,1,2,3)(H2,4,5,6) Key: XPPKVPWEQAFLFU-UHFFFAOYAX
SMILES O=P(O)(O)OP(=O)(O)O
Properties
Chemical formula	H4P2O7
Molar mass	177.98 g/mol
Melting point	71.5 °C (160.7 °F; 344.6 K)
Solubility in water	Extremely soluble
Solubility	Very soluble in alcohol, ether
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

Pyrophosphoric acid, also known under the name diphosphoric acid, is colorless, odorless, hygroscopic and is soluble in water, diethyl ether, and ethyl alcohol. The anhydrous acid has two different forms, which melt at 54.3°C and 71.5°C. It is best prepared by ion exchange from sodium pyrophosphate or by reacting hydrogen sulfide with lead pyrophosphate. When phosphoric acid is dehydrated pyrophosphoric acid is produced as one of the products. When molten pyrophosphoric acid rapidly forms an equilibrium mixture of phosphoric acid, pyrophosphoric acid and polyphosphoric acids. The percentage by weight of pyrophosphoric acid is around 40% and it is difficult to recrystallise from the melt. In aqueous solution pyrophosphoric acid like all polyphosphoric acids hydrolyses and eventually an equilibrium is established between phosphoric acid pyrophosphoric acid and polyphosphoric acids. When highly diluted an aqueous solution of pyrophosphoric acid contains only phosphoric acid.

H₄P₂O₇ + H₂O ⇌ 2H₃PO₄

Pyrophosphoric acid is a medium strong inorganic acid. Anions, salts, and esters of pyrophosphoric acid are called pyrophosphates.

While pyrophosporic acid is corrosive, it is not known to be otherwise toxic.

History

The name pyrophosphoric acid was given by a "Mr. Clarke of Glasgow" in 1827 who is credited with its discovery following the heating to red heat of a sodium phosphate salt. It was found that phosphoric acid when heated to red heat formed pyrophosphoric acid that was readily converted to phosphoric acid by hot water.

See also

• Sodium pyrophosphate
• Calcium pyrophosphate dihydrate deposition disease
• Dimethylallyl pyrophosphate
• ADP
• ATP
• Ortho acids
• triphosphoric acid

External links

• Pyrophosphoric acid at PubChem