Chemistry:Pyrophosphoric acid

From HandWiki
Pyrophosphoric acid
Chemical structure of pyrophosphoric acid
3D model of pyrophosphoric acid
Names
IUPAC names
Diphosphoric acid
μ-oxido-bis(dihydroxidooxidophosphorus)
Other names
Diphosphoric acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
UNII
Properties
H4P2O7
Molar mass 177.97 g/mol
Melting point 71.5 °C (160.7 °F; 344.6 K)
Extremely soluble
Solubility Very soluble in alcohol, ether
Conjugate base 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 ☑Y☒N ?)
Infobox references

Pyrophosphoric acid, also known as diphosphoric acid, is the inorganic compound with the formula H4P2O7 or, more descriptively, [(HO)2P(O)]2O. Colorless and odorless, it is soluble in water, diethyl ether, and ethyl alcohol. The anhydrous acid crystallizes in two polymorphs, which melt at 54.3 °C and 71.5 °C. The compound is not particularly useful, except that it is a component of polyphosphoric acid and the conjugate acid of the pyrophosphate anion. Anions, salts, and esters of pyrophosphoric acid are called pyrophosphates.

Preparation

It is best prepared by ion exchange from sodium pyrophosphate or by treating lead pyrophosphate with hydrogen sulfide. It is not prepared by dehydration of phosphoric acid. Instead, pyrophosphoric acid is produced as only one of the products.

Reactions

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.[1]

H4P2O7 + H2O ⇌ 2H3PO4

Pyrophosphoric acid is a medium strong inorganic acid.

Safety

While pyrophosporic acid is corrosive, it is not known to be otherwise toxic.[2]

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.[3]

See also

References

External links