8008. Pyrophosphoric Acid

Nomenclature

CAS number: 2466-09-3
Diphosphoric acid.
H4O7P2; mol wt 177.98.
H 2.27%, O 62.93%, P 34.81%.

Description and references

Prepd according to the equation 5H3PO4 + POCl3 → 3H4P2O7 + 3HCl: Geuther, J. Prakt. Chem. [2] 8, 359 (1874); Partington, Wallsom, Chem. News 136, 97 (1928); by heating H3PO4: Bell, Ind. Eng. Chem. 40, 1464 (1948).

Chemical structure

Properties

Hygroscopic glass, seldom acicular crystals, mp 61°. K1 at 18° = 0.14; K2 = 0.011; K3 = 2.1 × 10-7; K4 = 4.1 × 10-10. Forms normal salts, such as Na4P2O7, and dihydrogen salts, such as Na2H2P2O7. Solubility in water (23°): 709 g/100 ml. Quickly converted to phosphoric acid when dissolved in hot water. Sol in alcohol and ether.