Pyrophosphoric Acid

Title: Pyrophosphoric Acid
CAS Registry Number: 2466-09-3
CAS Name: Diphosphoric acid
Molecular Formula: H4O7P2
Molecular Weight: 177.98
Percent Composition: H 2.27%, O 62.93%, P 34.81%
Literature 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).
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.
Melting point: mp 61°
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