7355. Phosphorus Pentoxide

Nomenclature

CAS number: 1314-56-3
Phosphorous oxide (P2O5); phosphoric anhydride; diphosphorus pentoxide.
O5P2; mol wt 141.94.
O 56.36%, P 43.64%.
P2O5.

Description and references

Exists as P4O10. Prepd commercially by burning phosphorus in a current of dry air. Purification: Manley, J. Chem. Soc. 121, 331 (1922); de Decker, McGillavry, Rec. Trav. Chim. 60, 153, 413 (1941). Review of phosphorus oxides: J. R. Van Waser, Phosphorus and Its Compounds vol. 1 (Interscience, New York, 1958) pp 267-286.

Properties

Very deliquescent crystals. Corrosive. Several crystalline and amorphous modifications. Commercial form; hexagonal; d 2.30. mp 340°. Sublimation temperature 360°. Nonflammable. Does not support combustion. Heat of formation: -365.83 kcal/mole. Sp heat: 0.170 cal/g/°C. Heat of fusion: 8.2 kcal/mole. Heat of volatilization: 22.7 kcal/mole of P4O10. Readily absorbs moisture from the air. Exothermic hydrolysis by water to form phosphoric acid. The reaction with alcohol is similar.

Caution

Strong irritant; corrosive to skin, mucous membranes and eyes.

Use

Drying and dehydrating agent. Condensing agent in organic synthesis.