Phosphorus Pentoxide
Title: Phosphorus Pentoxide
CAS Registry Number: 1314-56-3
CAS Name: Phosphorous oxide (P2O5)
Additional Names: phosphoric anhydride; diphosphorus pentoxide
Molecular Formula: O5P2
Molecular Weight: 141.94
Percent Composition: O 56.36%, P 43.64%
Line Formula: P2O5
Literature 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.
Melting point: mp 340°
Density: d 2.30
CAUTION: Strong irritant; corrosive to skin, mucous membranes and eyes.
Use: Drying and dehydrating agent. Condensing agent in organic synthesis.

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