Hypophosphoric Acid

Hypophosphoric Acid 

(H₄P₂O₆), a tetrabasic acid of medium strength. Anhydrous hypophosphoric acid occurs as colorless crystals, which melt at 70°C with decomposition; the crystal hydrates H₄P₂O₆·H₂O and H₄P₂O₆·2H₂O have a melting point of 62°–62.5°C and 79.5°–81.5°C, respectively. The dissociation constants of hypophosphoric acid at 25°C are K₁ = 6 × 10^–3, K₂ = 1.5 × 10^–3, K₃ = 5.4 × 10^–8, and K₄ = 9.3 × 10^–11. When heated, hypophosphoric acid is converted into phosphoric acid (H₃PO₄) and phosphorous acid (H₃PO₃). At temperatures above 180°C it decomposes with the release of phosphine (PH₃). The anhydride of hypophosphoric acid is not known. Salts of hypophosphoric acid are called hypophosphates.

Hypophosphoric acid is formed by the slow oxidation of H₃PO₃ in air or by the oxidation of solid phosphorus in a limited quantity of air (the phosphorus is partially immersed in water). The process is faster under the effect of a calcium hypochlorite mixture on red phosphorus.

REFERENCES

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