Peroxydiphosphoric acid (H4P2O8) is an oxyacid of phosphorus. Its salts are known as peroxydiphosphates. It is one of two peroxyphosphoric acids, along with peroxymonophosphoric acid.
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Other names
peroxodiphosphoric acid | |
Identifiers | |
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Properties | |
H4P2O8 | |
Molar mass | 193.97 g/mol |
Related compounds | |
Related compounds |
peroxymonophosphoric acid |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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History
Both peroxyphosphoric acids were first synthesized and characterized in 1910 by Julius Schmidlin and Paul Massini,[1] where peroxydiphosphoric acid was obtained in poor yields from the reaction between diphosphoric acid and highly-concentrated hydrogen peroxide.
Preparation
Peroxydiphosphoric acid can be prepared by the reaction between phosphoric acid and fluorine, with peroxymonophosphoric acid being a by-product.[2]
The compound is not commercially available and must be prepared as needed.[2] Peroxodiphosphates can be obtained by electrolysis of phosphate solutions.[3]
Properties
Peroxydiphosphoric acid is a tetraprotic acid, with acid dissociation constants given by pKa1 ≈ −0.3, pKa2 ≈ 0.5, pKa3 = 5.2 and pKa4 = 7.6.[4] In aqueous solution, it disproportionates upon heating to peroxymonophosphoric acid and phosphoric acid.[5]
References
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