Peroxydiphosphoric acid

Peroxydiphosphoric acid
Names
	Other names peroxodiphosphoric acid
Identifiers
CAS Number	potassium salt: 15593-49-4;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:29284;
ChemSpider	103142;
PubChem CID	115278;
	InChI InChI=1S/H4O8P2/c1-9(2,3)7-8-10(4,5)6/h(H2,1,2,3)(H2,4,5,6) Key: NUGJFLYPGQISPX-UHFFFAOYSA-N; InChI=1S/H4O8P2/c1-9(2,3)7-8-10(4,5)6/h(H2,1,2,3)(H2,4,5,6);
	SMILES OP(=O)(O)OOP(=O)(O)O;
Properties
Chemical formula	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). Infobox references

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.

History[edit]

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.

{\ce {H4P2O7 + H2O2 -> H4P2O8 + H2O}}

Preparation[edit]

Peroxydiphosphoric acid can be prepared by the reaction between phosphoric acid and fluorine, with peroxymonophosphoric acid being a by-product.^[2]

{\ce {2H3PO4 + F2 -> H4P2O8 + 2HF}}

The compound is not commercially available and must be prepared as needed.^[2] Peroxodiphosphates can be obtained by electrolysis of phosphate solutions.^[3]

Properties[edit]

Peroxydiphosphoric acid is a tetraprotic acid, with acid dissociation constants given by pK_a1 ≈ −0.3, pK_a2 ≈ 0.5, pK_a3 = 5.2 and pK_a4 = 7.6.^[4] In aqueous solution, it disproportionates upon heating to peroxymonophosphoric acid and phosphoric acid.^[5]

{\ce {H4P2O8 + H2O <=> H3PO5 + H3PO4}}

References[edit]

^ Schmidlin, Julius; Massini, Paul (1910). "Phosphormonopersäure und Überphosphorsäure". Ber. Dtsch. Chem. Ges. 43 (1): 1162–1171. doi:10.1002/cber.191004301195.
^ ^a ^b Harald, Jakob; Leininger, Stefan; Lehmann, Thomas; Jacobi, Sylvia; Gutewort, Sven (2007). "Peroxo Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Wiley‐VCH Verlag. pp. 310–311. doi:10.1002/14356007.a19_177.pub2. ISBN 9783527306732.
^ Riedel, Erwin (2004). Anorganische Chemie (6 ed.). Berlin/New York: de Gruyter. p. 493.
^ Crutchfield, Marvin M.; Edwards, John O. (1960). "The Acidity and Complexes of Peroxydiphosphoric Acid". J. Am. Chem. Soc. 82 (14): 3533–3537. doi:10.1021/ja01499a015.
^ Kolditz, Lothar (1983). Anorganische Chemie. Vol. 1. Berlin: Deutscher Verlag der Wissenschaften. p. 437.

[1] Schmidlin, Julius; Massini, Paul (1910). "Phosphormonopersäure und Überphosphorsäure". Ber. Dtsch. Chem. Ges. 43 (1): 1162–1171. doi:10.1002/cber.191004301195.

[:1-2] Harald, Jakob; Leininger, Stefan; Lehmann, Thomas; Jacobi, Sylvia; Gutewort, Sven (2007). "Peroxo Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Wiley‐VCH Verlag. pp. 310–311. doi:10.1002/14356007.a19_177.pub2. ISBN 9783527306732.

[Riedel2-3] Riedel, Erwin (2004). Anorganische Chemie (6 ed.). Berlin/New York: de Gruyter. p. 493.

[Edwards"-4] Crutchfield, Marvin M.; Edwards, John O. (1960). "The Acidity and Complexes of Peroxydiphosphoric Acid". J. Am. Chem. Soc. 82 (14): 3533–3537. doi:10.1021/ja01499a015.

[Kolditz2-5] Kolditz, Lothar (1983). Anorganische Chemie. Vol. 1. Berlin: Deutscher Verlag der Wissenschaften. p. 437.

[1]

[2]

[3]

[4]

[5]