Peroxodiphosphoric acid

Structural formula
General
Surname	Peroxodiphosphoric acid
other names	Peroxydiphosphoric acid Over phosphoric acid
Molecular formula	H 4 P 2 O 8
External identifiers / databases
CAS number 13825-81-5 Wikidata Q21099515
properties
Molar mass	193.97 mol −1
safety instructions
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Peroxodiphosphoric acid is an oxo acid of phosphorus . Their salts are called peroxodiphosphates . Along with peroxomonophosphoric acid, it is one of the two known peroxophosphoric acids.

history

The two peroxophosphoric acids were first produced and described by Julius Schmidlin and Paul Massini in 1910. Here it was obtained in poor yield from highly concentrated diphosphoric acid and hydrogen peroxide .

${\displaystyle \mathrm {H_{4}P_{2}O_{7}+H_{2}O_{2}\rightarrow H_{4}P_{2}O_{8}+H_{2}O} }$

Extraction and presentation

Peroxodiphosphoric acid can be obtained by reacting phosphoric acid with fluorine , with peroxomonophosphoric acid also being formed as a by-product.

${\displaystyle \mathrm {2\,H_{3}PO_{4}+F_{2}\rightarrow H_{4}P_{2}O_{8}+2\,HF} }$

The connection is not commercially available and must be established prior to use. Peroxodiphosphates are obtained by anodic oxidation of phosphate solutions .

properties

Peroxodiphosphoric acid is a tetrabasic acid. The four acid constants are pK _S1 ≈ −0.3, pK _S2 ≈ 0.5, pK _S3 = 5.2 and pK _S4 = 7.6. In aqueous solution, disproportionation to peroxomonophosphoric acid and phosphoric acid takes place on heating .

${\displaystyle \mathrm {H_{4}P_{2}O_{8}+H_{2}O\rightleftharpoons H_{3}PO_{5}+H_{3}PO_{4}} }$

Individual evidence

1. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
2. ↑ Entry on peroxophosphates. In: Römpp Online . Georg Thieme Verlag, accessed on September 11, 2015.
3. ↑ Julius Schmidlin, Paul Massini: Phosphormonopersäure und überphosphorsäure. In: Reports of the German Chemical Society . 43, No. 1, 1910, pp. 1162-1171, doi : 10.1002 / cber.191004301195 .
4. ↑ ^{a b} Harald Jakob, Stefan Leininger, Thomas Lehmann, Sylvia Jacobi, Sven Gutewort: Peroxo Compounds, Inorganic. In: Ullmann's Encyclopedia of Industrial Chemistry . Wiley-VCH, 2000, ISBN 978-3-527-30673-2 , doi : 10.1002 / 14356007.a19_177.pub2 .
5. ↑ Erwin Riedel : Inorganic Chemistry . 6th edition, de Gruyter, Berlin / New York 2004, p. 493.
6. ^ Marvin M. Crutchfield, John O. Edwards: The Acidity and Complexes of Peroxydiphosphoric Acid. In: Journal of the American Chemical Society . 82, No. 14, 1960, pp. 3533-3537, doi : 10.1021 / ja01499a015 .
7. ↑ Lothar Kolditz : Inorganic Chemistry . Volume 1, Deutscher Verlag der Wissenschaften, Berlin 1983, p. 437.