Chromium(VI) oxide peroxide

Chromium(VI) oxide peroxide
Other names chromium(VI) oxide peroxide
Identifiers
Jmol-3D images	Image 1
SMILES [O-2].[O-][Cr]([O-])(=O)=O
InChI InChI=1/Cr.5O/q;;;-2;2*-1/rCrO4.O/c2-1(3,4)5;/q2*-2 Key: ZWPVWTIRZYDPKW-NIUFNKCUAY
Properties
Molecular formula	CrO5
Molar mass	131.99 g mol−1
Solubility in water	soluble (decomposes without stabilisers)
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chromium(VI) peroxide (CrO₅) or chromium oxide peroxide is an unstable compound formed by the addition of acidified hydrogen peroxide solutions to solutions of chromates, such as sodium chromate. The generally yellow chromates turn to dark blue-brown as chromium(VI) peroxide is formed. The metal chromate reacts with hydrogen peroxide and an acid to give chromium peroxide, water, and the metal salt of the acid.

M₂CrO₄ + 2 H₂O₂ + 2 H⁺ → CrO₅ + 3 H₂O + 2 M⁺

After a few seconds, they decompose to turn green as chromium(III) compounds are formed.^[1] To avoid this decomposition, it is possible to stabilize chromium(VI) oxide peroxide in diethyl ether by adding a layer of ether above the (bi)chromate solution and shaking during the addition of hydrogen peroxide, so that the chromium(VI) peroxide (unstable in the aqueous phase in which newly formed) is dissolved in ether. In this condition it can be observed over a much longer period.

2 CrO₅ + 7 H₂O₂ + 6 H⁺ → 2 Cr³⁺ + 10 H₂O + 7 O₂

This compound contains one oxo ligand and two peroxo ligands, making a total of five oxygen atoms per chromium atom.

Derivatives

Structure of the complex of CrO₅ with pyridine

This compound as the stabilized etherate, bipyridyl and pyridyl complexes have been found to be effective oxidants in organic chemistry.^[2] The structure of the pyridyl complex has been determined crystallographically.^[3]

Gallery

• 

  An aqueous solution of chromium peroxide

• 

  A very dilute solution of chromium peroxide

• 

  chromium(VI) oxide peroxide stabilized in ether phase (above) and chromium(III) aqueous solution (below).

References

1. ^ Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils; (1985). "Chromium" (in German). Lehrbuch der Anorganischen Chemie (91–100 ed.). Walter de Gruyter. pp. 1081–1095. ISBN 3-11-007511-3."
2. ^ Firouzabadi, H.; Iranpoor, N.; Kiaeezadeh, F.; Toofan, J. (1986). "Chromium(VI) based oxidants-1 Chromium peroxide complexes as versatile, mild, and efficient oxidants in organic synthesis". Tetrahedron 42: 719. doi:10.1016/S0040-4020(01)87476-7. 
3. ^ Stomberg, Rolf (1962). "Crystal Structure of Peroxochromates, CrO₅⋅C₅H₅N". Nature 196 (4854): 570. doi:10.1038/196570b0. 

External links

• Experimental details and photo (German)