Chromium(VI) oxide peroxide

Chromium(VI) oxide peroxide

Names
Other names chromium(VI) oxide peroxide, chromium pentoxide
Identifiers
CAS Number	35262-77-2
3D model (Jmol)	Interactive image
InChI InChI=1/Cr.5O/q;;;-2;2*-1/rCrO4.O/c2-1(3,4)5;/q2*-2 Key: ZWPVWTIRZYDPKW-NIUFNKCUAY
SMILES [O-2].[O-][Cr]([O-])(=O)=O
Properties
Chemical formula	CrO5
Molar mass	131.99 g·mol^−1
Solubility in water	soluble (decomposes without stabilisers)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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 metal chromates or dichromates, such as sodium chromate or potassium dichromate. The generally yellow chromates or orange dichromates turn to dark blue as chromium(VI) peroxide is formed. Chromate or dichromate reacts with hydrogen peroxide and an acid to give chromium peroxide and water.

CrO₄^2- + 2 H₂O₂ + 2 H⁺ → CrO₅ + 3 H₂O

After a few seconds, the chromium(VI) peroxide decomposes to turn green as chromium(III) compounds are formed.^[1] To avoid this decomposition, it is possible to stabilize chromium(VI) oxide peroxide in a water-immiscible organic solvent such as diethyl ether, butan-1-ol or amyl acetate by adding a layer of the organic solvent above the chromate/dichromate solution and shaking during the addition of hydrogen peroxide. In this way, the chromium(VI) peroxide (unstable in the aqueous phase in which newly formed) is dissolved in the immiscible organic solvent. 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

The etherate, bipyridyl and pyridyl complexes of this compound 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)