Chromium(VI) oxide peroxide
Names
IUPAC name
Chromium(VI) oxide diperoxide
Other names
  • Chromium(VI) oxide peroxide
  • Chromium pentoxide
Identifiers
3D model (JSmol)
  • InChI=1/Cr.5O/q;;;-2;2*-1/rCrO4.O/c2-1(3,4)5;/q2*-2
    Key: ZWPVWTIRZYDPKW-NIUFNKCUAY
  • O0O[Cr]01(=O)OO1
Properties
CrO(O2)2
Molar mass 131.991 g·mol−1
Appearance Dark blue
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) oxide peroxide or chromium oxide peroxide or more accurately chromium(VI) oxide diperoxide is an inorganic compound with the chemical formula CrO5 or more accurately CrO(O2)2. It is an unstable dark blue compound. This compound contains one oxo ligand and two peroxo ligands, making a total of five oxygen atoms per chromium atom.

Preparation and properties

Chromium(VI) oxide peroxide is 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) oxide peroxide is formed. Chromate or dichromate reacts with hydrogen peroxide and an acid to give chromium peroxide and water.

CrO2−4 + 2 H2O2 + 2 H+ → CrO(O2)2 + 3 H2O

With this method, the chromium(VI) oxide peroxide will decompose after a few seconds, turning green as chromium(III) compounds are formed.[1]

2 CrO(O2)2 + 7 H2O2 + 6 H+ → 2 Cr3+ + 10 H2O + 7 O2

To avoid this decomposition, it is possible to stabilize chromium(VI) oxide peroxide in water-immiscible organic solvents such as diethyl ether, 1-butanol, ethyl acetate 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) oxide peroxide (unstable in the aqueous phase in which it is newly formed) is dissolved in the immiscible organic solvent. In this condition, it can be observed over a much longer period.

CrO(O2)2 is unstable and decomposes on standing to form CrO3. It is incompatible with ketones and primary alcohols, as it oxidizes them to aldehydes and carboxylic acids while being itself reduced to Cr3+. Therefore, CrO(O2)2 is a good oxidizing agent, even better than chromates and dichromates due to the presence of two reactive peroxo ligands, but due to its low stability it is not used in organic syntheses.

Derivatives

Structure of the complex of CrO(O2)2 with pyridine (The hydrogen atoms bonded to carbon atoms are missing.)
  Vanadium, V
  Carbon, C
  Hydrogen, H
  Oxygen, O
  Nitrogen, N

The etherate, bis(pyridine) and pyridine complexes of this compound have been found to be effective oxidants in organic chemistry.[2]

The structure of the pyridine complex has been determined crystallographically.[3]

See also

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): 570–571. doi:10.1038/196570b0. S2CID 4187294.
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