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 (JSmol)	Interactive image;
PubChem CID	22222816;
	InChI InChI=1/Cr.5O/q;;;-2;2-1/rCrO4.O/c2-1(3,4)5;/q2-2 Key: ZWPVWTIRZYDPKW-NIUFNKCUAY;
	SMILES O0O[Cr]01(=O)OO1;
Properties
Chemical formula	CrO5
Molar mass	131.991 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).
	(what is ?)
	Infobox references

Chromium(VI) peroxide or chromium oxide peroxide is an unstable compound with the formula CrO₅. 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) 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) peroxide is formed. Chromate or dichromate reacts with hydrogen peroxide and an acid to give chromium peroxide and water.

CrO₄²⁻ + 2 H₂O₂ + 2 H⁺ → CrO₅ + 3 H₂O

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

2 CrO₅ + 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, 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 it is newly formed) is dissolved in the immiscible organic solvent. In this condition, it can be observed over a much longer period.

CrO₅ 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, CrO₅ 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 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[]

^ 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."
^ 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.
^ Stomberg, Rolf (1962). "Crystal Structure of Peroxochromates, CrO₅⋅C₅H₅N". Nature. 196 (4854): 570–571. doi:10.1038/196570b0. S2CID 4187294.

External links[]

Experimental details and photo (in German)
Losing fingers to chemistry on YouTube (8 November 2012). Professor Martyn Poliakoff of the University of Nottingham demonstrates the synthesis on Periodic Videos.

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[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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