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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.
The etherate, bipyridyl and pyridyl complexes of this compound have been found to be effective oxidants in organic chemistry. The structure of the pyridyl complex has been determined crystallographically.
File:Solution of CrO5.jpg, An aqueous solution of chromium peroxide
File:CrO5.jpg, A very dilute solution of chromium peroxide
File:Chromium(VI) oxide peroxide (stabilized in ether phase).jpg, chromium(VI) oxide peroxide stabilized in ether phase (above) and chromium(III) aqueous solution (below).
Experimental details and photo
* (8 November 2012). Professor
Preparation and properties
Chromium(VI) peroxide is formed by the addition of acidifiedhydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%â ...
solutions to solutions of metal chromates or dichromates, such as sodium chromate
Sodium chromate is the inorganic compound with the formula Na2CrO4. It exists as a yellow hygroscopic solid, which can form tetra-, hexa-, and decahydrates. It is an intermediate in the extraction of chromium from its ores.
Production and react ...
or potassium dichromate
Potassium dichromate, , is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health ...
. 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.
: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
Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...
, butan-1-ol
1-Butanol, also known as butan-1-ol or ''n''-butanol, is a primary alcohol with the chemical formula C4H9OH and a linear structure. Isomers of 1-butanol are isobutanol, butan-2-ol and ''tert''-butanol. The unmodified term butanol usually refer ...
or amyl acetate
Amyl acetate (pentyl acetate) is an organic compound and an ester with the chemical formula CH3COO H2sub>4CH3 and the molecular weight 130.19g/mol. It is colorless and has a scent similar to bananas and apples. The compound is the condensation p ...
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 aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
s 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
The etherate, bipyridyl and pyridyl complexes of this compound have been found to be effective oxidants in organic chemistry. The structure of the pyridyl complex has been determined crystallographically.
Gallery
See also
*Tetraperoxochromate
Potassium peroxochromate, potassium tetraperoxochromate(V), or simply potassium perchromate, is an inorganic chemical having the chemical formula K3 r(O2)4 It is a red-brown paramagnetic solid. It is the potassium salt of tetraperoxochromate(V), ...
- an similarly-synthesized analogous chromium(V) peroxide complex
References
External links
Experimental details and photo
* (8 November 2012). Professor
Martyn Poliakoff
Sir Martyn Poliakoff (born 16 December 1947) is a British chemist, working on gaining insights into fundamental chemistry, and on developing environmentally acceptable processes and materials. The core themes of his work are supercritical fluid ...
of the University of Nottingham
, mottoeng = A city is built on wisdom
, established = 1798 – teacher training college1881 – University College Nottingham1948 – university status
, type = Public
, chancellor ...
demonstrates the synthesis on ''Periodic Videos
''Periodic Videos'' (also known as ''The Periodic Table of Videos'') is a video project and YouTube channel on chemistry. It consists of a series of videos about chemical elements and the periodic table, with additional videos on other topics i ...
''.
Peroxides
Chromates
Transition metal oxides
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