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Chromium trioxide

Chromium trioxide
Ball-and-stick model of chromium trioxide
Powder of chromium trioxide
Names
IUPAC name
Chromium trioxide
Other names
Chromic anhydride, Chromium(VI) oxide, Chromic acid (misnomer)
Identifiers
1333-82-0 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:48240 YesY
ChemSpider 14212 YesY
ECHA InfoCard 100.014.189
PubChem 14915
RTECS number GB6650000
UNII 8LV49809UC YesY
UN number 1463
Properties
CrO3
Molar mass 99.99 g·mol−1
Appearance Dark red granular solid, deliquescent
Odor Odorless
Density 2.7 g/cm3 (20 °C)
Melting point 197 °C (387 °F; 470 K)
Boiling point 250 °C (482 °F; 523 K)
decomposes
164.8 g/100 mL (0 °C)
169 g/100 mL (25 °C)
172.6 g/100 mL (40 °C)
198.1 g/100 mL (100 °C)
Solubility Soluble in H2SO4, HNO3, (C2H5)2O, CH3COOH, acetone
+40·10−6 cm3/mol
Thermochemistry
73.2 J/mol·K
−589.3 kJ/mol
Hazards
Safety data sheet ICSC 1194
GHS pictograms The flame-over-circle pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H271, H301, H311, H314, H317, H330, H334, H340, H350, H361, H372, H410
P201, P220, P260, P273, P280, P284
Oxidizing Agent O Very Toxic T+ Dangerous for the Environment (Nature) N
Carc. Cat. 1
Muta. Cat. 2
Repr. Cat. 3
R-phrases R45, R46, R9, R24/25, R26, R35, R42/43, R48/23, R50/53, R62
S-phrases S53, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond
Lethal dose or concentration (LD, LC):
LD50 (median dose)
 80 mg/kg (rats, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY  (what is YesYN ?)
Infobox references

Chromium trioxide is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid under anhydrous conditions, bright orange when wet and which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating. Chromium trioxide is a powerful oxidiser and a suspected carcinogen.

Chromium trioxide is generated by treating sodium chromate or the corresponding sodium dichromate with sulfuric acid:

Approximately 100M kg are produced annually by this or similar routes.

The solid consists of chains of tetrahedrally coordinated chromium atoms that share vertices. Each chromium center, therefore, shares two oxygen centers with neighbors. Two oxygen atoms are not shared, giving an overall stoichiometry of 1:3.

The structure of monomeric CrO3 has been calculated using density functional theory, and is predicted to be pyramidal (point group C3v) rather than planar (point group D3h).

Chromium trioxide decomposes above 197 °C liberating oxygen eventually giving Cr2O3:

It is used in organic synthesis as an oxidant, often as a solution in acetic acid, or acetone in the case of the Jones oxidation. In these oxidations, the Cr(VI) converts primary alcohols to the corresponding carboxylic acids and secondary alcohols to ketones. The reactions are given below:


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