Chromium trioxide

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Chromium trioxide
Ball-and-stick model of chromium trioxide
Powder of chromium trioxide
Identifiers
CAS number 1333-82-0 YesY
PubChem 14915
ChemSpider 14212 YesY
UNII 8LV49809UC YesY
UN number 1463
ChEBI CHEBI:48240 YesY
RTECS number GB6650000
Jmol-3D images Image 1
Properties
Molecular formula CrO3
Molar mass 99.99 g mol−1
Appearance Dark red granular solid, deliquescent
Odor Odorless
Density 2.7 g/cm3 (20 °C)[1]
Melting point 197 °C (387 °F; 470 K) [1]
Boiling point 250 °C (482 °F; 523 K)
decomposes[1]
Solubility in water 164.8 g/100 mL (0 °C)
169 g/100 mL (25 °C)[1]
172.6 g/100 mL (40 °C)
198.1 g/100 mL (100 °C)[2]
Solubility Soluble in H2SO4, HNO3, (C2H5)2O, CH3COOH, acetone
Magnetic susceptibility 4·10−5 cm3/mol[1]
Thermochemistry
Std molar
entropy
So298
73.2 J/mol·K[3]
Std enthalpy of
formation
ΔfHo298
−589.3 kJ/mol[4]
Hazards
MSDS 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)[5]
GHS signal word Danger
GHS hazard statements H271, H301, H311, H314, H317, H330, H334, H340, H350, H361, H372, H410[5]
GHS precautionary statements P201, P220, P260, P273, P280, P284[5]
EU Index 024-001-00-0
EU classification 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
LD50 80 mg/kg (rats, oral)[6]
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Chromium trioxide is the inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.[6] 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.[7]

Production, structure, and basic reactions[edit]

Chromium trioxide is generated by treating sodium chromate or the corresponding sodium dichromate with sulfuric acid:[6]

H2SO4 + Na2Cr2O7 → 2 CrO3 + Na2SO4 + H2O

Approximately 100M kg are produced annually by this or similar routes.[7]

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.[8][9]

Ball-and-stick model of chains in the crystal structure of CrO3

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).[10]

Ball-and-stick model of the DFT-calculated structure of the CrO3 monomer

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

4 CrO3 → 2 Cr2O3 + 3 O2

It is used in organic synthesis as an oxidant, often as a solution in acetic acid,[8] 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:

  • Primary alcohols
4 CrO3 + 3 RCH2OH + 12 H+ → 3 RCOOH + 4 Cr3+ + 9 H2O
  • Secondary alcohols
2 CrO3 + 3 R2CHOH + 6 H+ → 3 R2C=O + 2 Cr3+ + 6 H2O

Applications[edit]

Chromium trioxide is mainly used in chrome plating. It is typically employed with additives that affect the plating process but do not react with the trioxide. The trioxide reacts with cadmium, zinc, and other metals to generate passivating chromate films that resist corrosion. It is also used in the production of synthetic rubies. Chromic acid solution is also used in applying types of anodic coating to aluminium, which are primarily used in aerospace applications. A Chromic Acid/ Phosphoric Acid solution is also the preferred stripping agent of anodic coatings of all types.

Safety[edit]

Chromium trioxide igniting ethanol

Chromium trioxide is highly toxic, corrosive, and carcinogenic.[11] It is the main example of hexavalent chromium, an environmental hazard. The related chromium(III) derivatives are not particularly dangerous; thus, reductants are used to destroy chromium(VI) samples.

Chromium trioxide, being a powerful oxidizer, will ignite some organic materials (such as ethanol) on contact.

References[edit]

  1. ^ a b c d e Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0. 
  2. ^ Seidell, Atherton; Linke, William F. (1919). Solubilities of Inorganic and Organic Compounds (2nd ed.). D. Van Nostrand Company. p. 250. 
  3. ^ http://chemister.ru/Database/properties-en.php?dbid=1&id=3425
  4. ^ Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. The McGraw-Hill Companies, Inc. ISBN 0-07-049439-8. 
  5. ^ a b c Sigma-Aldrich Co., Chromium(VI) oxide. Retrieved on 2014-06-15.
  6. ^ a b c d "CHROMIUM TRIOXIDE". http://www.chemicalland21.com. AroKor Holdings Inc. Retrieved 2014-06-15. 
  7. ^ a b Anger, G.; Halstenberg, J.; Hochgeschwender, K.; Scherhag, C.; Korallus, U.; Knopf, H.; Schmidt, P.; Ohlinger, M. (2000). "Chromium Compounds". "Ullmann's Encyclopedia of Industrial Chemistry". doi:10.1002/14356007.a07_067. ISBN 3527306730.  edit
  8. ^ a b Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5 
  9. ^ Stephens, J. S.; Cruickshank, D. W. J. (1970). "The crystal structure of (CrO3)∞". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry 26 (3): 222. doi:10.1107/S0567740870002182.  edit
  10. ^ Zhai, H. J.; Li, S.; Dixon, D. A.; Wang, L. S. (2008). "Probing the Electronic and Structural Properties of Chromium Oxide Clusters (CrO3)n−and (CrO3)n(n= 1–5): Photoelectron Spectroscopy and Density Functional Calculations". Journal of the American Chemical Society 130 (15): 5167. doi:10.1021/ja077984d.  edit
  11. ^ "Chromium Trioxide (MSDS)". J. T. Baker. Retrieved 2007-09-13. 

External links[edit]