Chromium trioxide

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Chromium trioxide
Ball-and-stick model of chromium trioxide CrO3-from-xtal-1970-bulk-3D-balls.png
Ball-and-stick model of chromium trioxide
   Chromium, Cr
   Oxygen, O
Powder of chromium trioxide Chromium(VI) oxide.jpg
Powder of chromium trioxide
Names
IUPAC name
Chromium trioxide
Other names
Chromic anhydride, Chromium(VI) oxide, Chromic acid (misnomer)
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.014.189 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
RTECS number
  • GB6650000
UNII
UN number 1463
  • InChI=1S/Cr.3O Yes check.svgY
    Key: WGLPBDUCMAPZCE-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/Cr.3O/rCrO3/c2-1(3)4
    Key: WGLPBDUCMAPZCE-YFSAMUSXAF
  • O=[Cr](=O)=O
Properties
CrO3
Molar mass 99.993 g·mol−1
AppearanceDark 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]
  • 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, (CH3CH2)2O, CH3COOH, (CH3)2CO
+40·10−6 cm3/mol [1]
Thermochemistry
Std molar
entropy (S⦵298)
73.2 J/(mol·K) [3]
−589.3 kJ/mol [4]
Hazards
GHS labelling:
GHS-pictogram-rondflam.svg GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg [5]
Danger
H271, H301+H311, H314, H317, H330, H334, H335, H340, H350, H361f, H372, H410 [5]
P210, P260, P280, P303+P361+P353, P304+P340+P310, P305+P351+P338 [5]
NFPA 704 (fire diamond)
[6]
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
4
0
2
OX
Lethal dose or concentration (LD, LC):
80 mg/kg (rats, oral) [6]
Safety data sheet (SDS) ICSC 1194
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is the inorganic compound with the formula CrO3. [7] It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. [6]

Contents

This compound is a dark-purple solid. Millions of kilograms are produced annually, mainly for electroplating. [8] Chromium trioxide is a powerful oxidiser, a mutagen, and a carcinogen. [9]

Production and structure

Chromium trioxide is generated by treating sodium dichromate with sulfuric acid: [6]

H2SO4 + Na2Cr2O7 → 2 CrO3 + Na2SO4 + H2O

Approximately 100,000 tonnes are produced annually by this or similar routes. [8]

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. [10] [11]

Ball-and-stick model of chains in the crystal structure of CrO3 Chromium, Cr Oxygen, O CrO3-from-xtal-1970-chain-3D-balls.png
Ball-and-stick model of chains in the crystal structure of CrO3
   Chromium, Cr
   Oxygen, O

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). [12]

CrO3-monomer-from-DFT-PW91-aD-2008-side-3D-balls.png

Reactions

Chromium trioxide decomposes above 197 °C, liberating oxygen and eventually giving Cr2O3: [7]

4 CrO3 → 2 Cr2O3 + 3 O2

With water it converts to "chromic acid", which includes red-orange species such as H2CrO4 and H2Cr2O7. [7]

Chromium trioxide is a Lewis acid, forming adducts with many (non-oxidizable) bases, such as chloride: [13]

CrO3 + Cl− → CrO3Cl−

Applications

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. On the International Space Station, it is used to control bacteria growth in the wastewater storage tank. A chromic acid/phosphoric acid solution is also the preferred stripping agent of anodic coatings of all types.

Organic chemistry

Chromium trioxide and a variety of its derivatives are used in organic chemistry. Some of these reagents:

Typically these reagents convert alcohols to carbonyls: [16]

Safety

Chromium trioxide is highly toxic, corrosive, and carcinogenic. [17] It is the main example of hexavalent chromium, an environmental hazard. [18] 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 organic materials such as alcohols on contact.

Images

References

  1. 1 2 3 4 5 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. ↑ "chromium(VI) oxide". chemister.ru.
  4. ↑ Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. The McGraw-Hill Companies, Inc. ISBN   0-07-049439-8.
  5. 1 2 3 Sigma-Aldrich Co., Chromium(VI) oxide. Retrieved on 2021-11-22.
  6. 1 2 3 4 "Chromium trioxide". chemicalland21.com. AroKor Holdings Inc. Retrieved 2014-06-15.
  7. 1 2 3 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1007. doi:10.1016/C2009-0-30414-6. ISBN   978-0-08-037941-8.
  8. 1 2 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.
  9. ↑ Mamyrbaev, Arstan Abdramanovich; Dzharkenov, Timur Agataevich; Imangazina, Zina Amangalievna; Satybaldieva, Umit Abulkhairovna (2015-04-16). "Mutagenic and carcinogenic actions of chromium and its compounds". Environmental Health and Preventive Medicine. 20 (3). Springer Science and Business Media LLC: 159–167. doi:10.1007/s12199-015-0458-2. ISSN   1342-078X. PMC   4434237 . PMID   25877777.
  10. ↑ 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
  11. ↑ Stephens, J. S.; Cruickshank, D. W. J. (1970). "The crystal structure of (CrO3)∞". Acta Crystallographica Section B. 26 (3): 222. doi:10.1107/S0567740870002182.
  12. ↑ Zhai, H. J.; Li, S.; Dixon, D. A.; Wang, L. S. (2008). "Probing the Electronic and Structural Properties of Chromium Oxide Clusters (CrO
    3    )−
    n     and (CrO3)n (n = 1–5): Photoelectron Spectroscopy and Density Functional Calculations". Journal of the American Chemical Society. 130 (15): 5167–77. doi:10.1021/ja077984d. PMID   18327905.
  13. ↑ Ghammamy, Shahriare; Baghy, Monir Rahnama (2008). "Using of Taguchi Method for Experimental Design of Crystallization Processes of an Oxidant: Tetraethylammonium Chlorochromate (VI)". Journal of Chemical Crystallography. 38 (12): 907–912. Bibcode:2008JCCry..38..907G. doi:10.1007/s10870-008-9403-1.
  14. ↑ "Chromium-based Reagents". Oxidation of Alcohols to Aldehydes and Ketones. Basic Reactions in Organic Synthesis. 2006. pp. 1–95. doi:10.1007/0-387-25725-X_1. ISBN   0-387-23607-4.
  15. ↑ J. C. Collins, W.W. Hess (1972). "Aldehydes from Primary Alcohols by Oxidation with Chromium Trioxide: Heptanal". Organic Syntheses. 52: 5. doi: 10.15227/orgsyn.052.0005 .
  16. ↑ "Chromium-based Reagents". Oxidation of Alcohols to Aldehydes and Ketones. Basic Reactions in Organic Synthesis. 2006. pp. 1–95. doi:10.1007/0-387-25725-X_1. ISBN   0-387-23607-4.
  17. ↑ "Chromium Trioxide (MSDS)". J. T. Baker. Archived from the original on 2015-01-12. Retrieved 2007-09-13.
  18. ↑ The environmental impact of hexavalent chromium inspired the 2000 biographical Hollywood movie Erin Brockovich .
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