Chromium trioxide
From Wikipedia, the free encyclopedia
| Chromium trioxide | |
|---|---|
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| IUPAC name |
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| Other names | Chromic anhydride, chromium(VI) oxide, chromic acid, anhydride, chromic acid (misnomer) |
| Identifiers | |
| CAS number | [] |
| PubChem | |
| UN number | 1463 |
| RTECS number | GB6650000 |
| Properties | |
| Molecular formula | CrO3 |
| Molar mass | 99.9943 g/mol |
| Appearance | dark red granular solid |
| Odor | odorless |
| Density | 2.70 g/cm3 (20 °C) |
| Melting point |
197 °C |
| Boiling point |
251 °C, decomposes |
| Solubility in water | 61.7 g/100 mL (0 °C) 63 g/100 mL (25 °C) 67 g/100 mL (100 °C) |
| Solubility | soluble in sulfuric acid, nitric acid |
| Hazards | |
| MSDS | ICSC 1194 |
| EU Index | 024-001-00-0 |
| EU classification | Oxidizer (O) Carc. Cat. 1 Muta. Cat. 2 Repr. Cat. 3 Very toxic (T+) Dangerous for the environment (N) |
| R-phrases | R45, R46, R9, R24/25, R26, R35, R42/43, R48/23, R62, R50/53 |
| S-phrases | S53, S45, S60, S61 |
| NFPA 704 |
 1
3
1
OX
|
| LD50 | 80 mg/kg |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Chromium trioxide is the inorganic compound with the formula CrO3. It is the acid anhydride of chromic acid, and is sometimes marketed under the same name.[1] This compound is a dark red/orange brown solid, which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating.[2]
Contents |
[edit] Production, structure, and basic reactions
Chromium trioxide is generated by treating sodium chromate or the corresponding sodium dichromate with sulfuric acid:[1]
- H2SO4 + Na2CrO4 → CrO3 + Na2SO4 + H2O
Approximately 100M kg are produced annually by this or similar routes.[2]
The solid consists of chains of tetrahedrally coordinated chromium atoms that share vertices. Each chromium center therefore share two oxygen centers with neighbors. Two oxygen atoms that are not shared, giving an overall stoichiometry of 1:3.[3]
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,[3] or acetone in the case of the Jones oxidation. In these oxidations, the Cr(VI) converts 1.5 equivalents of alcohols to the corresponding ketones or aldehydes:
- 2 CrO3 + 3 RCH2OH → Cr2O3 + 3 RCHO + 3 H2O
[edit] Applications
Chromium trioxide is mainly used in chrome-plating. Typically it is 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 a passivating chromate films that resist corrosion.
[edit] Safety
Chromium trioxide is highly toxic, corrosive, and carcinogenic.[4] It is the main example of the environmental hazard known as "hexavalent chromium." 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.
[edit] References
- ^ a b "Chromium Trioxide". Chemicalland21. http://www.chemicalland21.com/industrialchem/inorganic/CHROMIUM%20TRIOXIDE.htm.
- ^ a b Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinge. Chromium Compounds. in Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, 2002. doi:10.1002/14356007.a07_067
- ^ 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
- ^ "Chromium Trioxide (MSDS)". J. T. Baker. http://www.jtbaker.com/msds/englishhtml/C4400.htm. Retrieved on 2007-09-13.
[edit] External links
- ATSDR Case Studies in Environmental Medicine: Chromium Toxicity U.S. Department of Health and Human Services
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