Chromium trioxide
IUPAC name	Chromium trioxide Chromium(VI) oxide
Other names	Chromic anhydride, chromium(VI) oxide, chromic acid, anhydride, chromic acid (misnomer)
Identifiers
CAS number	1333-82-0 Y
PubChem	14915
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
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 1 Production, structure, and basic reactions 2 Applications 3 Safety 4 References 5 External links

[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

[edit] External links

• ATSDR Case Studies in Environmental Medicine: Chromium Toxicity U.S. Department of Health and Human Services

v • d • e   Chromium compounds Cr(CO)6 · CrCl2 · CrCl3 · CrCl4 · CrF3 · CrN · Cr(NO3)3 · CrO · CrO2 · CrO3 · Cr2O3 · Cr2S3 · Cr2(SO4)3 · Cr3C2