Difference between revisions of "Chromium trioxide"

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| OtherNames = Chromic anhydride<br>Chromic acid anhydride<br>Chromium(VI) oxide
 
| OtherNames = Chromic anhydride<br>Chromic acid anhydride<br>Chromium(VI) oxide
 
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| ImageFile = Crude chromium trioxide by Doug's Lab.png
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| SolubleOther = Soluble in [[acetic acid]], [[acetone]], [[diethyl ether]], [[nitric acid]], [[sulfuric acid]]
 
| SolubleOther = Soluble in [[acetic acid]], [[acetone]], [[diethyl ether]], [[nitric acid]], [[sulfuric acid]]
 
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| Solvent =  
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| VaporPressure = ~0 mmHg
 
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| AutoignitionPt = Non-flammable
 
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| ExternalMSDS = [http://www.sciencelab.com/msds.php?msdsId=9923475 ScienceLab]
 
| ExternalMSDS = [http://www.sciencelab.com/msds.php?msdsId=9923475 ScienceLab]
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| FlashPt = Non-flammable
 
| LD50 = 80 mg/kg (rats, oral)
 
| LD50 = 80 mg/kg (rats, oral)
 
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| MainHazards = Oxidizer
 
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==Properties==
 
==Properties==
 
===Chemical===
 
===Chemical===
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Chromium trioxide reacts violently with [[ethanol]] and other organic compounds, causing it to combust.
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Chromium trioxide decomposes above 197 °C, yielding chromium(III) oxide and liberating [[oxygen]]:
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: 4 CrO<sub>3</sub> → 2 Cr<sub>2</sub>O<sub>3</sub> + 3 O<sub>2</sub>
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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 alcohol]]s to the corresponding [[carboxylic acid]]s and [[secondary alcohol]]s to [[ketone]]s.<ref>Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience</ref> The reactions are shown below:
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 +
Primary alcohols to carboxylic acids:
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: 4 CrO<sub>3</sub> + 3 RCH<sub>2</sub>OH + 12 H<sup>+</sup> → 3 RCOOH + 4 Cr<sup>3+</sup> + 9 H<sub>2</sub>O
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 +
Secondary alcohols to ketones:
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: 2 CrO<sub>3</sub> + 3 R<sub>2</sub>CHOH + 6 H<sup>+</sup> → 3 R<sub>2</sub>C=O + 2 Cr<sup>3+</sup> + 6 H<sub>2</sub>O
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Dry chromium trioxide reacts violently with [[ethanol]] and other organic compounds, causing them to combust on contact.
  
 
===Physical===
 
===Physical===
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==Projects==
 
==Projects==
 
*Chrome plating
 
*Chrome plating
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*Instantaneous ignition of alcohols
  
 
==Handling==
 
==Handling==
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===Storage===
 
===Storage===
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Chromium trioxide should be stored in closed containers, away from any organic material and moisture.
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Chromium trioxide should be kept in plastic or glass containers, with a proper label and a hazard symbol, in a dry place. If you're using glass, a good idea would be to keep the glass container inside a plastic container.
 +
 
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Since the compound ignites alcohols on contact, keep it away from any source of volatile solvents or products containing alcohols.
  
 
===Disposal===
 
===Disposal===
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A reducing agent, such as [[sodium metabisulfite]], [[sodium sulfite]] or [[sodium thiosulfate]] can be used to turn CrO<sub>3</sub> into the less toxic Cr(III) oxide.
+
A reducing agent, such as [[sodium metabisulfite]], [[sodium sulfite]] or [[sodium thiosulfate]] can be used to turn CrO<sub>3</sub> into the less toxic Cr(III) oxide. [[Glucose]] may also be used, albeit in a diluted solution. The neutralization must be done outside or in a fumehood, as the process will release Cr(VI) aerosoles, which are harmful and carcinogenic.
  
 
==References==
 
==References==

Latest revision as of 20:21, 30 August 2023

Chromium trioxide
Crude chromium trioxide by Doug's Lab.png
Impure chromium trioxide
Names
IUPAC name
Chromium trioxide
Other names
Chromic anhydride
Chromic acid anhydride
Chromium(VI) oxide
Identifiers
Jmol-3D images Image
Properties
CrO3
Molar mass 99.99 g/mol
Appearance Dark red solid
Odor Odorless
Density 2.7 g/cm3 (at 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 acetic acid, acetone, diethyl ether, nitric acid, sulfuric acid
Vapor pressure ~0 mmHg
Thermochemistry
73.2 J/mol·K
−589.3 kJ/mol
Hazards
Safety data sheet ScienceLab
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
80 mg/kg (rats, oral)
Related compounds
Related compounds
 Chromium(III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chromium trioxide is an inorganic compound with the formula CrO3. It is a dark red/crimson solid, widely used in synthesis and industry. It is the acidic anhydride of chromic acid.

Properties

Chemical

Chromium trioxide decomposes above 197 °C, yielding chromium(III) oxide and liberating oxygen:

4 CrO3 → 2 Cr2O3 + 3 O2

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.[1] The reactions are shown below:

Primary alcohols to carboxylic acids:

4 CrO3 + 3 RCH2OH + 12 H+ → 3 RCOOH + 4 Cr3+ + 9 H2O

Secondary alcohols to ketones:

2 CrO3 + 3 R2CHOH + 6 H+ → 3 R2C=O + 2 Cr3+ + 6 H2O

Dry chromium trioxide reacts violently with ethanol and other organic compounds, causing them to combust on contact.

Physical

Chromium trioxide is a dard red/crimson solid in its anhydrous form, and red-orange in aqueous solution. It is very soluble in water and soluble in some organic solvents, such as acetone or diethyl ether, as well as sulfuric acid.

Availability

Chromium trioxide is sold by various chemical suppliers, though due to its hazards it's not easy to get hold of.

Preparation

Chromium trioxide can be prepared by reacting a Cr(VI) containing compound, such as sodium chromate or dichromate with concentrated sulfuric acid.

H2SO4 + Na2CrO4 → CrO3 + Na2SO4 + H2O
H2SO4 + Na2Cr2O7 → 2 CrO3 + Na2SO4 + H2O

The solid compound is filtered using a fritted funnel.

Projects

  • Chrome plating
  • Instantaneous ignition of alcohols

Handling

Safety

Chromium trioxide is a powerful oxidizer, highly toxic, corrosive, and carcinogenic. Avoid contact with alcohols.

Storage

Chromium trioxide should be kept in plastic or glass containers, with a proper label and a hazard symbol, in a dry place. If you're using glass, a good idea would be to keep the glass container inside a plastic container.

Since the compound ignites alcohols on contact, keep it away from any source of volatile solvents or products containing alcohols.

Disposal

A reducing agent, such as sodium metabisulfite, sodium sulfite or sodium thiosulfate can be used to turn CrO3 into the less toxic Cr(III) oxide. Glucose may also be used, albeit in a diluted solution. The neutralization must be done outside or in a fumehood, as the process will release Cr(VI) aerosoles, which are harmful and carcinogenic.

References

  1. ↑ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience

Relevant Sciencemadness threads

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