Chromyl chloride

Chromyl chloride

Chromyl chloride fuming in air
Names
Preferred IUPAC name Chromium(VI) dichloride dioxide
Systematic IUPAC name Dichlorodioxochromium
Other names Chromic oxychloride, chromium chloride oxide, chromium dioxychloride, chromium dichloride dioxide, chromium dioxide dichloride, chromium oxychloride, chlorochromic anhydride
Properties
Chemical formula	CrO2Cl2
Molar mass	154.9008 g/mol
Appearance	Viscous fuming blood-red liquid
Odor	Acrid, burning
Density	1.96 g/cm3 (at 20 °C)
Melting point	−96.5 °C (−141.7 °F; 176.7 K)
Boiling point	117 °C (243 °F; 390 K)
Solubility in water	Reacts
Solubility	Reacts with alcohols, toluene Soluble in glacial acetic acid, benzene, carbon disulfide, carbon tetrachloride, chloroform, dichloromethane, diethyl ether, nitrobenzene, phosphoryl chloride
Vapor pressure	20 mmHg (at 20 °C)
Hazards
Safety data sheet	Acros
Flash point	Non-flammable
Related compounds
Related compounds	Chromic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chromyl chloride is an inorganic chemical compound, used as an oxidizing agent, mostly in organic chemistry. It is an opaque dark blood-red liquid at standard conditions.

Properties

Chemical

Chromyl chloride will oxidize toluene to benzaldehyde. This reaction occurs in two steps:

First, a chromium compound is formed from the chromyl chloride and toluene:

C₆H₅CH₃ + 2 CrO₂Cl₂ → C₆H₅CH[CrO₂Cl₂]₂

The complex is hydrolyzed with water to yield benzaldehyde.

C₆H₅CH[CrO₂Cl₂]₂ + 2 H₂O → C₆H₅CH=O + Cr₂O₃ + 4 HCl

It will react with water to yield chromic acid and hydrochloric acid. The reaction is exothermic.

CrO₂Cl₂ + 2 H₂O → H₂CrO₄ + 2 HCl

Physical

Chromyl chloride is a deep red viscous liquid, which fumes in air. It reacts with water, alcohols, but soluble in chlorinated carbons and carboxylic acids.

Availability

Chromyl chloride is difficult to find and due to its hazards, it's difficult to acquire in most countries. It's best to make it yourself, though you better have a good ventilation if you attempt to make it, as it's a nasty thing.

Preparation

Chromyl chloride can be made by reacting potassium dichromate with sulfuric acid and sodium chloride:

K₂Cr₂O₇ + 4 NaCl + 6 H₂SO₄ → 2 CrO₂Cl₂ + 2 KHSO₄ + 4 NaHSO₄ + 3 H₂O

A good procedure can be found here.

Chromium trioxide or potassium chromate can also be used instead of potassium dichromate.

Projects

• Make benzaldehyde
• Spontaneous ignition of sulfur

Handling

Safety

Chromyl chloride is extremely corrosive and will fume in contact with air, releasing a mist of hydrochloric and chromic acids. Proper protection must be worn when handling the compound. As it is a Cr(VI) compound, it is also carcinogenic.

Storage

Chromyl chloride must be stored in glass containers, with a proper label and a hazard symbol, away from any moisture or organic compounds. A round bottom flask with a glass stopper can be used. Inspect it periodically to make sure there's no leak and check if the ground joint froze.

Disposal

To safely neutralize chromyl chloride, add the compound in a chilled inert solvent, like chloroform or glacial acetic acid and stir the suspension/solution. Slowly add a reducing agent, such as sodium sulfite/metabisulfite/thiosulfate, ascorbic acid or glucose/sugar until the color changes from red/orange to green. Try to avoid adding aqueous solutions if possible, especially if you're using glacial acetic acid as solvent, as the neutralization will generate heat.

Do this outside or in a fumehood, wearing proper protection.

References

Relevant Sciencemadness threads

• Demo with chromyl chloride
• Improving the yield of chromyl chloride: various questions