Chemistry:Chromyl chloride

Chromyl chloride

Names
Preferred IUPAC name Chromium(VI) dichloride dioxide
Systematic IUPAC name Dichloridodioxidochromium
Other names Chromic acid chloride Chromium oxychloride Etard Reagent Chlorochromic anhydride Chromic oxychloride Chromium chloride oxide Chromium dioxide dichloride Chromium dioxychloride Chromium oxychloride
Identifiers
CAS Number	14977-61-8 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:33038 Y
ChemSpider	21106426 Y
EC Number	239-056-8
Gmelin Reference	2231
PubChem CID	22150757
RTECS number	GB5775000
UNII	JQU316FZ5W Y
UN number	1758
InChI InChI=1S/2ClH.Cr.2O/h2*1H;;;/q;;+2;;/p-2 Y Key: AHXGRMIPHCAXFP-UHFFFAOYSA-L Y InChI=1S/2ClH.Cr.2O/h2*1H;;;/q;;+2;;/p-2 Key: AHXGRMIPHCAXFP-UHFFFAOYSA-L InChI=1/2ClH.Cr.2O/h2*1H;;;/q;;+2;;/p-2/rCl2CrO2/c1-3(2,4)5 Key: AHXGRMIPHCAXFP-GRYJOLFGAD
SMILES Cl[Cr](Cl)(=O)=O
Properties
Chemical formula	CrO2Cl2
Molar mass	154.9008 g/mol
Appearance	Blood-red fuming liquid, similar to bromine
Odor	Musty, burning, acrid
Density	1.911 g/mL, liquid
Melting point	−96.5 °C (−141.7 °F; 176.7 K)
Boiling point	118.5 °C (245.3 °F; 391.6 K)
Solubility in water	Reacts with water
Vapor pressure	20 mmHg (20 °C)
Hazards
Main hazards	Toxic, oxidizer, carcinogenic, mutagenic, reacts violently with water
Safety data sheet	Sigma Aldrich - Chromyl Chloride
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H271, H314, H317, H340, H350, H410
GHS precautionary statements	P201, P210, P280, P303+361+353, P305+351+338+310, P308+313
NFPA 704 (fire diamond)	0 3 2 W OX
Flash point	noncombustible
NIOSH (US health exposure limits):
PEL (Permissible)	none
REL (Recommended)	Ca TWA 0.001 mg Cr(VI)/m3
IDLH (Immediate danger)	N.D.
Related compounds
Related compounds	SO2Cl2; VOCl3; MoO2Cl2; WO2Cl2; CrO2F2
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Chromyl chloride is an inorganic compound with the formula CrO₂Cl₂. It is a reddish brown compound that is a volatile liquid at room temperature, which is unusual for transition metal compounds.

Preparation

Chromyl chloride can be prepared by the reaction of potassium chromate or potassium dichromate with hydrogen chloride in the presence of sulfuric acid, followed by distillation.

K₂Cr₂O₇ + 6 HCl → 2 CrO₂Cl₂ + 2 KCl + 3 H₂O

The sulfuric acid serves as the dehydration agent. It can also be prepared directly by exposing chromium trioxide to anhydrous hydrogen chloride gas.

CrO₃ + 2 HCl ⇌ CrO₂Cl₂ + H₂O

The method used to prepare chromyl chloride is the basis for a qualitative test for chloride: a sample suspected of containing chloride is heated with a mixture of potassium dichromate and concentrated sulfuric acid. If chloride is present, chromyl chloride forms as evidenced by red fumes of CrO₂Cl₂. Analogous compounds are not formed with fluorides, bromides, iodides and cyanides.

Usage

Test for the presence of chlorides

The chromyl chloride test involves heating a sample suspected to contain chlorides with potassium dichromate and concentrated sulfuric acid. If a chloride is present, chromyl chloride forms, its presence being indicated by the formation of red smoke. Otherwise, no red smoke will obviously appear. No similar compound is formed in the presence of fluoride, bromide, iodide, or cyanide, making this test specific to chlorides.

Reagent for oxidation of alkenes

Chromyl chloride oxidizes internal alkenes to alpha-chloroketones or related derivatives. It will also attack benzylic methyl groups to give aldehydes via the Étard reaction. Dichloromethane is a suitable solvent for these reactions.

Others

CrO₂Cl₂ can also be used to test for the absence of nitrate ions.

Safety considerations

Chromyl chloride is often stored in sealed glass ampoules to prevent vapours leaking out of the container

Chromyl chloride is severely corrosive and easily burns the skin and eyes.

External links

• CDC - NIOSH Pocket Guide to Chemical Hazards - Chromyl Chloride