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Chromyl chloride
Wireframe model of chromyl chloride	Ball and stick model of 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 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:33038 ;
ChemSpider	21106426 ;
ECHA InfoCard	100.035.491
EC Number	239-056-8;
Gmelin Reference	2231
PubChem CID	22150757;
RTECS number	GB5775000;
UNII	JQU316FZ5W ;
UN number	1758
CompTox Dashboard (EPA)	DTXSID30894858 ;
	InChI InChI=1S/2ClH.Cr.2O/h21H;;;/q;;+2;;/p-2 Key: AHXGRMIPHCAXFP-UHFFFAOYSA-L ; InChI=1S/2ClH.Cr.2O/h21H;;;/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
	Occupational safety and health (OHS/OSH):
Main hazards	Toxic, oxidizer, carcinogenic, mutagenic, reacts violently with water
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H271, H314, H317, H340, H350, H410
Precautionary statements	P201, P210, P280, P303+P361+P353, P305+P351+P338+P310, P308+P313
NFPA 704 (fire diamond)	3 0 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.
Safety data sheet (SDS)	Sigma Aldrich - Chromyl Chloride
Related compounds
Related compounds	Sulfuryl chloride; Vanadium oxytrichloride; MoO2Cl2; Tungsten dichloride dioxide; Chromyl fluoride
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) 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. It is the dichloride of chromic acid.

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.^[3]^[4]

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

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.^[5] It will also attack benzylic methyl groups to give aldehydes via the Étard reaction. Dichloromethane is a suitable solvent for these reactions.^[6]

Others

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

Safety considerations

Chromyl chloride is severely corrosive and easily burns the skin and eyes. It is a probable human carcinogen. ^[7]

References

^ ^a ^b ^c ^d ^e ^f ^g NIOSH Pocket Guide to Chemical Hazards. "#0142". National Institute for Occupational Safety and Health (NIOSH).
^ "Chromyl chloride 200042" (PDF). Sigma-Aldrich. Archived from the original on 2020-09-01.
^ Moody, B.J. (1965). "22". Comparative Inorganic Chemistry (1 ed.). London: Edward Arnold. p. 381. ISBN 0-7131-3679-0.
^ Sisler, Harry H. (1946). Chromyl Chloride [Chromium(VI) Dioxychloride]. Inorganic Syntheses. Vol. 2. pp. 205–207. doi:10.1002/9780470132333.ch63. ISBN 9780470132333.
^ Freeman, Fillmore; DuBois, Richard H.; McLaughlin, Thomas G. (1971). "Aldehydes by Oxidation of Terminal Olefins with Chromyl Chloride: 2,4,4-Trimethylpentanal". Org. Synth. 51: 4. doi:10.15227/orgsyn.051.0004.
^ F. Freeman (2004). "Chromyl Chloride". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rc177. ISBN 0471936235.
^ Prof CH Gray, ed. (1966). "IV". Laboratory Handbook of Toxic Agents (2 ed.). London: Royal Institute of Chemistry. p. 79.