Chromyl chloride

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 Dichlorodioxochromium
	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;
PubChem CID	22150757;
RTECS number	GB5775000;
UNII	JQU316FZ5W ;
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[1]
Density	1.911 g/mL, liquid
Melting point	-96.5 °C
Boiling point	117 °C
Solubility in water	Very soluble,hydrolysis
Vapor pressure	20 mmHg (20 °C)[1]
Hazards
Main hazards	carcinogen, reacts violently with water[1]
GHS pictograms	[2]
NFPA 704 (fire diamond)	0 3 2 W; OX
Flash point	noncombustible [1]
	NIOSH (US health exposure limits):
PEL (Permissible)	none[1]
REL (Recommended)	Ca TWA 0.001 mg Cr(VI)/m3[1]
IDLH (Immediate danger)	N.D.[1]
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 a chemical compound with the formula CrO₂Cl₂. The molecule is tetrahedral, like most of the commonly encountered chromium(VI) derivatives such as chromate, [CrO₄]²⁻. In terms of physical properties and structure, it resembles sulfuryl chloride. It is a hygroscopic dark red liquid, that in terms of color and volatility has also been described as resembling bromine.[3]

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 gentle distillation.[4][3]

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.

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]

Safety considerations

CrO₂Cl₂ hydrolyzes to release hydrochloric acid (HCl) and hexavalent chromium (Cr^VI)

Acute: Exposure to chromyl chloride vapour irritates the respiratory system and severely irritates the eyes, and the liquid burns the skin and eyes. Ingestion would cause severe internal damage.[7]

Chronic: Cr^VI can produce chromosomal aberrations and is a human carcinogen via inhalation.[8] Frequent exposure of the skin to chromyl chloride may result in ulceration.[7]

References

NIOSH Pocket Guide to Chemical Hazards. "#0142". National Institute for Occupational Safety and Health (NIOSH).
Sisler, Harry H. (1946). "Chromyl Chloride [Chromium(VI) Dioxychloride]". Inorganic Syntheses. 2: 205–207. doi:10.1002/9780470132333.ch63.
Moody, B.J. (1965). "22". Comparative Inorganic Chemistry (1 ed.). London: Edward Arnold. p. 381. ISBN 0-7131-3679-0.
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..}}
Prof CH Gray, ed. (1966). "IV". Laboratory Handbook of Toxic Agents (2 ed.). London: Royal Institute of Chemistry. p. 79.
IARC (1999-11-05) [1990]. Volume 49: Chromium, Nickel, and Welding (PDF). pp. 21–23. ISBN 92-832-1249-5. Archived from the original (PDF) on 2008-12-24. Retrieved 2008-03-26.

External links

CDC - NIOSH Pocket Guide to Chemical Hazards - Chromyl Chloride

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[PGCH-1] NIOSH Pocket Guide to Chemical Hazards. "#0142". National Institute for Occupational Safety and Health (NIOSH).

[Sis-3] Sisler, Harry H. (1946). "Chromyl Chloride [Chromium(VI) Dioxychloride]". Inorganic Syntheses. 2: 205–207. doi:10.1002/9780470132333.ch63.

[4] Moody, B.J. (1965). "22". Comparative Inorganic Chemistry (1 ed.). London: Edward Arnold. p. 381. ISBN 0-7131-3679-0.

[5] 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.

[6] F. Freeman (2004). "Chromyl Chloride". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rc177..}}

[Gray1966-7] Prof CH Gray, ed. (1966). "IV". Laboratory Handbook of Toxic Agents (2 ed.). London: Royal Institute of Chemistry. p. 79.

[8] IARC (1999-11-05) [1990]. Volume 49: Chromium, Nickel, and Welding (PDF). pp. 21–23. ISBN 92-832-1249-5. Archived from the original (PDF) on 2008-12-24. Retrieved 2008-03-26.