Chromyl chloride

Chromyl chloride is the 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 complexes.

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
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.035.491
EC Number
  • 239-056-8
2231
RTECS number
  • GB5775000
UNII
UN number 1758
Properties
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
Very soluble,hydrolysis
Vapor pressure 20 mmHg (20 °C)[1]
Hazards
Main hazards carcinogen, reacts violently with water[1]
Safety data sheet Sigma Aldrich - Chromyl Chloride
GHS pictograms
GHS Signal word Danger
H271, H314, H317, H340, H350, H410
P201, P210, P280, P303+361+353, P305+351+338+310, P308+313[2]
NFPA 704 (fire diamond)
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

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

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

CrO2Cl2 hydrolyzes to release hydrochloric acid (HCl) and chromic acid (H2CrO4).

Acute: Exposure to chromyl chloride vapor 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: CrVI 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
  1. NIOSH Pocket Guide to Chemical Hazards. "#0142". National Institute for Occupational Safety and Health (NIOSH).
  2. "Chromyl chloride 200042" (PDF). Sigma-Aldrich. Archived from the original on 2020-09-01.
  3. Moody, B.J. (1965). "22". Comparative Inorganic Chemistry (1 ed.). London: Edward Arnold. p. 381. ISBN 0-7131-3679-0.
  4. Sisler, Harry H. (1946). "Chromyl Chloride [Chromium(VI) Dioxychloride]". Inorganic Syntheses. 2: 205–207. doi:10.1002/9780470132333.ch63.
  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..}}
  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.
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