Chromyl_chloride

Chromyl chloride

Chromyl chloride

Chemical compound

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.

Quick Facts Names, Identifiers ...

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.

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

Main article: Hexavalent chromium
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.[7]

References

Wikimedia Commons has media related to Chromyl chloride.
  1. [1]
    NIOSH Pocket Guide to Chemical Hazards. "#0142". National Institute for Occupational Safety and Health (NIOSH).
  2. [2]
    "Chromyl chloride 200042" (PDF). Sigma-Aldrich. Archived from the original on 2020-09-01.
  3. [3]
    Moody, B.J. (1965). "22". Comparative Inorganic Chemistry (1 ed.). London: Edward Arnold. p. 381. ISBN 0-7131-3679-0.
  4. [4]
    Sisler, Harry H. (1946). Chromyl Chloride [Chromium(VI) Dioxychloride]. Inorganic Syntheses. Vol. 2. pp. 205–207. doi:10.1002/9780470132333.ch63. ISBN 9780470132333.
  5. [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. [6]
    F. Freeman (2004). "Chromyl Chloride". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rc177. ISBN 0471936235.
  7. [7]
    Prof CH Gray, ed. (1966). "IV". Laboratory Handbook of Toxic Agents (2 ed.). London: Royal Institute of Chemistry. p. 79.
Share this article:

This article uses material from the Wikipedia article Chromyl_chloride, and is written by contributors. Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.