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Chromyl chloride

Chromium oxychloride Chromic oxychloride Étard reagent Chlorochromic anhydride Chromium chloride oxide Chromium dioxide dichloride Chromium dioxychloride |NFPA-H = 3 |NFPA-F = 0 |NFPA-R = 2 |NFPA-S = W+OX Vanadium oxytrichloride Molybdenum dichloride dioxide Tungsten dichloride dioxide Chromyl fluoride Uranyl chloride}}

Chromyl chloride is an inorganic compound with the formula CrO2Cl2 and is the formal dichloride of chromic acid. 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 concentrated sulfuric acid, followed by distillation. :K2Cr2O7 + 6 HCl → 2 CrO2Cl2 + 2 KCl + 3 H2O The sulfuric acid serves as a dehydration agent. This reaction, the chloride test, gives a strikingly red product. It was once used as a test for chloride. No similar compound is formed in the presence of fluoride, bromide, iodide, or cyanide, making this test specific to chlorides.

It can also be prepared directly by exposing chromium trioxide to anhydrous hydrogen chloride gas. :CrO3 + 2 HCl ⇌ CrO2Cl2 + H2O

When trityl chloride is used in place of HCl, the products are CrO2Cl2, trityl chlorochromate CrO2Cl(OCPh3) and chromate CrO2(OCPh3)2 (Ph = C6H5).

Reactions

Chromyl chloride is a Lewis acid, and a highly aggressive oxidant. It reacts with cyclohexane to give chlorocyclohexane, chlorocyclohexanone, and other species.

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.

When treated with conventional Lewis bases, chromyl chloride forms adducts, such as CrO2Cl2(2,2'-bipy): :

Safety considerations

Main article: Hexavalent chromium

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

References

References

  1. "Chromyl chloride 200042".
  2. {{PGCH. 0142
  3. {{Greenwood&Earnshaw2nd
  4. Moody, B.J.. (1965). "Comparative Inorganic Chemistry". Edward Arnold.
  5. (1946). "Inorganic Syntheses".
  6. (1990). "Chromyl Complexes with Aryloxy and Siloxy Ligands". Inorganic Chemistry.
  7. (2010). "C−H Bond Activations by Metal Oxo Compounds". Chemical Reviews.
  8. (1971). "Aldehydes by Oxidation of Terminal Olefins with Chromyl Chloride: 2,4,4-Trimethylpentanal". Org. Synth..
  9. F. Freeman. (2004). "Encyclopedia of Reagents for Organic Synthesis".
  10. (2014). "Synthesis, Properties, and Structures of Chromium(VI) and Chromium(V) Complexes with Heterocyclic Nitrogen Ligands". Zeitschrift für Anorganische und Allgemeine Chemie.
  11. (1966). "Laboratory Handbook of Toxic Agents". [[Royal Institute of Chemistry]].
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chromium(vi)-compounds chromium–halogen-compounds oxychlorides oxidizing-agents carcinogens chromium–oxygen-compounds
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