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.
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.
The sulfuric acid serves as the dehydration agent. It can also be prepared directly by exposing chromium trioxide to anhydrous hydrogen chloride gas.
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. It will also attack benzylic methyl groups to give aldehydes via the Étard reaction. Dichloromethane is a suitable solvent for these reactions.
Safety considerations.
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.
Chronic: CrVI can produce chromosomal aberrations and is a human carcinogen via inhalation. Frequent exposure of the skin to chromyl chloride may result in ulceration.