Chromyl chloride


Chromyl chloride is a reddish-brown compound of chromium with oxygen and chlorine. The compound is extremely corrosive and will readily generate reddish brown fumes in air. It is also highly carcinogenic.

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.
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 and hexavalent chromium
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.
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.