Chromyls

Chromyls refers to a class of chemical compounds containing the chromyl cation, CrO2^2+. This cation is characterized by a chromium atom in the +6 oxidation state, bonded to two oxygen atoms. The chromyl cation is typically found in the form of chromyl halides, such as chromyl chloride (CrO2Cl2) and chromyl bromide (CrO2Br2).

Chromyl chloride is a reddish-brown, volatile liquid that is a strong oxidizing agent. It is synthesized by reacting chromium trioxide with concentrated hydrochloric acid or by the reaction of potassium dichromate with hydrochloric acid. Chromyl chloride has been used in organic synthesis for the oxidation of certain functional groups. For example, it can be used to oxidize methyl groups attached to aromatic rings to aldehydes, a reaction known as the Étard reaction. However, due to its hazardous nature and the availability of safer alternatives, its use in laboratories is limited.

Chromyl bromide is a less common analog of chromyl chloride and shares similar properties as a strong oxidizing agent. The chromyl cation itself is unstable and readily reacts with water. The bonding within the chromyl cation is complex, with evidence suggesting a double bond between chromium and oxygen, in addition to sigma bonds. The structure is typically described as linear, with the two oxygen atoms and the chromium atom forming a straight line.