CrO3H2SO4

CrO3H2SO4 is an adduct formed from chromium trioxide (CrO3) and sulfuric acid (H2SO4). It is often described by the formula CrO3·H2SO4 and is encountered as a crystalline solid that can be prepared by combining CrO3 with concentrated sulfuric acid at low temperature.

The compound is typically made by adding CrO3 to cold, concentrated H2SO4 and allowing the mixture to form a solid adduct. In the solid, the Cr(VI) center is coordinated within a network that involves sulfate-derived oxygens, with the 1:1 CrO3:H2SO4 composition commonly cited, though crystal form can influence the precise arrangement. It is most stable in strongly acidic media and is usually handled under such conditions.

CrO3H2SO4 is a strong oxidizing agent and is highly reactive in concentrated sulfuric acid. It is hygroscopic and tends to be soluble in the acid medium but not in water. Upon heating or upon addition of water, it can decompose, regenerating CrO3 and H2SO4 or forming other Cr(VI) oxide-sulfate species.

In practical use, the CrO3–H2SO4 adduct serves as a source of chromium trioxide in highly acidic environments and is related to oxidations carried out with Jones-type reagents. It has historical relevance in organic synthesis as a robust oxidant under strongly acidic conditions.

Safety: Chromium(VI) compounds are toxic and carcinogenic. CrO3 and its sulfuric acid adduct are strong oxidizers and corrosive. Handle in a fume hood with appropriate protective equipment to avoid inhalation, ingestion, or contact with skin or eyes.