Propanoic anhydride

Propanoic anhydride, also called propionic anhydride, is a simple acid anhydride. With the chemical formula (CH₃CH₂CO)₂O, it is a widely used reagent in organic synthesis.

Propionic anhydride has been prepared by dehydration of propionic acid using ketene:^[1]

2 CH₃CH₂CO₂H + CH₂=C=O → (CH₃CH₂CO)₂O + CH₃CO₂H

Propanoic anhydride is strong smelling and corrosive, and will cause burns on contact with skin. Vapour can burn eyes and lungs.

Due to its potential use as a precursor in the synthesis of fentanyl and fentanyl analogs, propanoic anhydride is regulated by the United States Drug Enforcement Agency as a List I chemical under the Controlled Substances Act.^[2]