Propanoyl chloride Propionic anhydride is an organic compound with the formula (CH3CH2CO)2O.

This simple acid anhydride is a colourless liquid.

It is a widely used reagent in organic synthesis as well as for producing specialty derivatives of cellulose.

[1] Industrial route to propionic anhydride involves thermal dehydration of propionic acid, driving off the water by distillation: Another routes is the Reppe carbonylation of ethylene with propionic acid and nickel carbonyl as the catalyst:[1] Propionic anhydride has also been prepared by dehydration of propionic acid using ketene:[2] Propanoic anhydride is strong smelling and corrosive, and will cause burns on contact with skin.

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 Administration as a List I chemical under the Controlled Substances Act.