Ac2O

Ac2O is the common abbreviation for acetic anhydride, also known as ethanoic anhydride. It is a colorless, volatile liquid with a characteristic pungent, vinegar-like odor. Its molecular formula is C4H6O3 and its molecular weight is 102.09 g/mol. Ac2O is typically prepared industrially via the ketene process, in which acetic acid is converted to ketene (CH2CO) and then reacts with another molecule of acetic acid to form acetic anhydride. It can also be produced from acetic acid and acetylating reagents under controlled conditions.

Ac2O is widely used as an acetylating agent in organic synthesis. It transfers acetyl groups to alcohols to form esters, to amines to form amides, and to phenols in various acetylation reactions. It is a key reagent in the manufacture of pharmaceuticals, fragrances, and cellulose derivatives, including cellulose acetate products such as cellulose triacetate. In addition to its role in synthesis, it serves as a solvent and intermediate in several industrial processes.

Safety and handling: acetic anhydride is corrosive and poses risks to the skin, eyes, and respiratory system. It reacts with water and moisture to form acetic acid and heat, so it is moisture-sensitive and typically stored in moisture-free conditions in tightly closed containers, under appropriate ventilation. It should be handled in a well-ventilated area, away from incompatible materials, with appropriate personal protective equipment.