Acetic anhydride is an esterification agent for use in prepn. of modified food starch and for acetylation of monoglycerides. Acetic anhydride is a versatile reagent for acetylations, the introduction of acetyl groups to organic substrates. Acetic anhydride is the chemical compound with the formula (CH3CO)2O (commonly abbreviated Ac2O). Ac2O is mainly used for acetylations leading to commercially significant materials. Its largest application is for the conversion of cellulose to cellulose acetate, which is a component of photographic film and other coated materials. Similarly it is used in the production of aspirin, acetyl salicylic acid, which is prepared by the acetylation of salicylic acid. It is also used as a wood preservative via autoclave impregnation to make a longer lasting timber. Ac2O is also used in many industrial processes for the production of plastics, textiles, dyes, photochemical agents, perfumes, explosives and cigarette filters. Because of its use for the synthesis of heroin by the diacetylation of morphine, acetic anhydride (known as 'AA' in clandestine chemistry circles) is listed as a U.S. DEA List II Precursor, and restricted in many other countries.