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acetic anhydride[ə′sēd·ik an′hīd‚rīd]
(CH3CO)2O, a colorless liquid with a pungent odor. Acetic anhydride is soluble in benzene, ether, and other organic solvents; it has a boiling point of 139.5°C and a density of 1.082 g/cm3 at 20°C. Acetic anhydride is one of the reactants widely used in chemical synthesis for introducing the acetyl radical (CH3CO—), a process known as acetylation. Examples are provided by the reactions with alcohols (ROH) to form esters (CH3COOR), with amines (RNH2) to form amides (CH3CONHR), and with mercaptans (RSH) to form thioethers (CH3COSR). When heated with water, acetic anhydride forms acetic acid.
In industry, acetic anhydride is obtained by such methods as the catalytic oxidation of acetaldehyde in the presence of the acetates cobalt and copper and the reaction of acetic acid with ketene. The compound is mainly used in producing cellulose acetate, acetopropionate, and acetate butyrate; these substances in turn are used in making synthetic fibers, plastic products, coatings, paints, varnishes, and the backing of photographic and motion-picture film, as well as in producing such odoriferous substances as acetanisole and such pharmaceuticals as phenacetin.