Acid Anhydride

"An acid anhydride is an organic compound that has two acyl groups bound to the same oxygen atom.^[1] Most commonly, the acyl groups are derived from the same carboxylic acid, the formula of the anhydride being (RC(O))₂O. Symmetrical acid anhydrides of this type are named by replacing the word acid in the name of the parent carboxylic acid by the word anhydride.^[2] Thus, (CH₃CO)₂O is called acetic anhydride. Mixed (or unsymmetrical) acid anhydrides, such as acetic formic anhydride (see below), are known."

"Acid anhydrides are prepared in industry by diverse means. Acetic anhydride is mainly produced by the carbonylation of methyl acetate.^[5] Maleic anhydride is produced by the oxidation of benzene or butane. Laboratory routes emphasize the dehydration of the corresponding acids. The conditions vary from acid to acid, but phosphorus pentoxide is a common dehydrating agent:"

2 CH₃COOH + P₄O₁₀ → CH₃C(O)OC(O)CH₃ + (HO)₂P₄O₉