An acid anhydride is a member of a class of organic compounds derived formally
(but not in practise) from carboxylic acids by the elimination of water. Acid anhydrides have the general formula RCOOCOR'
and are prepared by reaction of an acid
chloride with a carboxylate. Chemically, acid anhydrides resemble acid
chlorides but are less violently reactive. They are used in the Friedel-Crafts
reaction and Diels-Alder reaction and to make esters.