The nomenclature of organic acid anhydrides is derived from the names of the constituent carboxylic acids. In symmetrical acid anhydrides, only the prefix of the original carboxylic acid is used and the suffix "anhydride" is added. For most unsymmetrical acid anhydrides - also called mixed anhydrides- the prefixes from both acids reacted are listed before the suffix, e.g., benzoic propanoic anhydride.