Anhydrides (Anhydrides) is a certain oxygen-containing acid to remove one or several molecules of water, the remaining part. Generally, an inorganic acid is one molecule of the acid, and the acid anhydride of the acid is formed by directly losing one molecule of water, and the valence of the acid-determining element in the acid anhydride remains unchanged. The organic acid is formed by the dehydration reaction between two molecules of the acid or multiple molecules of the acid. Only oxygen acids have anhydrides. Anaerobic acid has no anhydride.
Anhydrides can generally be regarded as oxides formed by acid dehydration (anhydrides of organic acids are not oxides). Many can react with water to form the original acid. According to the nature of the acid, it can be divided into: (1) Anhydride of inorganic acid, which is formed by the shrinkage of one or two acid molecules. For example, carbon (acid) anhydride is carbon dioxide CO2, nitric (acid) anhydride is dinitrogen pentoxide N2O5. (2) Anhydride of organic acid, a compound formed by the condensation of two monobasic acid molecules or one dibasic acid molecule. Although it is not an oxide, it is also called anhydride. For example, acetic anhydride (CH3CO)2O, phthalic anhydride C8H4O3 and so on.