Anhydride
Related Category: Compounds and Elements
(ănhī´drīd, –drĭd) [Gr.,=without water], chemical compound formed by removing water, H
2O, from another compound; the anhydride can also react with water to form the original compound. An acid anhydride reacts with water to form an acid; e.g., sulfur trioxide, SO
3, reacts with water to form sulfuric acid, H
2SO
4. A basic anhydride reacts with water to form a base; e.g., calcium oxide, CaO, reacts with water to form calcium hydroxide, Ca(OH)
2. Anhydrides of organic acids have many uses. They react with alcohols to form esters; e.g., acetic anhydride, (CH
3CO)
2O, reacts with ethanol, C
2H
5OH, to form ethyl acetate, CH
3COOC
2H
5, a useful solvent. They also react with ammonia and primary or secondary amines to form amides. Other important acid anhydrides include maleic anhydride and phthalic anhydride.
