Acid Anhydride
Definition and meaning of Acid Anhydride in chemistry.
An acid anhydride is a compound that produces an acid when it reacts with water. The term covers both an inorganic acidic oxide, such as sulfur trioxide or carbon dioxide, and an organic carboxylic acid anhydride with the general formula (RCO)2O, formed by removing water from two carboxylic acid molecules.
In more detail
Inorganic acid anhydrides are nonmetal oxides, the 'without water' form of an oxoacid; sulfur trioxide, for example, is the anhydride of sulfuric acid. Organic acid anhydrides join two acyl groups through an oxygen atom and are reactive acylating agents that readily hydrolyze back to carboxylic acids. In both senses, adding water reverses the anhydride and regenerates the parent acid.
Key facts
| Inorganic sense | An acidic (nonmetal) oxide |
|---|---|
| Organic formula | (RCO)2O |
| Reaction with water | Forms the parent acid |
| Field | General Chemistry |
Sulfur trioxide reacts with water to form sulfuric acid (SO3 + H2O → H2SO4), and acetic anhydride hydrolyzes to two molecules of acetic acid.
Frequently asked questions
What is the anhydride of an acid?
It is the compound that forms that acid when water is added. For example, carbon dioxide is the anhydride of carbonic acid, and sulfur trioxide is the anhydride of sulfuric acid.
How is an organic acid anhydride formed?
By removing a molecule of water from two carboxylic acid molecules, which links their acyl groups through a shared oxygen atom.