Acid anhydrides

Acid anhydrides are a class of organic compounds that are derived from acids (including inorganic acids) by removal of a molecule of water. They are a type of functional group that result from the condensation of two carboxylic acids.

Structure and bonding

Acid anhydrides consist of two acyl groups attached to the same oxygen atom. The central atom, usually oxygen, is sp2 hybridized and has a planar molecular geometry. The C–O–C linkage is characterized by its strength and resistance to hydrolysis.

Nomenclature

The systematic name of an acid anhydride is formed by replacing the word 'acid' in the name of the parent acid by 'anhydride'. If the anhydride is formed from two different acids, the two acid names are combined in alphabetical order, followed by 'anhydride'.

Preparation

Acid anhydrides are typically prepared by dehydrating the corresponding acid. This can be achieved by heating the acid with a suitable dehydrating agent or by subjecting it to a high vacuum.

Reactions

Acid anhydrides are reactive towards nucleophiles, including water, alcohols, and amines. The reaction with water regenerates the parent acid. With alcohols and amines, acid anhydrides form esters and amides, respectively, which are classes of compounds that have wide applications in industry and biochemistry.

Uses

Acid anhydrides are used in a variety of applications in industry. They are used in the manufacture of plastics, resins, dyes, and pharmaceuticals. They are also used as laboratory reagents.

Safety

Like other acyl derivatives, acid anhydrides are often irritants and can cause burns. They are also potentially harmful if inhaled, ingested, or come into contact with the skin.

See also

• Acyl group
• Carboxylic acid
• Ester
• Amide