Organic acid anhydride

Anhydrides (usually just called anhydrides ) is the name for a group of chemical compounds that are always derivatives oxygen-containing acids. They arise formally by loss of water ( dehydration) from an acid. For inorganic oxygen acids, oxides form, such as phosphoric acid from phosphorus pentoxide. From the organic carboxylic acids are called carboxylic form. Mixed anhydrides are formed by condensation of two different acids. When mixed anhydrides can therefore interpret carbonyl halides.

Types

With organic acids ( carboxylic acids ) in the molecule two acid groups are linked via an oxygen bridge. The two acid groups can either come from a molecule (intramolecular ) as in phthalic anhydride or to two different molecules include ( intermolecular) as in acetic anhydride. Organic acids in the acid anhydride is called by the name of the acid is added the suffix anhydride.

Formally, therefore carbonyl halides anhydrides of a carboxylic acid with a hydrogen halide, for example, acetyl chloride:

For inorganic acids, the substances usually have their own name. Phosphorus, for example the acid anhydride of phosphoric acid. Mixed anhydrides arise by elimination of water from two different acids.

Representation

Anhydrides may be generated in various ways:

  • By reacting a carboxylic acid chloride with an acid or
  • By elimination of water using a strong dehydrating agent such as sulfuric acid.
  • Special anhydrides can also be produced in other ways. For example, maleic anhydride is obtained by oxidation of benzene and phthalic anhydride from naphthalene.
  • A special case is carbon monoxide; it can be produced by dehydration of formic acid and by introducing carbon monoxide in caustic soda formate. Thus, an inorganic substance is the acid anhydride of an organic.

Properties and Uses

Acid anhydrides react exothermically to whom or to the corresponding acid (s) with water. Acid anhydrides can be used for the halogen-free Friedel-Crafts acylation or the drying of the corresponding acid.

  • Substance Group
  • Oxygen compound
Dehydration reaction Condensation reaction Exothermic reaction
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