/an huy"druyd, -drid/, n. Chem.1. a compound formed by removing water from a more complex compound: an oxide of a nonmetal (acid anhydride) or a metal (basic anhydride) that forms an acid or a base, respectively, when united with water.2. a compound from which water has been abstracted.[1860-65; ANHYDROUS + -IDE]
* * *Any chemical compound obtained, either in practice or in principle, by eliminating water (H2O) from another compound.Examples of inorganic anhydrides are sulfur trioxide, SO3, which is derived from sulfuric acid, H2SO4, and calcium oxide, CaO, which is derived from calcium hydroxide Ca(OH)2. The most important organic anhydride is acetic anhydride, (CH3CO)2O, a raw material for making cellulose acetate (used for films, fibres, and plastic goods) and aspirin. It can be thought of as acetic acid minus water. Organic anhydrides are very important starting materials for organic synthesis, as they can give rise to carboxylic acids, esters, or amides under the proper conditions.
* * *any chemical compound obtained, either in practice or in principle, by the elimination of water from another compound. Examples of inorganic anhydrides are sulfur trioxide, SO3, which is derived from sulfuric acid, and calcium oxide, CaO, derived from calcium hydroxide. Sulfur trioxide and other oxides formed by the removal of water from an acid are often called acid anhydrides, whereas those such as calcium oxide that are produced by a base upon the loss of water are designated basic anhydrides.The most important of the organic anhydrides is acetic anhydride, (CH3CO)2O. It is prepared industrially in either of two ways: by atmospheric oxidation of acetaldehyde in the presence of a metal acetate; and from acetic acid by reaction with acetylene or ketene. Other organic anhydrides can be prepared from carboxylic acids by reaction with acetic anhydride, ketene, methoxyacetylene, or isopropenyl acetate. Anhydrides also are produced when acyl halides react with acetic anhydride or with carboxylic acid and pyridine.The organic anhydrides are used to introduce the acyl group (RCO) in organic synthesis. They react with water to give carboxylic acids, with alcohols or phenols to give esters, and with ammonia and amines to give amides. Acetic anhydride is employed in the manufacture of cellulose acetate, which is widely used as a base for magnetic tape and in the manufacture of textile fibres. Also, it is heated with salicylic acid to produce the medicinal chemical acetylsalicylic acid (aspirin).
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