Anhydride
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distinguish from anhydrite
{{Distinguish|anhydrite}}
[[Image:Generic_Anhydride.png|thumb|150px|right|Generic example of an anhydride.]]
In [[chemistry]], an '''anhydride''' is a [[Compound (chemistry)|compound]] that can be considered as derived from another compound by subtracting the molecules of [[Water (molecule)|water]].
For example:
: 2 [[sodium hydroxide|NaOH]] - H<sub>2</sub>O → [[sodium oxide|Na<sub>2</sub>O]]
: [[sulfuric acid|H<sub>2</sub>SO<sub>4</sub>]] - H<sub>2</sub>O → [[sulfur trioxide|SO<sub>3</sub>]]
Thus [[sodium oxide]] is an anhydride of [[sodium hydroxide]], and [[sulfur trioxide]] is an anhydride of [[sulfuric acid]].
In organic chemistry, the compounds most commonly involved are [[carboxylic acid]]s.
: 2 [[acetic acid|CH<sub>3</sub>COOH]] - H<sub>2</sub>O → [[acetic anhydride|(CH<sub>3</sub>CO)<sub>2</sub>O]]
Compounds involved are often [[acid]]s or [[base (chemistry)|base]]s; in such cases, the anhydrides can be called [[acid anhydride]]s or [[base anhydride]]s. This does not imply that the anhydrides are not themselves acids or bases; they are. But the more hydrated forms may be more familiar or convenient.
''Anhydride'' is sometimes used as a synonym for ''acid anhydride''.
Following are two reactions, one with a typical acid and base, one with their anhydrides. The first one is more practical.
: 2 NaOH (aq) + H<sub>2</sub>SO<sub>4</sub> (aq) → Na<sub>2</sub>SO<sub>4</sub> + 2H<sub>2</sub>O (l)
: Na<sub>2</sub>O (s) + SO<sub>3</sub> (g) → Na<sub>2</sub>SO<sub>4</sub> (aq)
In general, anhydrides are more reactive than their corresponding acids, as they can react with water to form their corresponding acid. They often are good dehydrating agents. [[Acetic anhydride]] is useful in the [[acetylation]] of salicylic acid, as using [[acetic acid]] to perform the reaction leaves water behind, which can destroy the product, acetylsalicylic acid, or [[aspirin]].
In biology, most of the [[high-energy phosphate]] compounds are formed from the condensation of the [[phosphate]] ion with a phosphorylated [[sugar]]. The resulting [[pyrophosphate]] bond is a classic anhydride bond.
==See also==
* [[Acid anhydride]]
[[Category:Chemical compounds]]
[[cs:Anhydrid]]
[[de:Anhydride]]
[[es:Anhidruro]]
[[eo:Anhidrido]]
[[fr:Anhydride]]
[[it:Anidride]]
[[he:אנהידריד]]
[[lv:Anhidrīds]]
[[nl:Anhydride]]
[[pt:Anidrido]]
[[ru:Ангидрид]]
[[sr:Анхидрид]]
[[fi:Anhydridi]]
[[sv:Anhydrid]]
[[tg:Анҳидрид]]
[[uk:Ангідрид]]