Acid anhydride 1696980 222067669 2008-06-27T12:08:46Z 207.203.88.15 Neatened up and deleted redundant acetic anhydride formula (para 1 last sentence) [[Image:Carboxylic-acid-anhydride.png|thumb]] An '''acid anhydride''' is an [[organic compound]] that has two [[acyl group]]s [[Chemical bond|bound]] to the same [[oxygen]] atom.<ref name="Gold">{{GoldBookRef|title=acid anhydrides|url=http://goldbook.iupac.org/A00072.html}}</ref> Most commonly, the acyl groups are derived from the same [[carboxylic acid]], the formula of the anhydride being (RC(O))<sub>2</sub>O. Symmetrical acid anhydrides of this type are named by replacing the word ''acid'' in the name of the parent carboxylic acid by the word ''anhydride''.<ref name="Blue">{{BlueBookRef|rec=R-5.7.7|pages=123–25}}</ref> Thus, (CH<sub>3</sub>CO)<sub>2</sub>O is called ''acetic anhydride.'' Mixed (or unsymmetrical) acid anhydrides, such as acetic formic anhydride (see below), are known. ==Important acid anhydrides== [[Acetic anhydride]] is a major industrial chemical widely used for preparing acetate esters. The cyclic acid anhydride [[maleic anhydride]] is used in [[organic synthesis]] as [[dienophile]] in the [[Diels-Alder reaction]]. One or both acyl groups of an acid anhydride may also be derived from a [[sulfonic acid]] or a [[phosphonic acid]]. The mixed anhydride [[1,3-bisphosphoglycerate]] is an intermediate in the formation of ATP via [[glycolysis]].<ref>Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.</ref> == Preparation == Acid anhydrides are prepared in industry by diverse means. Acetic anhydride is mainly produced by the [[carbonylation]] of [[methyl acetate]].<ref>Zoeller, J. R.; Agreda, V. H.; Cook, S. L.; Lafferty, N. L.; Polichnowski, S. W.; Pond, D. M. "Eastman Chemical Company Acetic Anhydride Process" Catalysis Today (1992), volume 13, pp.73-91. doi:10.1016/0920-5861(92)80188-S</ref> [[Maleic anhydride]] is produced by the oxidation of [[butane]]. For pedogical and practical considerations, laboratory routes emphasize the dehydration of the corresponding acids. The conditions vary from acid to acid, but [[phosphorus pentoxide]] is a common [[dehydrating agent]]: :2 [[Acetic acid|CH<sub>3</sub>COOH]] + P<sub>4</sub>O<sub>10</sub> → [[Acetic anhydride|CH<sub>3</sub>C(O)OC(O)CH<sub>3</sub>]] + "(HO)<sub>2</sub>P<sub>4</sub>O<sub>9</sub>" Acid chlorides are also effective precursors:<ref>{{OrgSynth | author = Lewis I. Krimen | title = Acetic Formic Anhydride | collvol = 6 | collvolpages = 8| year = 1988 | prep = CV6P0008}}</ref> :CH<sub>3</sub>C(O)Cl + [[sodium formate|HCO<sub>2</sub>Na]] → HCO<sub>2</sub>COCH<sub>3</sub> + NaCl == Reactions == Acid anhydrides are a source of reactive acyl groups, and their reactions and uses resemble those of [[acyl halide]]s. In reactions with protic substrates, the reactions afford equal amounts of the acylated product and the carboxylic acid: :RC(O)OC(O)R + HY → RC(O)Y + RCO<sub>2</sub>H for HY = H<sub>2</sub>O, HOR (alcohols), HNR'<sub>2</sub> (ammonia, primary, secondary amines), aromatic ring (see [[Friedel-Crafts acylation]]). Acid anhydrides tend to be less [[electrophilic]] than [[acyl chloride]]s, and only one acyl group is transferred per molecule of acid anhydride, which leads to a lower [[atom efficiency]]. The low cost, however, of [[acetic anhydride]] makes it a common choice for [[acetylation]] reactions. Furthermore, the avoidance of chlorocarbons is preferred from the environmental perspective. == Sulfur analogues == [[Sulfur]] can replace oxygen, either in the carbonyl group or in the bridge. In the former case, the name of the acyl group is enclosed in parentheses to avoid ambiguity in the name,<ref name="Blue"/> e.g., (thioacetic) anhydride (CH<sub>3</sub>C(S)OC(S)CH<sub>3</sub>). When two acyl groups are attached to the same sulfur atom, the resulting compound is called a thioanhydride,<ref name="Blue"/> e.g., acetic thioanhydride ((CH<sub>3</sub>C(O))<sub>2</sub>S). == References == <references/> [[Category:Functional groups]] [[Category:Acid anhydrides| ]] [[cs:Anhydridy karboxylových kyselin]] [[de:Säureanhydride]] [[es:Anhídrido de ácido]] [[fr:Anhydride d'acide]] [[ja:カルボン酸無水物]] [[pl:Bezwodniki kwasowe]] [[pt:Anidrido de ácido carboxílico]] [[ru:Ангидриды карбоновых кислот]] [[uk:Ангідриди карбонових кислот]] [[zh:酸酐]]