Acetic anhydride
1406474
226060088
2008-07-16T17:26:29Z
Smokefoot
698909
Re use of Ac2O in Afganistan: rm semi-preachy speculation (probably true) and Wikiepedia self-citation
{{Chembox new
| Name = Acetic anhydride
| ImageFile = Acetic-anhydride-2D-skeletal.png
<!-- | ImageSize = 150px -->
| ImageName = Acetic anhydride
| ImageFile1 = Acetic-anhydride-3D-vdW.png
<!-- | ImageSize1 = 150px -->
| ImageName1 = Acetic anhydride
| IUPACName = Ethanoyl ethanoate
| OtherNames = Acetic anhydride<br />Acetic acid anhydride<br />Acetylacetate<br />Acetyl oxide<br />Acetic oxide<br />Ethanoic anhydride
| Section1 = {{Chembox Identifiers
| SMILES = CC(=O)OC(=O)C
| CASNo = 108-24-7
| RTECS = AK1925000
| InChI=1/C4H6O3/c1-3(5)<br />7-4(2)6/h1-2H3
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>4</sub>H<sub>6</sub>O<sub>3</sub>
| MolarMass = 102.1 g/mol
| Appearance = clear liquid
| Density = 1.08 g/cm³, liquid
| Solubility = 2.6% by weight; rapidly reacts to<br />form [[acetic acid]]
| MeltingPt = −73.1 °C
| BoilingPt = 139.8 °C
}}
| Section3 = {{Chembox Structure
| Dipole =
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| EUClass = Corrosive ('''C''')
| RPhrases = {{R10}}, {{R20/22}}, {{R34}}
| SPhrases = {{S1/2}}, {{S26}}, {{S36/37/39}}, {{S45}}
| FlashPt = 54 °C
}}
| Section8 = {{Chembox Related
| Function = [[acid anhydride]]s
| OtherFunctn = [[Propionic anhydride]]
| OtherCpds = [[Acetic acid]]<br />[[Acetyl chloride]]
}}
}}
'''Acetic anhydride''' is the [[chemical compound]] with the [[chemical formula|formula]] (CH<sub>3</sub>CO)<sub>2</sub>O. Commonly abbreviated [[Acetyl|Ac]]<sub>2</sub>O,<!-- CAUTION: Ac2O is actually actinium oxide --> it is one of the simplest [[acid anhydride]]s and is a widely used [[reagent]] in [[organic synthesis]]. It is a colorless liquid that smells strongly of [[acetic acid]], which is formed by its reaction with the moisture in the air.
==Production==
Acetic anhydride is produced by [[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>
: CH<sub>3</sub>CO<sub>2</sub>CH<sub>3</sub> + CO → (CH<sub>3</sub>CO)<sub>2</sub>O
This process involves the conversion of methyl acetate to [[methyl iodide]] and an acetate salt. Carbonylation of the methyl iodide in turn affords acetyl iodide, which reacts with acetate salts or acetic acid to give the product. Rhodium and lithium iodides are employed as catalysts. Because acetic anhydride is not stable in water, the conversion is conducted under anhydrous conditions. In contrast, the [[Monsanto process|Monsanto acetic acid synthesis]], which also involves a rhodium catalyzed carbonylation of methyl iodide, is at least partially aqueous.
To a decreasing extent, acetic anhydride is also prepared by the reaction of [[ketene]] with acetic acid. Ketene is generated by dehydrating acetic acid at elevated temperatures. This production method was developed by [[Wacker Chemie]] in 1922, when the demand for acetic anhydride increased due to the production of acetic fibre.<!--[http://books.google.com/books?id=36kHHvzx6M8C&pg=PA200&lpg=PA200&dq=wacker+verfahren+essigs%C3%A4ureanhydrid&source=web&ots=n4is04tlMR&sig=NZFcsmFpA1p6p0PBp0zNzAWmFo4#PPA201,M1], [http://www.wacker.com/cms/en/wacker_group/wacker_facts/history/history.jsp]-->
Due to its low cost, acetic anhydride is purchased, not prepared, for use in research laboratories.
==Organic chemistry==
Acetic anhydride is a versatile reagent for [[acetylation]]s, the introduction of acetyl groups to organic substrates. In these conversions, acetic anhydride is viewed as a source of CH<sub>3</sub>CO<sup>+</sup>. [[Alcohol]]s and [[amine]]s are readily acetylated.<ref>{{cite web | title=Science is Fun… | work=Chemical of the Week | url=http://scifun.chem.wisc.edu/CHEMWEEK/AceticAcid/AceticAcid.html | accessdate=2006-03-25}}</ref> For example, the reaction of acetic anhydride with [[ethanol]] is:
: (CH<sub>3</sub>CO)<sub>2</sub>O + CH<sub>3</sub>CH<sub>2</sub>OH → [[ethyl acetate|CH<sub>3</sub>CO<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>]] + CH<sub>3</sub>CO<sub>2</sub>H
Often a base such as [[pyridine]] is added to function as catalyst. In specialized applications, [[Lewis acid]]ic scandium salts have also proven effective catalysts.<ref>Macor, J.; Sampognaro, A. J.; Verhoest, P. R.; Mack, R. A. "(R)-(+)-2-Hydroxy-1,2,2-Triphenylethyl Acetate" Organic Syntheses, Collected Volume 10, p.464 (2004). http://www.orgsyn.org/orgsyn/pdfs/V77P0045.pdf</ref>
Aromatic rings are acetylated, usually in the presence of an acid catalyst. Illustrative is the conversion of benzene to [[acetophenone]]:
: (CH<sub>3</sub>CO)<sub>2</sub>O + C<sub>6</sub>H<sub>6</sub> → CH<sub>3</sub>COC<sub>6</sub>H<sub>5</sub> + CH<sub>3</sub>CO<sub>2</sub>H
===Hydrolysis===
Acetic anhydride dissolves in water to approximately 2.6% by weight.<ref>{{cite web | title=British Petroleum | work=Acetic Anhydride: Frequently Asked Questions (PDF) | url=http://www.bp.com/liveassets/bp_internet/globalbp/STAGING/global_assets/downloads/pdfs/acetyls_aromatics_pta/AceticAnhydrideFAQ.pdf | accessdate=2006-05-03}}</ref> Aqueous solutions have limited stability because, like most acid anhydrides, acetic anhydride hydrolyses to give acetic acid:<ref>{{cite web | title=Celanese | work=Acetic Anhydride: Material Safety Data Sheet (PDF) | url=http://www.celanese.com/msds/pdf/570-22027587.pdf | accessdate=2006-05-03}}</ref>
: (CH<sub>3</sub>CO)<sub>2</sub>O + H<sub>2</sub>O → 2 CH<sub>3</sub>CO<sub>2</sub>H
==Applications==
As indicated by its organic chemistry, Ac<sub>2</sub>O is mainly used for acetylations leading to commercially significant materials. Its largest application is for the conversion of cellulose to [[cellulose acetate]], which is a component of photographic film and other coated materials. Similarly it is used in the production of [[aspirin]], acetyl salicylic acid, which is prepared by the acetylation of [[salicylic acid]]. It is also used as a wood preservative via autoclave impregnation to make a longer lasting timber. Because of its use for the synthesis of [[heroin]] by the diacetylation of [[morphine]], acetic anhydride (known as 'AA' in [[clandestine chemistry]] circles) is listed as a U.S. DEA List II Precursor,<ref>{{cite web | title=ChemGuide | work=Acid Anhydrides | url=http://www.chemguide.co.uk/organicprops/anhydridemenu.html | accessdate=2006-03-25}}</ref> and restricted in many other countries. The largest markets for diverted acetic anhydride continue to be heroin laboratories in Afghanistan.{{fact}}
==Safety==
Acetic anhydride is an irritant and flammable. Because of its reactivity toward water, alcohol foam or carbon dioxide are preferred for fire suppression.<ref>{{cite web | title=Data Sheets | work=International Occupational Safety and Health Information Centre | url=http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc02/icsc0209.htm | accessdate=2006-04-13}}</ref> The vapour of acetic anhydride is harmful.<ref>
{{cite web | title=NIOSH | work=Pocket Guide to Chemical Hazards | url=http://www.cdc.gov/niosh/npg/npgd0003.html | accessdate=2006-04-13}}</ref>
==Notes and references==
<references/>
==See also==
*[[Acid anhydride]]
[[Category:Acid anhydrides]]
[[Category:Lachrymatory agents]]
[[Category:DEA List II chemicals]]
[[da:Eddikesyreanhydrid]]
[[de:Essigsäureanhydrid]]
[[es:Anhídrido acético]]
[[fr:Anhydride acétique]]
[[id:Anhidrida asetat]]
[[it:Anidride acetica]]
[[lv:Acetanhidrīds]]
[[nl:Azijnzuuranhydride]]
[[ja:無水酢酸]]
[[pl:Bezwodnik octowy]]
[[pt:Anidrido acético]]
[[ru:Уксусный ангидрид]]
[[fi:Etikkahappoanhydridi]]
[[sv:Ättiksyraanhydrid]]
[[zh:乙酸酐]]