Editing Acetic anhydride

{{short description|Organic compound with formula (CH₃CO)₂O}}
{{Chembox
| Watchedfields = changed
| verifiedrevid = 477238827
| Name = Acetic anhydride
| ImageFile = Acetic_anhydride2DACS.svg
| ImageClass = skin-invert
| ImageSize = 150px
| ImageName = Acetic anhydride
| ImageFile1 = Acetic-anhydride-from-xtal-2003-3D-balls.png
| ImageClass1 = bg-transparent 
| ImageSize1 = 150px
| ImageName1 = Acetic anhydride
| PIN = Acetic anhydride <!-- Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) -->
| SystematicName = Ethanoic anhydride
| OtherNames = Ethanoyl ethanoate<br />Acetic acid anhydride<br />Acetyl acetate<br />Acetyl oxide<br />Acetic oxide
|Section1={{Chembox Identifiers
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 36610
| SMILES = O=C(OC(=O)C)C
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 2E48G1QI9Q
| InChIKey = WFDIJRYMOXRFFG-UHFFFAOYAH
| SMILES1 = CC(=O)OC(=O)C
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C4H6O3/c1-3(5)7-4(2)6/h1-2H3
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = WFDIJRYMOXRFFG-UHFFFAOYSA-N
| CASNo = 108-24-7
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 7918
| EINECS = 203-564-8
| RTECS = AK1925000
| UNNumber = 1715
| ChEMBL = 1305819
| InChI = 1/C4H6O3/c1-3(5)7-4(2)6/h1-2H3
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 7630
 }}
|Section2={{Chembox Properties
| C=4 | H=6 | O=3
| Appearance = colorless liquid
| Density = 1.082 g cm<sup>−3</sup>, liquid
| Solubility = 2.6 g/100 mL, reacts (''see text'')
| MeltingPtC = −73.1
| BoilingPtC = 139.8
| RefractIndex = 1.3901
| VaporPressure = 4 mmHg (20&nbsp;°C)<ref name=NIOSH/>
| MagSus = −52.8·10<sup>−6</sup> cm<sup>3</sup>/mol
 }}
| Section4 = {{Chembox Thermochemistry
| Thermochemistry_ref = <ref name="crc">{{cite book |author1=John Rumble |title=CRC Handbook of Chemistry and Physics |date=June 18, 2018 |publisher=CRC Press |isbn=978-1138561632 |pages=5–3 |edition=99th |language=en}}</ref>
| HeatCapacity = 
| Entropy =
| DeltaHform = −624.4&nbsp;kJ/mol
| DeltaGfree = 
| DeltaHcombust = 
| DeltaHfus =
| DeltaHvap =
| DeltaHsublim =
| HHV =
| LHV =
 }}
| Section6 = {{Chembox Pharmacology
| Pharmacology_ref = 
| ATCCode_prefix = 
| ATCCode_suffix = 
| ATC_Supplemental = 
| ATCvet = 
| Licence_EU = 
| INN = 
| INN_EMA = 
| Licence_US = 
| Legal_status = 
| Legal_AU = S6
| Legal_AU_comment = 
| Legal_CA = Schedule VI
| Legal_CA_comment = 
| Legal_NZ = 
| Legal_NZ_comment = 
| Legal_UK = 
| Legal_UK_comment = 
| Legal_US = 
| Legal_US_comment = 
| Legal_EU = 
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| Legal_UN = 
| Legal_UN_comment = 
| Pregnancy_category = 
| Pregnancy_AU = 
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| Dependence_liability = 
| AdminRoutes = 
| Bioavail = 
| ProteinBound = 
| Metabolism = 
| Metabolites = 
| OnsetOfAction = 
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| Excretion = 
  }}
|Section7={{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0209.htm ICSC 0209]
| GHSPictograms = {{GHS02}}{{GHS05}}{{GHS07}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|226|302|314|330}}
| PPhrases = {{P-phrases|210|233|240|241|242|243|260|261|264|270|271|280|301+312|301+330+331|303+361+353|304+312|304+340|305+351+338|310|312|321|330|363|370+378|403+235|405|501}}
| NFPA-H = 3
| NFPA-F = 2
| NFPA-R = 1
| NFPA-S = W
| FlashPtC = 49
| AutoignitionPtC = 316
| ExploLimits = 2.7–10.3%
| PEL = TWA 5 ppm (20&nbsp;mg/m<sup>3</sup>)<ref name=NIOSH>{{PGCH|0003}}</ref>
| REL = C 5 ppm (20&nbsp;mg/m<sup>3</sup>)<ref name=NIOSH/>
| IDLH = 200 ppm<ref name=NIOSH/> 
| LC50 = 1000 ppm (rat, 4&nbsp;[[hour|h]])<ref>{{IDLH|108247|Acetic anhydride}}</ref>
 }}
|Section8={{Chembox Related
| OtherFunction_label = [[acid anhydride]]s
| OtherFunction = [[Propionic anhydride]]
| OtherCompounds = [[Acetic acid]]<br />[[Acetyl chloride]]
 }}
}}

'''Acetic anhydride''', or '''ethanoic anhydride''', is the [[chemical compound]] with the [[chemical formula|formula]] {{chem2|(CH3CO)2O}}. Commonly abbreviated {{chem2|[[Acetyl|Ac]]2O}}, it is one the simplest [[organic acid anhydride|anhydride]]s of a [[carboxylic acid]] and is widely used in the production of [[cellulose acetate]] as well as a [[reagent]] in [[organic synthesis]]. It is a colorless liquid that smells strongly of [[acetic acid]], which is formed by its reaction with moisture in the air.

==Structure and properties==
[[File:Acetic anhydride.jpg|thumb|left|Acetic anhydride in a glass bottle]]
Acetic anhydride, like most organic acid anhydrides, is a flexible molecule with a nonplanar structure. The C=O and C-O distances are 1.19 and 1.39 Å.<ref>{{Citation | doi = 10.1107/S2053229616015047 | title = Acetic anhydride at 100 K: the first crystal structure determination | year = 2016 | last1 = Seidel | first1 = R. W. | last2 = Goddard | first2 = R. | last3 = Nöthling | first3 = N. | last4 = Lehmann | first4 = C. W. | journal = Acta Crystallographica Section C | volume = 72 | issue = 10 | pages = 753–757 | pmid = 27703123 | postscript = .}}</ref> The [[Pi bond|pi system linkage]] through the central oxygen offers very weak resonance stabilization compared to the [[dipole|dipole-dipole]] repulsion between the two [[carbonyl]] oxygens. The energy barriers to bond rotation between each of the optimal aplanar conformations are quite low.<ref>{{Citation | doi = 10.1021/jp993131z | title = Acetic Anhydride in the Gas Phase, Studied by Electron Diffraction and Infrared Spectroscopy, Supplemented with ab Initio Calculations of Geometries and Force Fields | year = 2000 | last1 = Wu | first1 = Guang | last2 = Van Alsenoy | first2 = C. | last3 = Geise | first3 = H. J. | last4 = Sluyts | first4 = E. | last5 = Van Der Veken | first5 = B. J. | last6 = Shishkov | first6 = I. F. | last7 = Khristenko | journal = The Journal of Physical Chemistry A | volume = 104 | issue = 7 | pages = 1576–1587 | bibcode = 2000JPCA..104.1576W | postscript = .}}</ref>

==Production==
Acetic anhydride was first synthesized in 1852 by the French chemist [[Charles Frédéric Gerhardt]] (1816-1856) by heating [[potassium acetate]] with [[benzoyl chloride]].<ref>Charles Gerhardt (1852) [https://books.google.com/books?id=MXkbAAAAMAAJ&pg=PA755jV6AQyks “Recherches sur les acides organiques anhydres”] (Investigations into the anhydrides of organic acids), ''Comptes rendus'' … , '''34''' :  755-758.</ref>

Acetic anhydride is produced by [[carbonylation]] of [[methyl acetate]]:<ref>{{citation | last1 = Zoeller | first1 = J. R. | last2 = Agreda | first2 = V. H. | last3 = Cook | first3 = S. L. | last4 = Lafferty | first4 = N. L. | last5 = Polichnowski | first5 = S. W. | last6 = Pond | first6 = D. M. | title = Eastman Chemical Company Acetic Anhydride Process | journal = Catal. Today | year = 1992 | volume = 13 | issue = 1 | pages = 73–91 | doi = 10.1016/0920-5861(92)80188-S}}</ref>
: {{chem2|CH3CO2CH3  +  CO  ->   (CH3CO)2O}}

The [[Monsanto process#Tennessee Eastman acetic anhydride process|Tennessee Eastman acetic anhydride process]] involves the conversion of methyl acetate to [[iodomethane|methyl iodide]]. Carbonylation of the methyl iodide produces [[acetyl iodide]], which reacts with acetate source to give the desired anhydride. [[Rhodium chloride]] in the presence of [[lithium iodide]] is employed as the catalyst. Because acetic anhydride is not stable in water, the conversion is conducted under anhydrous conditions.

To a decreasing extent, acetic anhydride is also prepared by the reaction of ketene ([[ethenone]]) with acetic acid at 45–55&nbsp;°C and low pressure (0.05–0.2&nbsp;bar).<ref name="Arpe">{{citation | last = Arpe | first = Hans-Jürgen | title = Industrielle organische Chemie: Bedeutende vor- und Zwischenprodukte | url = https://books.google.com/books?id=36kHHvzx6M8C&q=wacker+verfahren+essigs%C3%A4ureanhydrid&pg=PA200 | edition = 6th | publisher = Wiley-VCH | location = Weinheim | pages = 200–1 | isbn = 978-3-527-31540-6 | date = 2007-01-11 }}{{Dead link|date=July 2023 |bot=InternetArchiveBot |fix-attempted=yes }}.</ref>
:{{chem2|H2C\dC\dO + CH3COOH   ->   (CH3CO)2O}} 
:(Δ''H'' = −63 kJ/mol)

The route from acetic acid to acetic anhydride via ketene was developed by [[Wacker Chemie]] in 1922,<ref>{{citation | title = Milestones in the history of WACKER | url = http://www.wacker.com/cms/en/wacker_group/wacker_facts/history/history.jsp | publisher = Wacker Chemie AG | access-date = 2009-08-27}}.</ref> when the demand for acetic anhydride increased due to the production of [[cellulose acetate]].

Due to its low cost, acetic anhydride is usually purchased, not prepared, for use in research laboratories.

==Reactions==
Acetic anhydride is a versatile reagent for [[acetylation]]s, the introduction of acetyl groups to organic substrates.<ref>{{citation | title = Acid Anhydrides | url = http://www.chemguide.co.uk/organicprops/anhydridemenu.html | work = Understanding Chemistry | access-date = 2006-03-25}}.</ref> In these conversions, acetic anhydride is viewed as a source of {{chem2|CH3CO+}}.

===Acetylation of alcohols, amines, aromatics===
[[Alcohol (chemistry)|Alcohol]]s and [[amine]]s are readily acetylated.<ref>{{citation | first = Bassam Z. | last = Shakhashiri | title = Acetic Acid & Acetic Anhydride | url = http://scifun.chem.wisc.edu/CHEMWEEK/AceticAcid/AceticAcid.html | work = Science is Fun… | publisher = Department of Chemistry, University of Wisconsin | access-date = 2006-03-25 | archive-url = https://web.archive.org/web/20060303081507/http://scifun.chem.wisc.edu/chemweek/AceticAcid/AceticAcid.html | archive-date = 2006-03-03 | url-status = dead }}.</ref> For example, the reaction of acetic anhydride with [[ethanol]] yields [[ethyl acetate]]:
:{{chem2|(CH3CO)2O + CH3CH2OH -> CH3CO2CH2CH3 + CH3COOH}}
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>{{OrgSynth | last1 = Macor | first1 = John | last2 = Sampognaro | first2 = Anthony J. | last3 = Verhoest | first3 = Patrick R. | last4 = Mack | first4 = Robert A. | title = (''R'')-(+)-2-Hydroxy-1,2,2-Triphenylethyl Acetate | prep = V77P0045 | year = 2000 | volume = 77 | pages = 45 | collvol = 10 | collvolpages = 464 | doi = 10.15227/orgsyn.077.0045 }}</ref>

Aromatic rings are acetylated by acetic anhydride.  Usually acid catalysts are used to accelerate the reaction. Illustrative are the conversions of [[benzene]] to [[acetophenone]]<ref>Roger Adams and C. R. Noller "p-Bromoacetophenone" Org. Synth. 1925, vol. 5, p. 17. {{doi|10.15227/orgsyn.005.0017}}</ref> and [[ferrocene]] to acetylferrocene:<ref>{{citation | last = Taber | first = Douglass F. | title = Column chromatography: Preparation of Acetyl Ferrocene | url = http://valhalla.chem.udel.edu/ferroc.html | publisher = Department of Chemistry and Biochemistry, University of Delaware | access-date = 2009-08-27 | archive-url = https://web.archive.org/web/20090502011406/http://valhalla.chem.udel.edu/ferroc.html | archive-date = 2009-05-02 | url-status = dead }}.</ref>
:{{chem2|(C5H5)2Fe  +  (CH3CO)2O   ->   (C5H5)Fe(C5H4COCH3)  +  CH3CO2H}}

===Preparation of other acid anhydrides===
Dicarboxylic acids are converted to the anhydrides upon treatment with acetic anhydride.<ref>B. H. Nicolet and J. A. Bender "3-Nitrophthalic Anhydride" Org. Synth. 1927, vol. 7, 74.
{{doi|10.15227/orgsyn.007.0074}}</ref>  It is also used for the preparation of mixed anhydrides such as that with nitric acid, [[acetyl nitrate]].

===Precursor to geminal diacetates===
[[Aldehyde]]s react with acetic anhydride in the presence of an acidic [[catalyst]] to give geminal diacetates.<ref>R. T. Bertz "Furfuryl Diacetate" Org. Synth. 1953, 33, 39. {{doi|10.15227/orgsyn.033.0039}}</ref>  A former industrial route to [[vinyl acetate]] involved the intermediate [[ethylidene diacetate]], the geminal diacetate obtained from [[acetaldehyde]] and acetic anhydride:<ref>G. Roscher "Vinyl Esters" in ''Ullmann's Encyclopedia of Chemical Technology'', 2007 John Wiley & Sons: New York. {{doi|10.1002/14356007.a27_419}}</ref>
:{{chem2|CH3CHO  +  (CH3CO)2O   ->   (CH3CO2)2CHCH3}}

===Hydrolysis===
Acetic anhydride dissolves in water to approximately 2.6% by weight.<ref>{{citation|title=Acetic Anhydride: Frequently Asked Questions |url=http://www.bp.com/liveassets/bp_internet/globalbp/STAGING/global_assets/downloads/pdfs/acetyls_aromatics_pta/AceticAnhydrideFAQ.pdf |publisher=British Petroleum |access-date=2006-05-03 |url-status=dead |archive-url=https://web.archive.org/web/20071011104749/http://www.bp.com/liveassets/bp_internet/globalbp/STAGING/global_assets/downloads/pdfs/acetyls_aromatics_pta/AceticAnhydrideFAQ.pdf |archive-date=2007-10-11 }}.</ref> Aqueous solutions have limited stability because, like most acid anhydrides, acetic anhydride hydrolyses to give carboxylic acids. In this case, acetic acid is formed, this reaction product being fully water miscible:<ref>{{citation|title=Acetic Anhydride: Material Safety Data Sheet (PDF) |url=http://www.celanese.com/msds/pdf/570-22027587.pdf |publisher=Celanese |access-date=2006-05-03 |url-status=dead |archive-url=https://web.archive.org/web/20070927025258/http://www.celanese.com/msds/pdf/570-22027587.pdf |archive-date=2007-09-27 }}.</ref>
:{{chem2|(CH3CO)2O + H2O -> 2 CH3COOH}}

===Enolate formation===
Acetic anhydride forms the enolate in the presence of [[acetate]] as base.  The enolate can be [[chemical trap|trapped]] by condenation with [[benzaldehyde]].  In the 19th century, this chemistry,  the [[Perkin reaction]], was used for the production of [[cinnamic acid]]:<ref>{{Cite book |last=Lassar-Cohn |first=Dr |url=https://books.google.com/books?id=KxhIAAAAIAAJ&pg=PA104 |title=A Laboratory Manual of Organic Chemistry: A Compendium of Laboratory Methods for the Use of Chemists, Physicians, and Pharmacists |last2=Smith |first2=Alexander |date=1895 |publisher=Macmillian and Company Limited |language=en}}</ref>
:{{chem2|(CH3CO)2O  +  C6H5CHO  ->  C6H5CH\dCHCO2H  +  CH3CO2H}}

===Lewis base properties===
The carbonyl groups in acetic anhydride are weakly basic.  A number of adducts are known, such as the derivative of [[titanium tetrachloride]], TiCl<sub>4</sub>((CH<sub>3</sub>CO)<sub>2</sub>O).<ref>{{cite journal|author=B. Viard, M. Poulain, D. Grandjean, J. Amaudrut|journal=J. Chem. Res.|volume=84|year=1983|page=853}}</ref> 

==Applications==
As indicated by its organic chemistry, acetic anhydride 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, and is used in the manufacture of cigarette filters. Similarly it is used in the production of [[aspirin]] (acetylsalicylic acid), which is prepared by the acetylation of [[salicylic acid]].<ref name="SIDS">{{SIDS-ref|name=Acetic anhydride|id=108247|page=5}}{{Dead link|date=January 2024}}</ref> It is also used as an active modification agent via [[autoclave]] impregnation and subsequent acetylation to make a durable and long-lasting timber.<ref>{{cite news |last1=Tullo | first1=Alexander |title=Making Wood Last Forever With Acetylation |url=https://cen.acs.org/articles/90/i32/Making-Wood-Last-Forever-Acetylation.html |access-date=2022-09-17 |work=Chemical and Engineering News |issue=32 |publisher=American Chemical Society|date=2012-08-06 |issn=0009-2347 }}</ref>

Acetic anhydride is commonly used for the production of [[modified starch]]es (E1414, E1420, E1422).

== Legal status ==
Because of its use for the synthesis of [[heroin]] by the diacetylation of [[morphine]], acetic anhydride is listed as a U.S. DEA List II precursor and is restricted in many other countries.<ref>{{Cite web|date=2022-02-15|title=§ 1310.02 - Substances Covered|url=https://www.ecfr.gov/current/title-21/chapter-II/part-1310/section-1310.02|url-status=live|archive-url=https://web.archive.org/web/20220215120955/https://www.ecfr.gov/current/title-21/chapter-II/part-1310/section-1310.02|archive-date=2022-02-15|website=[[e-CFR]]}}</ref><ref>{{citation | title = UN Intercepts Taliban's Heroin Chemical in Rare Afghan Victory | url = https://www.bloomberg.com/apps/news?pid=20670001&refer=home&sid=aY1eg_RtBNNU | publisher = [[Bloomberg L.P.|Bloomberg]] | access-date = 2008-10-07 |archive-url=https://web.archive.org/web/20121022213218/http://www.bloomberg.com/apps/news?pid=newsarchive&refer=home&sid=aY1eg_RtBNNU |archive-date=22 October 2012|url-status=dead}}.</ref>

==Safety==
Acetic anhydride is an irritant and combustible liquid; it is highly corrosive to skin and any direct contact will result in burns. Because of its reactivity toward water and 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.inchem.org/documents/icsc/icsc/eics0209.htm | access-date=2006-04-13}}</ref> The vapour of acetic anhydride is harmful.<ref>
{{cite web | title=NIOSH | work=Pocket Guide to Chemical Hazards | url=https://www.cdc.gov/niosh/npg/npgd0003.html | access-date=2006-04-13| archive-url= https://web.archive.org/web/20060422144317/http://www.cdc.gov/niosh/npg/npgd0003.html| archive-date= 22 April 2006 | url-status= live}}</ref>

==References==
{{reflist}}

==External links==
*[http://www.inchem.org/documents/icsc/icsc/eics0209.htm ICSC 0209]
*[https://www.cdc.gov/niosh/npg/npgd0003.html NIOSH Pocket Guide to Chemical Hazards]

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{{DEFAULTSORT:Acetic Anhydride}}
[[Category:Carboxylic anhydrides]]
[[Category:Lachrymatory agents]]
[[Category:Solvents]]
[[Category:Acetylating agents]]
[[Category:Acetyl compounds]]