View source for Acetic acid

{{Short description|Chemical acid found in vinegar}}
{{Redirect-distinguish|Acetic|Asceticism{{!}}Ascetic}}
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{{Use dmy dates|date=July 2019}}
{{Use Oxford spelling|date=September 2016}}
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{{Chembox
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| Watchedfields = changed
| verifiedrevid = 477238786
| Name = 
| ImageFile = 
| ImageFileL1 = Acetic-acid-2D-skeletal.svg
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageClassL1 = skin-invert
| ImageNameL1 = Skeletal formula of acetic acid
| ImageFileR1 = Acetic-acid-CRC-GED-3D-vdW-B.png
| ImageClassR1 = bg-transparent 
| ImageFileR1_Ref = {{chemboximage|correct|??}}
| ImageNameR1 = Spacefill model of acetic acid
| ImageFileL2 = Essigsäure - Acetic acid.svg
| ImageFileL2_Ref = {{chemboximage|correct|??}}
| ImageClassL2 = skin-invert
| ImageNameL2 = Skeletal formula of acetic acid with all explicit hydrogens added
| ImageFileR2 = Acetic-acid-CRC-GED-3D-balls-B.png
| ImageClassR2 = bg-transparent 
| ImageFileR2_Ref = {{chemboximage|correct|??}}
| ImageNameR2 = Ball and stick model of acetic acid
| ImageFile3 = Acetic acid.jpg
| ImageFile3_Ref = {{chemboximage|correct|??}}
| ImageSize3 = 244
| ImageName3 = Sample of acetic acid in a reagent bottle
| PIN = Acetic acid<ref name=iupac2013>{{cite book | title =  Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = The [[Royal Society of Chemistry]] | date = 2014 | location = Cambridge | page = 745 | doi = 10.1039/9781849733069-00648 | isbn = 978-0-85404-182-4}}</ref>
| SystematicName = Ethanoic acid
| OtherNames = Vinegar (when dilute); Hydrogen acetate; Methanecarboxylic acid; Ethylic acid<ref>{{cite book |title=Scientific literature reviews on generally recognised as safe (GRAS) food ingredients |publisher=National Technical Information Service |year=1974 |page=1}}</ref><ref>"Chemistry", volume 5, Encyclopædia Britannica, 1961, page 374.</ref>
| IUPACName = 
| Section1 = {{Chembox Identifiers
| Abbreviations = AcOH
| CASNo = 64-19-7
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 176
| ChemSpiderID = 171
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| UNII = Q40Q9N063P
| UNII_Ref = {{fdacite|correct|FDA}}
| EINECS = 200-580-7 
| UNNumber = 2789
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank = DB03166
| KEGG = C00033
| KEGG1 = D00010
| KEGG1_Ref = {{keggcite|correct|kegg}}
| MeSHName = Acetic+acid
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 15366
| ChEMBL = 539
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| IUPHAR_ligand = 1058
| Beilstein = 506007
| Gmelin = 1380
| 3DMet = B00009
| RTECS = AF1225000
| SMILES = CC(O)=O
| StdInChI = 1S/C2H4O2/c1-2(3)4/h1H3,(H,3,4)
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = QTBSBXVTEAMEQO-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
}}
| Section2 = {{Chembox Properties
| Formula = {{chem2|CH3COOH}}
| C=2|H=4|O=2
| Appearance = Colourless liquid
| Odor = Heavily vinegar-like

| Density = 1.049 g/cm<sup>3</sup> (liquid); 1.27 g/cm<sup>3</sup> (solid)
| Solubility = [[Miscibility|Miscible]]
| MeltingPtK = 289 to 290
| BoilingPtK = 391 to 392
| pKa = 4.756
| ConjugateBase = [[Acetate]]
| Viscosity = 1.22 mPa s <br /> 1.22 cP
| RefractIndex = 1.371 (V<sub>D</sub> = 18.19)
| Dipole = 1.74 D
| MagSus = −31.54·10<sup>−6</sup> cm<sup>3</sup>/mol
| LogP = −0.28<ref name="chemsrc">{{Cite web|url=https://www.chemsrc.com/en/cas/64-19-7_162032.html|title=acetic acid|website=www.chemsrc.com}}</ref>
| VaporPressure = 1.54653947{{nbsp}}kPa (20&nbsp;°C) <br /> 11.6{{nbsp}}mmHg (20&nbsp;°C)<ref name="lange">''Lange's Handbook of Chemistry'', 10th ed.</ref>
}}
| Section3 = 
| Section4 = 
| Section5 = {{Chembox Thermochemistry
| DeltaHf = −483.88–483.16 kJ/mol
| DeltaHc = −875.50–874.82 kJ/mol
| Entropy = 158.0 J/(K⋅mol)
| HeatCapacity = 123.1 J/(K⋅mol)
}}
| Section6 = {{Chembox Pharmacology
| Pharmacology_ref = 
| ATCCode_prefix = G01
| ATCCode_suffix = AD02
| ATC_Supplemental = {{ATC|S02|AA10}}
| ATCvet = 
| Licence_EU = 
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| INN_EMA = 
| Licence_US = 
| Legal_status = 
| Legal_AU = S2
| Legal_AU_comment = and S6
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| Dependence_liability = 
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| Bioavail = 
| ProteinBound = 
| Metabolism = 
| Metabolites = 
| OnsetOfAction = 
| HalfLife = 
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| Excretion = 
}}
| Section7 = {{Chembox Hazards
| GHSPictograms = {{GHS02}} {{GHS05}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|226|314}}
| PPhrases = {{P-phrases|280|305+351+338|310}}
| NFPA-F = 2
| NFPA-H = 3
| NFPA-R = 0
| FlashPtC = 40
| AutoignitionPtC = 427
| LD50 = 3.31 g/kg, oral (rat)
| LC50 = 5620 ppm (mouse, 1 [[hour|h]])<br />16000 ppm (rat, 4&nbsp;h)<ref>{{IDLH|64197|Acetic acid}}</ref>
| ExploLimits = 4–16%
| PEL = TWA 10 ppm (25&nbsp;mg/m<sup>3</sup>)<ref name=PGCH>{{PGCH|0002}}</ref>
| REL = TWA 10 ppm (25&nbsp;mg/m<sup>3</sup>) ST&nbsp;15&nbsp;ppm (37&nbsp;mg/m<sup>3</sup>)<ref name=PGCH />
| IDLH = 50 ppm<ref name=PGCH />
}}
| Section8 = {{Chembox Related
| OtherFunction_label = [[carboxylic acid]]s
| OtherFunction = [[Formic acid]]<br />[[Propionic acid]]
| OtherCompounds = [[Acetaldehyde]]<br />[[Acetamide]]<br />[[Acetic anhydride]]<br />[[Chloroacetic acid]]<br />[[Acetyl chloride]]<br />[[Glycolic acid]]<br />[[Ethyl acetate]]<br />[[Potassium acetate]]<br />[[Sodium acetate]]<br />[[Thioacetic acid]]
}}
}}
{{Infobox drug
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| Drugs.com = {{drugs.com|monograph|acetic-acid}}
}}

'''Acetic acid''' {{IPAc-en|ə|ˈ|s|iː|t|ᵻ|k}}, systematically named '''ethanoic acid''' {{IPAc-en|ˌ|ɛ|θ|ə|ˈ|n|oʊ|ᵻ|k}}, is an acidic, colourless liquid and [[organic compound]] with the [[chemical formula]] {{chem2|CH3COOH}} (also written as {{chem2|CH3CO2H}}, {{chem2|C2H4O2}}, or {{chem2|HC2H3O2}}). [[Vinegar]] is at least 4% acetic acid by volume, making acetic acid the main component of vinegar apart from water. Historically, vinegar was produced from the third century BC and was likely the first acid to be produced in large quantities.

Acetic acid is the second simplest [[carboxylic acid]] (after [[formic acid]]). It is an important [[Reagent|chemical reagent]] and industrial chemical across various fields, used primarily in the production of [[cellulose acetate]] for [[photographic film]], [[polyvinyl acetate]] for wood [[Adhesive|glue]], and [[synthetic fibres]] and fabrics. In households, diluted acetic acid is often used in [[descaling agent]]s. In the [[food industry]], acetic acid is controlled by the [[E number|food additive code]] E260 as an [[acidity regulator]] and as a condiment. In [[biochemistry]], the [[acetyl group]], derived from acetic acid, is fundamental to all forms of life. When bound to [[coenzyme A]], it is central to the [[metabolism]] of [[carbohydrate]]s and [[fat]]s.

The global demand for acetic acid as of 2023 is about 17.88 million [[Tonne|metric tonnes]] per year (t/a). Most of the world's acetic acid is produced via the [[carbonylation]] of [[methanol]]. Its production and subsequent industrial use poses health hazards to workers, including incidental skin damage and chronic respiratory injuries from inhalation.

== Nomenclature ==

The [[trivial name]] "acetic acid" is the most commonly used and [[preferred IUPAC name]]. The systematic name "ethanoic acid", a valid [[IUPAC]] name, is constructed according to the substitutive nomenclature.<ref name="BB-prs310305">IUPAC Provisional Recommendations 2004 [http://old.iupac.org/reports/provisional/abstract04/BB-prs310305/Chapter1.pdf Chapter P-12.1; page 4]</ref> The name "acetic acid" derives from the [[Latin]] word for [[vinegar]], "{{wikt-lang|la|acetum}}", which means "to sour" in relation to the bitter taste of fermented fruits.<ref name="Myers" />

"Glacial acetic acid" is a name for water-free ([[anhydrous]]) acetic acid. Similar to the [[German language|German]] name "Eisessig" ("ice vinegar"), the name comes from the solid ice-like crystals that form with agitation, slightly below room temperature at {{convert|16.6|C|F}}. Acetic acid can never be truly water-free in an atmosphere that contains water, so the presence of 0.1% water in glacial acetic acid lowers its melting point by 0.2&nbsp;°C.<ref name="Purification of Laboratory Chemicals">{{cite book| vauthors = Armarego WL, Chai C |title=Purification of Laboratory Chemicals | edition = 6th |publisher=Butterworth-Heinemann|year=2009|isbn=978-1-85617-567-8}}</ref>

A common [[symbol (chemistry)|symbol]] for acetic acid is AcOH (or HOAc), where Ac is the [[pseudoelement symbol]] representing the [[acetyl]] [[functional group|group]] {{chem2|CH3\sC(\dO)\s}}; the [[conjugate acid|conjugate base]], [[acetate]] ({{chem2|CH3COO−}}), is thus represented as {{chem2|AcO−}}.<ref name="Cooper">{{cite book| vauthors = Cooper C |title=Organic Chemist's Desk Reference|edition=2nd |date=9 August 2010|publisher=CRC Press|isbn=978-1-4398-1166-5|pages=102–104}}</ref> Acetate is the [[ion]] resulting from loss of {{chem2|[[proton|H+]]}} from acetic acid. The name "acetate" can also refer to a [[salt (chemistry)|salt]] containing this anion, or an [[ester]] of acetic acid.<ref>{{cite book| vauthors = Hendrickson JB, Cram DJ, Hammond GS |title=Organic Chemistry|edition=3rd|year=1970|publisher=McGraw Hill Kogakusha|location=Tokyo|page=135}}</ref> (The symbol Ac for the acetyl functional group is not to be confused with the symbol Ac for the element [[actinium]]; context prevents confusion among organic chemists). To better reflect its structure, acetic acid is often written as {{chem2|CH3\sC(O)OH}}, {{chem2|CH3\sC(\dO)\sOH}}, {{chem2|CH3COOH}}, and {{chem2|CH3CO2H}}. In the context of [[acid–base reaction]]s, the abbreviation HAc is sometimes used,<ref>{{cite book| vauthors = DeSousa LR |title=Common Medical Abbreviations|year=1995|publisher=Cengage Learning|isbn=978-0-8273-6643-5|page=[https://archive.org/details/commonmedicalabb0000unse/page/97 97]|url=https://archive.org/details/commonmedicalabb0000unse/page/97}}</ref> where Ac in this case is a symbol for acetate (rather than acetyl).

The carboxymethyl functional group derived from removing one hydrogen from the [[methyl]] group of acetic acid has the [[chemical formula]] {{chem2|\sCH2\sC(\dO)\sOH}}.

== History ==
[[Vinegar]] is a diluted solution of acetic acid and was known early in civilization as the natural result of exposure of [[beer]] and [[wine]] to air because acetic acid-producing bacteria are present globally. It is likely the first acid to be produced in large quantities in history.<ref name="Myers">{{cite book |last1=Myers |first1=Richard Leroy |title=The 100 Most Important Chemical Compounds: A Reference Guide |date=2007 |publisher=Greenwood Press |isbn=9780313337581 |page=1-3}}</ref> The use of acetic acid in [[alchemy]] extends into the third century BC, when the Greek philosopher [[Theophrastus]] described how vinegar acted on metals to produce [[pigment]]s useful in art, including ''white lead'' ([[lead carbonate]]) and ''[[verdigris]]'', a green mixture of [[copper]] salts including [[copper(II) acetate]]. Hippocrates used vinegar as an antiseptic and as a remedy for numerous conditions including fever, constipation, ulcers, and pleurisy.<ref name="Myers" /> Ancient [[Rome|Romans]] boiled soured wine to produce a highly sweet syrup called ''sapa''. [[Defrutum|Sapa]] that was produced in lead pots was rich in [[Lead(II) acetate|lead acetate]], a sweet substance also called ''sugar of lead'' or ''sugar of [[Saturn (mythology)|Saturn]]'', which contributed to [[lead poisoning]] among the Roman aristocracy.<ref name="martin">{{cite book | vauthors = Martin G |url=https://archive.org/details/dli.bengal.10689.10857 |title=Industrial and Manufacturing Chemistry |publisher=Crosby Lockwood |year=1917 |edition=Part 1, Organic |location=London |pages=[https://archive.org/details/dli.bengal.10689.10857/page/n348 330]–331}}</ref>

In the 16th-century [[Germany|German]] alchemist [[Andreas Libavius]] described the production of [[acetone]] from the [[dry distillation]] of lead acetate, [[ketonic decarboxylation]]. The presence of water in vinegar has such a profound effect on acetic acid's properties that for centuries chemists believed that glacial acetic acid and the acid found in vinegar were two different substances. French chemist [[Pierre Adet]] proved them identical.<ref name="martin" /><ref>{{cite journal | vauthors = Adet PA |year=1798 |title=Mémoire sur l'acide acétique | trans-title = Memoir on acetic acid | language = French |journal=Annales de Chimie |volume=27 |pages=299–319}}</ref>
[[File:AceticAcid012.jpg|upright|thumb|alt=glass beaker of crystallized acetic acid|Crystallized acetic acid]]
In 1845 German chemist [[Hermann Kolbe]] [[Chemical synthesis|synthesized]] acetic acid from [[inorganic compound]]s for the first time. This reaction sequence consisted of [[chlorination reaction|chlorination]] of [[carbon disulfide]] to [[carbon tetrachloride]], followed by [[pyrolysis]] to [[tetrachloroethylene]] and aqueous chlorination to [[trichloroacetic acid]], and concluded with [[electrolysis|electrolytic]] [[organic redox reaction|reduction]] to acetic acid.<ref name="goldwhite">{{cite journal | vauthors = Goldwhite H |date=September 2003 |title=This month in chemical history |url=http://membership.acs.org/N/NewHaven/bulletins/Bulletin_2003-09.pdf |url-status=dead |journal=New Haven Section Bulletin American Chemical Society |volume=20 |issue=3 |page=4 |archive-url=https://web.archive.org/web/20090304210839/http://membership.acs.org/N/NewHaven/bulletins/Bulletin_2003-09.pdf |archive-date=4 March 2009}}</ref>

By 1910, most glacial acetic acid was obtained from the [[pyroligneous acid|pyroligneous liquor]], a product of the distillation of wood. The acetic acid was isolated by treatment with [[limewater|milk of lime]], and the resulting [[calcium acetate]] was then acidified with [[sulfuric acid]] to recover acetic acid. At that time, Germany was producing 10,000 [[ton]]s of glacial acetic acid, around 30% of which was used for the manufacture of [[indigo dye]].<ref name="martin" /><ref name="schweppe">{{cite journal | vauthors = Schweppe H |year=1979 |title=Identification of dyes on old textiles |url=http://aic.stanford.edu/jaic/articles/jaic19-01-003_1.html |url-status=dead |journal=Journal of the American Institute for Conservation |volume=19 |issue=1/3 |pages=14–23 |doi=10.2307/3179569 |jstor=3179569 |archive-url=https://web.archive.org/web/20090529021302/http://aic.stanford.edu/jaic/articles/jaic19-01-003_1.html |archive-date=29 May 2009 |access-date=12 October 2005|url-access=subscription }}</ref>

Because both [[methanol]] and [[carbon monoxide]] are commodity raw materials, methanol carbonylation long appeared to be attractive precursors to acetic acid. [[Henri Dreyfus]] at [[British Celanese]] developed a methanol carbonylation pilot plant as early as 1925.<ref name="wagner">{{cite book | vauthors = Wagner FS |title=Kirk-Othmer Encyclopedia of Chemical Technology |publisher=[[John Wiley & Sons]] |year=1978 | veditors = Grayson M |edition=3rd |location=New York |chapter=Acetic acid}}</ref> However, a lack of practical materials that could contain the corrosive reaction mixture at the high [[pressure]]s needed (200 [[Atmosphere (unit)|atm]] or more) discouraged commercialization of these routes. The first commercial methanol carbonylation process, which used a [[cobalt]] catalyst, was developed by German chemical company [[BASF]] in 1963. In 1968, a [[rhodium]]-based catalyst (''cis''−{{chem2|[Rh(CO)2I2]−}}) was discovered that could operate efficiently at lower pressure with almost no by-products. US chemical company [[Monsanto Company]] built the first plant using this catalyst in 1970, and rhodium-catalyzed methanol carbonylation became the dominant method of acetic acid production (see [[Monsanto process]]). In the late 1990s, [[BP]] Chemicals commercialized the Cativa catalyst ({{chem2|[Ir(CO)2I2]−}}), which is promoted by [[iridium]] for greater efficiency.<ref>[https://books.google.com/books?id=4KHzc-nYPNsC&dq=Cativa+BP&pg=PA365 Industrial Organic Chemicals], Harold A. Wittcoff, Bryan G. Reuben, Jeffery S. Plotkin</ref> Known as the [[Cativa process]], the [[iridium]]-catalyzed production of glacial acetic acid is [[Green chemistry|greener]], and has largely supplanted the Monsanto process, often in the same production plants.<ref name="lancaster">{{cite book | vauthors = Lancaster M |url= https://archive.org/details/greenchemistryin00lanc/page/262 |title=Green Chemistry, an Introductory Text |publisher=Royal Society of Chemistry |year=2002 |isbn=978-0-85404-620-1 |location=Cambridge |pages=[https://archive.org/details/greenchemistryin00lanc/page/262 262–266] |url-access=registration}}</ref>

=== Interstellar medium ===
[[Interstellar medium|Interstellar]] acetic acid was discovered in 1996 by a team led by David Mehringer<ref name="Meh">{{cite journal | vauthors = Mehringer DM, Snyder LE, Miao Y, Lovas FJ |year=1997 |title=Detection and Confirmation of Interstellar Acetic Acid |journal=Astrophysical Journal Letters |volume=480 |issue=1 |page=L71 |bibcode=1997ApJ...480L..71M |doi=10.1086/310612 |doi-access=free}}</ref> using the former [[Berkeley-Illinois-Maryland Association]] array at the [[Hat Creek Radio Observatory]] and the former [[Millimeter Array]] located at the [[Owens Valley Radio Observatory]]. It was first detected in the [[Sagittarius B2]] North molecular cloud (also known as the Sgr B2 [[Large Molecule Heimat]] source). Acetic acid has the distinction of being the first molecule discovered in the interstellar medium using solely [[Radio telescope#Radio interferometry|radio interferometers]]; in all previous ISM molecular discoveries made in the millimetre and centimetre wavelength regimes, single dish radio telescopes were at least partly responsible for the detections.<ref name="Meh" />

== Properties ==
[[File:AceticAcid010.png|thumb|upright|Acetic acid crystals]]

=== Acidity ===
The hydrogen centre in the [[carboxyl group]] (−COOH) in carboxylic acids such as acetic acid can separate from the molecule by ionization:
:{{chem2|CH3COOH ⇌ CH3CO2− + H+}}
Because of this release of the [[proton]] ({{chem2|H+}}), acetic acid has acidic character. Acetic acid is a weak [[monoprotic acid]]. In aqueous solution, it has a [[Acid dissociation constant|pK<sub>a</sub>]] value of 4.76.<ref name="Goldmine">{{cite journal |title=Thermodynamic Quantities for the Ionization Reactions of Buffers | vauthors = Goldberg R, Kishore N, Lennen R |journal=Journal of Physical and Chemical Reference Data |volume=31 |issue=2|pages=231–370 |year=2002 |url=https://www.nist.gov/data/PDFfiles/jpcrd615.pdf |archive-url=https://web.archive.org/web/20081006062140/https://www.nist.gov/data/PDFfiles/jpcrd615.pdf |url-status=dead |archive-date=6 October 2008 |doi=10.1063/1.1416902|bibcode = 2002JPCRD..31..231G}}</ref> Its [[conjugate acid|conjugate base]] is [[acetate]] ({{chem2|CH3COO−}}). A 1.0&nbsp;[[Molarity|M]] solution (about the concentration of domestic vinegar) has a [[pH]] of 2.4, indicating that merely 0.4% of the acetic acid molecules are dissociated.{{efn|1=[H<sub>3</sub>O<sup>+</sup>] = 10<sup>−2.4</sup> = 0.4%}}

[[File:Acetic acid deprotonation.svg|class=skin-invert-image|375px|Deprotonation equilibrium of acetic acid in water]]
[[File:Acetic Acid Hydrogenbridge V.1.svg|class=skin-invert-image|thumb|Cyclic dimer of acetic acid; dashed <span style="color:green;">'''green'''</span> lines represent hydrogen bonds]]

=== Structure ===
In solid acetic acid, the molecules form chains of individual molecules interconnected by [[hydrogen bond]]s.<ref name="jones">{{cite journal| vauthors = Jones RE, Templeton DH |year = 1958|title = The crystal structure of acetic acid|journal = Acta Crystallographica|volume = 11|issue = 7|pages=484–487|doi = 10.1107/S0365110X58001341|hdl = 2027/mdp.39015077597907 |url = https://cloudfront.escholarship.org/dist/prd/content/qt3x45b5nd/qt3x45b5nd.pdf|doi-access = free|bibcode = 1958AcCry..11..484J }}</ref> In the vapour phase at {{convert|120|C|F}}, [[Dimer (chemistry)|dimers]] can be detected. Dimers also occur in the liquid phase in dilute solutions with non-hydrogen-bonding solvents, and to a certain extent in pure acetic acid,<ref name="briggs">{{cite journal| vauthors = Briggs JM, Nguyen TB, Jorgensen WL |title = Monte Carlo simulations of liquid acetic acid and methyl acetate with the OPLS potential functions|journal = Journal of Physical Chemistry|year = 1991|volume = 95|pages=3315–3322|doi = 10.1021/j100161a065|issue = 8}}</ref> but are disrupted by hydrogen-bonding solvents. The dissociation [[enthalpy]] of the dimer is estimated at 65.0–66.0&nbsp;kJ/mol, and the dissociation entropy at 154–157&nbsp;J&nbsp;mol<sup>−1</sup>&nbsp;K<sup>−1</sup>.<ref name="togeas">{{cite journal | vauthors = Togeas JB | title = Acetic acid vapor: 2. A statistical mechanical critique of vapor density experiments | journal = The Journal of Physical Chemistry A | volume = 109 | issue = 24 | pages = 5438–5444 | date = June 2005 | pmid = 16839071 | doi = 10.1021/jp058004j | bibcode = 2005JPCA..109.5438T }}</ref> Other carboxylic acids engage in similar intermolecular hydrogen bonding interactions.<ref>{{cite book| vauthors = McMurry J |title=Organic Chemistry|url=https://archive.org/details/organicchemistry00youn|url-access=registration|edition=5th|year=2000|publisher=Brooks/Cole|isbn=978-0-534-37366-5|page=818}}</ref>

=== Solvent properties ===
[[Liquid]] acetic acid is a [[hydrophile|hydrophilic]] ([[Polar molecule|polar]]) [[protic solvent]], similar to [[ethanol]] and [[water]]. With a [[relative static permittivity]] (dielectric constant) of 6.2, it dissolves not only polar compounds such as inorganic salts and [[sugar]]s, but also non-polar compounds such as oils as well as polar solutes. It is miscible with polar and non-polar [[solvent]]s such as water, [[chloroform]], and [[hexane]]. With higher alkanes (starting with [[octane]]), acetic acid is not [[miscible]] at all compositions, and solubility of acetic acid in alkanes declines with longer n-alkanes.<ref name="Zieborak">{{cite journal | vauthors = Zieborak K, Olszewski K |title=Solubility of n-paraffins in acetic acid |journal = Bulletin de l'Académie Polonaise des Sciences, Série des Sciences Chimiques, Géologiques et Géographiques |year = 1958|volume = 6|issue=2|pages=3315–3322}}</ref> The solvent and [[miscibility]] properties of acetic acid make it a useful industrial chemical, for example, as a solvent in the production of [[dimethyl terephthalate]].<ref name=Ullmann>{{Ullmann | vauthors = Le Berre C, Serp P, Kalck, P, Torrence GP | title = Acetic Acid | doi = 10.1002/14356007.a01_045.pub3|year=2013|publisher=Wiley-VCH|location=Weinheim}}</ref>

=== Biochemistry ===
At physiological pHs, acetic acid is usually fully ionized to [[acetate]] in aqueous solution.<ref>{{Cite book |last=Zumdahl |first=Steven S. |url=https://books.google.com/books?id=x6TuAAAAMAAJ |title=Chemistry |date=1986 |publisher=D.C. Heath |isbn=978-0-669-04529-1 |location=Lexington, Mass |pages=627}}</ref>

The [[acetyl]] [[functional group|group]], formally derived from acetic acid, is fundamental to all forms of life. Typically, it is bound to [[coenzyme A]] by [[acetyl-CoA synthetase]] enzymes,<ref>{{cite journal | vauthors = Schwer B, Bunkenborg J, Verdin RO, Andersen JS, Verdin E | title = Reversible lysine acetylation controls the activity of the mitochondrial enzyme acetyl-CoA synthetase 2 | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 27 | pages = 10224–10229 | date = July 2006 | pmid = 16788062 | pmc = 1502439 | doi = 10.1073/pnas.0603968103 | doi-access = free | bibcode = 2006PNAS..10310224S }}</ref> where it is central to the [[metabolism]] of [[carbohydrate]]s and [[fat]]s. Unlike longer-chain carboxylic acids (the [[fatty acids]]), acetic acid does not occur in natural [[triglyceride]]s. Most of the acetate generated in cells for use in [[acetyl-CoA]] is synthesized directly from [[ethanol]] or [[Pyruvic acid|pyruvate]].<ref>{{cite journal | vauthors = Bose S, Ramesh V, Locasale JW | title = Acetate Metabolism in Physiology, Cancer, and Beyond | journal = Trends in Cell Biology | volume = 29 | issue = 9 | pages = 695–703 | date = September 2019 | pmid = 31160120 | pmc = 6699882 | doi = 10.1016/j.tcb.2019.05.005 }}</ref> However, the artificial triglyceride [[triacetin]] (glycerine triacetate) is a common food additive and is found in cosmetics and topical medicines; this additive is metabolized to [[glycerol]] and acetic acid in the body.<ref>{{cite journal | vauthors = Fiume MZ | title = Final report on the safety assessment of triacetin | journal = International Journal of Toxicology | volume = 22 | issue = Suppl 2 | pages = 1–10 | date = June 2003 | pmid = 14555416 | doi = 10.1080/747398359 }}</ref>

Acetic acid is produced and [[Excretion|excreted]] by [[acetic acid bacteria]], notably the genus ''[[Acetobacter]]'' and ''[[Clostridium acetobutylicum]]''. These bacteria are found universally in [[food]]stuffs, [[water]], and [[soil]], and acetic acid is produced naturally as fruits and other foods spoil. Acetic acid is also a component of the [[vaginal lubrication]] of [[human]]s and other [[primate]]s, where it appears to serve as a mild [[antibacterial]] agent.<ref name="dict">{{cite book|title = Dictionary of Organic Compounds|edition = 6th|volume = 1 |year = 1996|location = London|publisher = Chapman & Hall|isbn = 978-0-412-54090-5| veditors = Buckingham J }}</ref>

== Production ==
[[File:Acetic acid 1884 plant.jpg|thumb|Purification and concentration plant for acetic acid in 1884]]
Acetic acid is produced industrially both naturally via bacterial [[fermentation (biochemistry)|fermentation]] and synthetically.<ref name="Myers" /> About 75% of acetic acid made for use in the chemical industry is made by the [[carbonylation]] of [[methanol]], explained below.<ref name=Ullmann /> The biological route accounts for only about 10% of world production, but it remains important for the production of vinegar because many food purity laws require vinegar used in foods to be of biological origin. Other processes are [[methyl formate]] isomerization, conversion of [[syngas]] to acetic acid, and gas phase oxidation of [[ethylene]] and [[ethanol]].<ref name = "Yoneda_2001">{{cite journal| vauthors = Yoneda N, Kusano S, Yasui M, Pujado P, Wilcher S |title=Recent advances in processes and catalysts for the production of acetic acid|journal=Applied Catalysis A: General|volume=221|issue=1–2|pages=253–265|doi=10.1016/S0926-860X(01)00800-6|year=2001|bibcode=2001AppCA.221..253Y }}</ref>

Acetic acid can be purified via [[fractional freezing]] using an ice bath. The water and other [[Impurity|impurities]] will remain liquid while the acetic acid will [[Precipitation (chemistry)|precipitate]] out. As of 2003–2005, total worldwide production of virgin acetic acid{{efn|Acetic acid that is manufactured by intent, rather than recovered from processing (such as the production of cellulose acetates, polyvinyl alcohol operations, and numerous acetic anhydride acylations).}} was estimated at 5&nbsp;Mt/a (million tonnes per year), approximately half of which was produced in the United States. European production was approximately 1&nbsp;Mt/a and declining, while Japanese production was 0.7&nbsp;Mt/a. Another 1.5&nbsp;Mt were recycled each year, bringing the total world market to 6.5&nbsp;Mt/a.<ref name="suresh">{{cite book| vauthors = Malveda M, Funada C |year=2003|chapter-url=http://sriconsulting.com/CEH/Public/Reports/602.5000/|archive-url=https://web.archive.org/web/20111014162419/http://sriconsulting.com/CEH/Public/Reports/602.5000/|url-status=dead|archive-date=14 October 2011|chapter=Acetic Acid|title=Chemicals Economic Handbook|pages=602.5000|publisher=SRI International}}</ref><ref>{{cite journal |title=Production report|journal = Chemical & Engineering News |date=11 July 2005 |pages=67–76}}</ref> Since then, the global production has increased from 10.7 Mt/a in 2010<ref>[https://ihsmarkit.com/products/world-petro-chemical-analysis-index.html Acetic Acid] {{Webarchive|url=https://web.archive.org/web/20220423193120/https://ihsmarkit.com/products/world-petro-chemical-analysis-index.html |date=23 April 2022 }}. SRI Consulting.</ref> to 17.88 Mt/a in 2023.<ref>{{cite book |url=https://www.researchandmarkets.com/reports/4520125/acetic-acid-market-size-and-share-analysis |title=Acetic Acid Market Size & Share Analysis - Growth Trends & Forecasts (2023 - 2028) |publisher=Mordor Intelligence |year=2023 |language=en}}</ref> The two biggest producers of virgin acetic acid are [[Celanese]] and [[BP]] Chemicals. Other major producers include [[Millennium Chemicals]], [[Sterling Chemicals]], [[Samsung]], [[Eastman Chemical Company|Eastman]], and {{ill|Svensk Etanolkemi|sv}}.<ref>{{cite web|url=https://www.reportlinker.com/p02284890/Acetic-Acid.html?|title=Reportlinker Adds Global Acetic Acid Market Analysis and Forecasts|date=June 2014|work=Market Research Database|page=contents}}</ref>

=== Methanol carbonylation ===
Most acetic acid is produced by methanol [[carbonylation]]. In this process, [[methanol]] and [[carbon monoxide]] react to produce acetic acid according to the equation:

:[[File:Methanol formylation.png|class=skin-invert-image|250px]]

The process involves [[iodomethane]] as an intermediate, and occurs in three steps. A [[metal carbonyl]] [[Catalysis|catalyst]] is needed for the carbonylation (step 2).<ref name = "Yoneda_2001" />
#{{chem2|CH3OH + HI → CH3I + H2O}}
#{{chem2|CH3I + CO → CH3COI}}
#{{chem2|CH3COI + H2O → CH3COOH + HI}}

Two related processes exist for the carbonylation of methanol: the rhodium-catalyzed [[Monsanto process]], and the iridium-catalyzed [[Cativa process]]. The latter process is [[Green chemistry|greener]] and more efficient and has largely supplanted the former process.<ref name="lancaster" /> Catalytic amounts of water are used in both processes, but the Cativa process requires less, so the [[water-gas shift reaction]] is suppressed, and fewer by-products are formed.

By altering the process conditions, [[acetic anhydride]] may also be produced in plants using rhodium catalysis.<ref>{{cite journal | vauthors = Zoeller JR, Agreda VH, Cook SL, Lafferty NL, Polichnowski SW, Pond DM | title = Eastman Chemical Company Acetic Anhydride Process | journal = [[Catalysis Today]] | year = 1992 | volume = 13 | issue = 1 | pages = 73–91 | doi = 10.1016/0920-5861(92)80188-S}}</ref>

=== Acetaldehyde oxidation ===
Prior to the commercialization of the Monsanto process, most acetic acid was produced by oxidation of [[acetaldehyde]]. This remains the second-most-important manufacturing method, although it is usually not competitive with the carbonylation of methanol. The acetaldehyde can be produced by [[alkyne hydration|hydration of acetylene]]. This was the dominant technology in the early 1900s.<ref>{{cite journal|doi=10.1055/s-2007-966002|title=Catalytic Hydration of Alkynes and Its Application in Synthesis |journal=Synthesis |volume=2007 |issue=8 |pages=1121–1150 |year=2007 | vauthors = Hintermann L, Labonne A }}</ref>

Light [[naphtha]] components are readily oxidized by oxygen or even air to give [[organic peroxide|peroxides]], which decompose to produce acetic acid according to the [[chemical equation]], illustrated with [[butane]]:
:{{chem2|2 C4H10 + 5 O2 → 4 CH3CO2H + 2 H2O}}
Such oxidations require metal catalyst, such as the [[naphthenic acid|naphthenate]] [[salt (chemistry)|salt]]s of [[manganese]], [[cobalt]], and [[chromium]].

The typical reaction is conducted at [[temperature]]s and pressures designed to be as hot as possible while still keeping the butane a liquid. Typical reaction conditions are {{convert|150|C|F}} and 55&nbsp;atm.<ref>{{cite book| vauthors = Chenier PJ |title=Survey of Industrial Chemistry|edition=3rd|year=2002|publisher=Springer|isbn=978-0-306-47246-6|page=151}}</ref> Side-products may also form, including [[butanone]], [[ethyl acetate]], [[formic acid]], and [[propionic acid]]. These side-products are also commercially valuable, and the reaction conditions may be altered to produce more of them where needed. However, the separation of acetic acid from these by-products adds to the cost of the process.<ref name="Sano_1999">{{cite journal| vauthors = Sano K, Uchida H, Wakabayashi S |year=1999|title=A new process for acetic acid production by direct oxidation of ethylene|journal=Catalysis Surveys from Japan|volume=3|issue=1|pages=55–60|issn=1384-6574|doi=10.1023/A:1019003230537|s2cid=93855717}}</ref>

Similar conditions and [[catalyst]]s are used for butane oxidation, the [[oxygen]] in [[Earth's atmosphere|air]] to produce acetic acid can oxidize [[acetaldehyde]].<ref name="Sano_1999" />

:{{chem2|2 CH3CHO + O2 → 2 CH3CO2H}}

Using modern catalysts, this reaction can have an acetic acid yield greater than 95%. The major side-products are [[ethyl acetate]], [[formic acid]], and [[formaldehyde]], all of which have lower [[boiling point]]s than acetic acid and are readily separated by [[distillation]].<ref name="Sano_1999" />

=== Ethylene oxidation ===
Acetaldehyde may be prepared from [[ethylene]] via the [[Wacker process]], and then oxidized as above.

In more recent times, chemical company [[Showa Denko]], which opened an ethylene oxidation plant in [[Ōita Prefecture|Ōita]], Japan, in 1997, commercialized a cheaper single-stage conversion of ethylene to acetic acid.<ref name="Sano_1999" /> The process is catalyzed by a [[palladium]] metal catalyst supported on a [[heteropoly acid]] such as [[silicotungstic acid]]. A similar process uses the same metal catalyst on silicotungstic acid and silica:<ref name=Misono>{{cite journal | vauthors = Misono M | year = 2009 | title = Recent progress in the practical applications of heteropolyacid and perovskite catalysts: Catalytic technology for the sustainable society | journal = Catalysis Today | volume = 144 | issue = 3–4| pages = 285–291 | doi = 10.1016/j.cattod.2008.10.054}}</ref>

:{{chem2|C2H4 + O2 → CH3CO2H}}

It is thought to be competitive with methanol carbonylation for smaller plants (100–250&nbsp;kt/a), depending on the local price of ethylene.

=== Oxidative fermentation ===
For most of human history, acetic acid bacteria of the genus ''[[Acetobacter]]'' have made acetic acid, in the form of vinegar. Given sufficient oxygen, these bacteria can produce vinegar from a variety of alcoholic foodstuffs. Commonly used feeds include [[Cider|apple cider]], [[wine]], and fermented [[cereal|grain]], [[malt]], [[rice]], or [[potato]] mashes. The overall chemical reaction facilitated by these bacteria is:

:{{chem2|C2H5OH + O2 → CH3COOH + H2O}}

A dilute alcohol solution inoculated with ''Acetobacter'' and kept in a warm, airy place will become vinegar over the course of a few months. Industrial vinegar-making methods accelerate this process by improving the supply of [[oxygen]] to the bacteria.<ref>{{cite book | vauthors = Chotani GK, Gaertner AL, Arbige MV, Dodge TC |title=Kent and Riegel's Handbook of Industrial Chemistry and Biotechnology|year=2007|publisher=Springer|isbn=978-0-387-27842-1|pages=32–34|chapter=Industrial Biotechnology: Discovery to Delivery|bibcode=2007karh.book...... }}</ref>

{{failed verification span|text=The first batches of vinegar produced by fermentation probably followed errors in the [[winemaking]] process. If [[must]] is fermented at too high a temperature, acetobacter will overwhelm the [[yeast (wine)|yeast]] naturally occurring on the [[grapes]]. As the demand for vinegar for culinary, medical, and sanitary purposes increased, [[vintners]] quickly learned to use other organic materials to produce vinegar in the hot summer months before the grapes were ripe and ready for processing into wine. This method was slow, however, and not always successful, as the vintners did not understand the process.|date=April 2025}}<ref name="Hromatka" />

One of the first modern commercial processes was the "fast method" or "German method", first practised in Germany in 1823.<!-- http://www.google.de/patents?id=-stnAAAAEBAJ --> In this process, fermentation takes place in a tower packed with wood shavings or [[charcoal]]. The alcohol-containing feed is trickled into the top of the tower, and fresh [[Earth's atmosphere|air]] supplied from the bottom by either natural or forced [[convection]]. The improved air supply in this process cut the time to prepare vinegar from months to weeks.<ref>{{cite journal|title = Acetic Acid and Cellulose Acetate in the United States A General Survey of Economic and Technical Developments| vauthors = Partridge EP |journal = Industrial & Engineering Chemistry|year = 1931|volume = 23|issue =5|pages = 482–498|doi = 10.1021/ie50257a005}}</ref>

Nowadays, most vinegar is made in submerged tank [[Microbiological culture|culture]], first described in 1949 by Otto Hromatka and Heinrich Ebner.<ref>{{cite journal|title = Investigations on vinegar fermentation: Generator for vinegar fermentation and aeration procedures| vauthors = Hromatka O, Ebner H |journal = Enzymologia|volume=13|page=369|year = 1949}}</ref> In this method, alcohol is fermented to vinegar in a continuously stirred tank, and oxygen is supplied by bubbling air through the solution. Using modern applications of this method, vinegar of 15% acetic acid can be prepared in only 24 hours in batch process, even 20% in 60-hour fed-batch process.<ref name="Hromatka">{{cite journal|title = Vinegar by Submerged Oxidative Fermentation| vauthors = Hromatka O, Ebner H |journal = Industrial & Engineering Chemistry|year = 1959|volume = 51|issue = 10|pages = 1279–1280| doi = 10.1021/ie50598a033}}</ref>

=== Anaerobic fermentation ===
Species of [[anaerobic bacteria]], including members of the genus ''[[Clostridium]]'' or ''[[Acetobacterium]]'', can convert sugars to acetic acid directly without creating [[ethanol]] as an intermediate. The overall chemical reaction conducted by these bacteria may be represented as:
:{{chem2|C6H12O6 → 3 CH3COOH}}

These [[acetogen]]ic bacteria produce acetic acid from one-carbon compounds, including methanol, [[carbon monoxide]], or a mixture of [[carbon dioxide]] and [[hydrogen]]:
:{{chem2|2 CO2 + 4 H2 → CH3COOH + 2 H2O}}

This ability of ''Clostridium'' to metabolize sugars directly, or to produce acetic acid from less costly inputs, suggests that these bacteria could produce acetic acid more efficiently than ethanol-oxidizers like ''Acetobacter''. However, ''Clostridium'' bacteria are less acid-tolerant than ''Acetobacter''. Even the most acid-tolerant ''Clostridium'' strains can produce vinegar in concentrations of only a few percent, compared to ''Acetobacter'' strains that can produce vinegar in concentrations up to 20%. At present, it remains more cost-effective to produce vinegar using ''Acetobacter'', rather than using ''Clostridium'' and concentrating it. As a result, although acetogenic bacteria have been known since 1940, their industrial use is confined to a few niche applications.<ref>{{cite journal | journal = Enzyme and Microbial Technology | volume = 40 | issue = 5 | year = 2007 | pages = 1234–1243 | doi = 10.1016/j.enzmictec.2006.09.017 | title = Clostridium aceticum—A potential organism in catalyzing carbon monoxide to acetic acid: Application of response surface methodology | vauthors = Sim JH, Kamaruddin AH, Long WS, Najafpour G }}</ref>

== Uses ==
Acetic acid is a chemical [[reagent]] for the production of chemical compounds. The largest single use of acetic acid is in the production of vinyl acetate [[monomer]], closely followed by acetic anhydride and ester production. The volume of acetic acid used in vinegar is comparatively small.<ref name = Ullmann /><ref name="suresh" />

=== Vinyl acetate monomer ===
The primary use of acetic acid is the production of [[vinyl acetate]] monomer (VAM). In 2008, this application was estimated to consume a third of the world's production of acetic acid.<ref name = Ullmann /> The reaction consists of [[ethylene]] and acetic acid with [[oxygen]] over a [[palladium]] [[catalyst]], conducted in the gas phase.<ref name=vinyl-esters>{{Ullmann|title=Vinyl Esters| vauthors = Roscher G |doi=10.1002/14356007.a27_419}}</ref>
:{{chem2|2 H3C\sCOOH + 2 C2H4 + O2 → 2 H3C\sCO\sO\sCH\dCH2 + 2 H2O}}
Vinyl acetate can be polymerized to [[polyvinyl acetate]] or other [[polymers]], which are components in [[paint]]s and [[adhesive]]s.<ref name=vinyl-esters />

=== Ester production ===
The major [[ester]]s of acetic acid are commonly used as solvents for [[ink]]s, [[paint]]s and [[coating]]s. The esters include [[ethyl acetate]], ''n''-[[butyl acetate]], [[isobutyl acetate]], and [[propyl acetate]]. They are typically produced by [[catalyst|catalyzed]] reaction from acetic acid and the corresponding [[Alcohol (chemistry)|alcohol]]:
:{{chem2|CH3COO\sH + HO\sR → CH3COO\sR + H2O}}, R = general [[alkyl group]]
For example, acetic acid and [[ethanol]] gives [[ethyl acetate]] and [[water]].
:{{chem2|CH3COO\sH + HO\sCH2CH3 → CH3COO\sCH2CH3 + H2O}}

Most acetate [[esters]], however, are produced from [[acetaldehyde]] using the [[Tishchenko reaction]]. In addition, ether acetates are used as solvents for [[nitrocellulose]], [[acrylic lacquer]]s, [[varnish]] removers, and wood stains. First, glycol monoethers are produced from [[ethylene oxide]] or [[propylene oxide]] with alcohol, which are then esterified with acetic acid. The three major products are ethylene glycol monoethyl ether acetate (EEA), ethylene glycol monobutyl ether acetate (EBA), and propylene glycol monomethyl ether acetate (PMA, more commonly known as PGMEA in semiconductor manufacturing processes, where it is used as a resist solvent). This application consumes about 15% to 20% of worldwide acetic acid. Ether acetates, for example EEA, have been shown to be harmful to human reproduction.<ref name="suresh" />

=== Acetic anhydride ===
The product of the [[condensation reaction|condensation]] of two molecules of acetic acid is [[acetic anhydride]]. The worldwide production of acetic anhydride is a major application, and uses approximately 25% to 30% of the global production of acetic acid. The main process involves dehydration of acetic acid to give [[Ethenone|ketene]] at 700–750&nbsp;°C. Ketene is thereafter reacted with acetic acid to obtain the anhydride:<ref name = acetic-anh>{{Ullmann | title = Acetic Anhydride and Mixed Fatty Acid Anhydrides | vauthors = Held H, Rengstl A, Mayer D | doi = 10.1002/14356007.a01_065}}</ref>

:{{chem2|CH3CO2H → CH2\dC\dO + H2O}}
:{{chem2|CH3CO2H + CH2\dC\dO → (CH3CO)2O}}

Acetic anhydride is an [[acetylation]] agent. As such, its major application is for [[cellulose acetate]], a synthetic [[textile]] also used for [[photographic film]], which is produced by reacting cellulose with acetic acid and acetic anhydride in the presence of sulfuric acid.<ref name="Myers" /> Acetic anhydride is also a reagent for the production of [[heroin]] and other compounds.<ref name = acetic-anh />

=== Use as solvent ===
As a polar [[protic solvent]], acetic acid is frequently used for [[recrystallization (chemistry)|recrystallization]] to purify organic compounds. Acetic acid is used as a [[solvent]] in the production of [[terephthalic acid]] (TPA), the raw material for [[polyethylene terephthalate]] (PET). In 2006, about 20% of acetic acid was used for TPA production.<ref name="suresh" />

Acetic acid is often used as a solvent for reactions involving [[carbocation]]s, such as [[Friedel-Crafts#Friedel–Crafts alkylation|Friedel-Crafts alkylation]]. For example, one stage in the commercial manufacture of synthetic [[camphor]] involves a [[Wagner-Meerwein rearrangement]] of [[camphene]] to [[isobornyl acetate]]; here acetic acid acts both as a solvent and as a [[nucleophile]] to trap the [[rearrangement reaction|rearranged]] carbocation.<ref name="sell">{{cite book| vauthors = Sell CS |title=The Chemistry of Fragrances: From Perfumer to Consumer|chapter-url=https://books.google.com/books?id=G90hcKHwrqEC&pg=PA80|edition=2nd |series=RSC Paperbacks Series|volume=38|year=2006|publisher=Royal Society of Chemistry|location=Great Britain|isbn=978-0-85404-824-3|page=80|chapter=4.2.15 Bicyclic Monoterpenoids}}</ref>

Glacial acetic acid is used in analytical chemistry for the estimation of weakly alkaline substances such as organic amides. Glacial acetic acid is a much weaker [[base (chemistry)|base]] than water, so the amide behaves as a strong base in this medium. It then can be titrated using a solution in glacial acetic acid of a very strong acid, such as [[perchloric acid]].<ref name="Felgner">{{cite web |url=http://www.sigmaaldrich.com/technical-documents/articles/analytical-applications/karl-fischer/water-determination-in-perchloric-acid-0-1-mol-l-in-acetic-acid.html |title=Determination of Water Content in Perchloric acid 0,1 mol/L in acetic acid Using Karl Fischer Titration | vauthors = Felgner A |publisher=Sigma-Aldrich |access-date=27 July 2017}}</ref>

=== Medical use ===
{{Main|Acetic acid (medical use)}}
Acetic acid injection into a tumor has been used to treat cancer since the 1800s.<ref>{{cite journal| vauthors = Barclay J |title=Injection of Acetic Acid in Cancer |journal=Br Med J|year=1866|pmc=2310334|page=512|volume=2|issue=305|doi=10.1136/bmj.2.305.512-a}}</ref><ref>{{cite journal | vauthors = Yamamoto S, Iguchi Y, Shibata N, Takesue M, Tsunoda T, Sato K | title = [Percutaneous ethanol and acetic acid injection for liver metastasis from colon cancer--two case reports] | journal = Gan to Kagaku Ryoho. Cancer & Chemotherapy | volume = 25 | issue = 5 | pages = 751–755 | date = April 1998 | pmid = 9571976 }}</ref>

Acetic acid is used as part of [[cervical cancer screening]] in many areas in the [[developing world]].<ref name=Fok2015 /> The acid is applied to the [[cervix]] and if an area of white appears after about a minute the test is positive.<ref name=Fok2015>{{cite journal | vauthors = Fokom-Domgue J, Combescure C, Fokom-Defo V, Tebeu PM, Vassilakos P, Kengne AP, Petignat P | title = Performance of alternative strategies for primary cervical cancer screening in sub-Saharan Africa: systematic review and meta-analysis of diagnostic test accuracy studies | journal = BMJ | volume = 351 | pages = h3084 | date = July 2015 | pmid = 26142020 | pmc = 4490835 | doi = 10.1136/bmj.h3084 }}</ref>

Acetic acid is an effective antiseptic when used as a 1% solution, with broad spectrum of activity against streptococci, staphylococci, pseudomonas, enterococci and others.<ref>{{cite journal | vauthors = Madhusudhan VL | title = Efficacy of 1% acetic acid in the treatment of chronic wounds infected with Pseudomonas aeruginosa: prospective randomized controlled clinical trial | journal = International Wound Journal | volume = 13 | issue = 6 | pages = 1129–1136 | date = December 2016 | pmid = 25851059 | pmc = 7949569 | doi = 10.1111/iwj.12428 | s2cid = 4767974 }}</ref><ref>{{cite journal | vauthors = Ryssel H, Kloeters O, Germann G, Schäfer T, Wiedemann G, Oehlbauer M | title = The antimicrobial effect of acetic acid--an alternative to common local antiseptics? | journal = Burns | volume = 35 | issue = 5 | pages = 695–700 | date = August 2009 | pmid = 19286325 | doi = 10.1016/j.burns.2008.11.009 }}</ref><ref>{{cite web|url=https://www.medscape.com/viewarticle/456300_4|title=Antiseptics on Wounds: An Area of Controversy|website=www.medscape.com|access-date=15 August 2016}}</ref> It may be used to treat skin infections caused by pseudomonas strains resistant to typical antibiotics.<ref>{{cite journal | vauthors = Nagoba BS, Selkar SP, Wadher BJ, Gandhi RC | title = Acetic acid treatment of pseudomonal wound infections--a review | journal = Journal of Infection and Public Health | volume = 6 | issue = 6 | pages = 410–415 | date = December 2013 | pmid = 23999348 | doi = 10.1016/j.jiph.2013.05.005 | doi-access = free }}</ref>

While diluted acetic acid is used in [[iontophoresis]], no high quality evidence supports this treatment for rotator cuff disease.<ref>{{cite journal | vauthors = Page MJ, Green S, Mrocki MA, Surace SJ, Deitch J, McBain B, Lyttle N, Buchbinder R | title = Electrotherapy modalities for rotator cuff disease | journal = The Cochrane Database of Systematic Reviews | volume = 2016 | issue = 6 | pages = CD012225 | date = June 2016 | pmid = 27283591 | pmc = 8570637 | doi = 10.1002/14651858.CD012225 }}</ref><ref>{{cite book| vauthors = Habif TP |title=Clinical Dermatology|date=2009|publisher=Elsevier Health Sciences|isbn=978-0-323-08037-8|page=367|edition=5th|url=https://books.google.com/books?id=kDWlWR5UbqQC&pg=PA367}}</ref>

As a treatment for [[otitis externa]], it is on the [[WHO Model List of Essential Medicines|World Health Organization's List of Essential Medicines]].<ref name="WHO23rd">{{cite book | vauthors = ((World Health Organization)) | title = The selection and use of essential medicines 2023: web annex A: World Health Organization model list of essential medicines: 23rd list (2023) | year = 2023 | hdl = 10665/371090 | author-link = World Health Organization | publisher = World Health Organization | location = Geneva | id = WHO/MHP/HPS/EML/2023.02 | hdl-access=free }}</ref>

=== Foods ===
{{Main|Vinegar}}
Acetic acid has {{cvt|349|kcal|kJ}} per 100&nbsp;g.<ref name="FAOSouthgate">{{cite book| vauthors = Greenfield H, Southgate D |date=2003|title=Food Composition Data: Production, Management and Use|location=Rome|publisher=[[FAO]]|page=146|isbn=9789251049495}}</ref> Vinegar is typically no less than 4% acetic acid by mass.<ref>{{cite web|url=https://www.fda.gov/ucm/groups/fdagov-public/@fdagov-afda-ice/documents/webcontent/ucm074471.pdf|archive-url=https://web.archive.org/web/20180124165105/https://www.fda.gov/ucm/groups/fdagov-public/@fdagov-afda-ice/documents/webcontent/ucm074471.pdf|url-status=dead|archive-date=24 January 2018|title=CPG Sec. 525.825 Vinegar, Definitions|publisher=United States Food and Drug Administration|date=March 1995}}</ref><ref>{{cite web|url=https://laws-lois.justice.gc.ca/PDF/C.R.C.,_c._870.pdf|title=Departmental Consolidation of the Food and Drugs Act and the Food and Drug Regulations – Part B – Division 19|publisher=Health Canada|date=August 2018|page=591}}</ref><ref>{{cite web|url=https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32016R0263&from=EN|title=Commission Regulation (EU) 2016/263|work=Official Journal of the European Union|publisher=European Commission|date=February 2016}}</ref> Legal limits on acetic acid content vary by jurisdiction. Vinegar is used directly as a [[condiment]], and in the [[pickling]] of vegetables and other foods. Table vinegar tends to be more diluted (4% to 8% acetic acid), while commercial food pickling employs solutions that are more concentrated. The proportion of acetic acid used worldwide as vinegar is not as large as industrial uses, but it is by far the oldest and best-known application.<ref>{{cite book| vauthors = Bernthsen A, Sudborough JJ |title=Organic Chemistry|url=https://archive.org/details/in.ernet.dli.2015.513637|year=1922|publisher=Blackie and Son|location=London|page=155}}</ref>

== Reactions ==
=== Organic chemistry ===

{{Image frame|align=none|caption=Two typical organic reactions of acetic acid|width=400|innerstyle=display:flex;|content=<!--
-->{{Biochem reaction subunit|compound=acetyl chloride|image=Acetyl chloride.svg|class=skin-invert-image|imagesize=80px}}<!--
-->{{Biochem reaction subunit|direction=reverse|imagesize=60px|overarrow=[[Thionyl chloride|{{chem2|SOCl2}}]]}}<!--
-->{{Biochem reaction subunit|compound=acetic acid|image=Acetic acid Structural Formula V1.svg|class=skin-invert-image|imagesize=80px}}<!--
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Acetic acid undergoes the typical [[chemical reaction]]s of a carboxylic acid. Upon treatment with a standard base, it converts to metal [[acetate]] and [[water]]. With strong bases (e.g., organolithium reagents), it can be doubly deprotonated to give {{chem2|LiCH2COOLi}}. Reduction of acetic acid gives ethanol. The OH group is the main site of reaction, as illustrated by the conversion of acetic acid to [[acetyl chloride]]. Other substitution derivatives include [[acetic anhydride]]; this [[anhydride]] is produced by [[Condensation reaction|loss of water]] from two molecules of acetic acid. [[Ester]]s of acetic acid can likewise be formed via [[Fischer esterification]], and [[amide]]s can be formed. When heated above {{convert|440|C|F}}, acetic acid decomposes to produce [[carbon dioxide]] and [[methane]], or to produce [[ketene]] and water:<ref>{{cite journal|title=The thermal decomposition of acetic acid|journal=Journal of the Chemical Society B: Physical Organic|year=1968|pages=1153–1155| vauthors = Blake PG, Jackson GE |doi=10.1039/J29680001153}}</ref><ref>{{cite journal|journal=Journal of the Chemical Society|year=1949|title=608. The thermal decomposition of acetic acid| vauthors = Bamford CH, Dewar MJ|doi=10.1039/JR9490002877|pages=2877}}</ref><ref name="Duan1995">{{cite journal| vauthors = Duan X, Page M |year=1995|title=Theoretical Investigation of Competing Mechanisms in the Thermal Unimolecular Decomposition of Acetic Acid and the Hydration Reaction of Ketene|journal=Journal of the American Chemical Society|volume=117|issue=18|pages=5114–5119|issn=0002-7863|doi=10.1021/ja00123a013|bibcode=1995JAChS.117.5114D }}</ref>

:{{chem2|CH3COOH → CH4 + CO2}}
:{{chem2|CH3COOH → CH2\dC\dO + H2O}}

=== Reactions with inorganic compounds ===
Acetic acid is mildly [[corrosion|corrosive]] to [[metal]]s including [[iron]], [[magnesium]], and [[zinc]], forming [[hydrogen]] gas and salts called [[acetate]]s:
:{{chem2|Mg + 2 CH3COOH → (CH3COO)2Mg + H2}}
Because [[aluminium]] forms a [[Passivation (chemistry)|passivating]] acid-resistant film of [[aluminium oxide]], aluminium tanks are used to transport acetic acid.<ref>{{Cite journal |date=1957-11-01 |title=Corrosion by Acetic Acid—A Report of Task Group T-5A-3 On Corrosion by Acetic Acid (1) |url=https://meridian.allenpress.com/corrosion/article/13/11/79/156728/Corrosion-by-Acetic-Acid-A-Report-of-Task-Group-T |journal=Corrosion |language=en |volume=13 |issue=11 |pages=79–88 |doi=10.5006/0010-9312-13.11.79 |issn=1938-159X|url-access=subscription }}</ref> Containers lined with glass, [[stainless steel]] or [[polyethylene]] are also used for this purpose.<ref name="Ullmann" /> Metal acetates can also be prepared from acetic acid and an appropriate [[Base (chemistry)|base]], as in the popular "[[Sodium bicarbonate|baking soda]] + vinegar" reaction giving off [[sodium acetate]]:
:{{chem2|NaHCO3 + CH3COOH → CH3COONa + CO2 + H2O}}

A [[colour reaction]] for salts of acetic acid is [[iron(III) chloride]] solution, which results in a deeply red colour that disappears after acidification.<ref name="Charlot">{{cite book| vauthors = Charlot G, Murray RG |title=Qualitative Inorganic Analysis|url=https://books.google.com/books?id=rzI9AAAAIAAJ&pg=PA110|edition=4th|year=1954|publisher=CUP Archive|page=110}}</ref> A more sensitive test uses [[lanthanum nitrate]] with iodine and ammonia to give a blue solution.<ref name="Neelakantam">{{cite web|url=http://repository.ias.ac.in/33062/1/33062.pdf|title=The Lanthanum Nitrate Test for Acetatein Inorganic Qualitative Analysis| vauthors = Neelakantam K, Row LR |year=1940|access-date=June 5, 2013}}</ref> Acetates when heated with [[arsenic trioxide]] form [[cacodyl oxide]], which can be detected by its [[odour|malodorous]] vapours.<ref name="Brantley1947">{{cite journal| vauthors = Brantley LR, Cromwell TM, Mead JF |year=1947 |title=Detection of acetate ion by the reaction with arsenious oxide to form cacodyl oxide|journal=Journal of Chemical Education |volume=24 |issue=7 |page=353 |issn=0021-9584 |doi=10.1021/ed024p353 |bibcode=1947JChEd..24..353B}}</ref>

=== Other derivatives ===
Organic or inorganic salts are produced from acetic acid. Some commercially significant derivatives:
*[[Sodium acetate]], used in the [[textile]] industry and as a food [[preservative]] ([[E number|E262]]).
*[[Copper(II) acetate]], used as a [[pigment]] and a [[fungicide]].
*[[Aluminium acetate]] and [[iron(II) acetate]]—used as [[mordant]]s for [[dye]]s.
*[[Palladium(II) acetate]], used as a catalyst for organic coupling reactions such as the [[Heck reaction]].

Halogenated acetic acids are produced from acetic acid. Some commercially significant derivatives:
*[[Chloroacetic acid]] (monochloroacetic acid, MCA), dichloroacetic acid (considered a by-product), and [[trichloroacetic acid]]. MCA is used in the manufacture of [[indigo dye]].
*[[Bromoacetic acid]], which is esterified to produce the reagent [[ethyl bromoacetate]].
*[[Trifluoroacetic acid]], which is a common reagent in [[organic synthesis]].

Amounts of acetic acid used in these other applications together account for another 5–10% of acetic acid use worldwide.<ref name="suresh" />

== Health and safety ==

=== Vapour ===
Prolonged inhalation exposure (eight hours) to acetic acid vapours at 10 ppm can produce some irritation of eyes, nose, and throat; at 100 ppm marked lung irritation and possible damage to lungs, eyes, and skin may result. Vapour concentrations of 1,000 ppm cause marked irritation of eyes, nose and upper respiratory tract and cannot be tolerated. These predictions were based on [[Animal testing|animal experiments]] and industrial exposure.<ref name="CDC">{{cite web |title=Occupational Safety and Health Guideline for Acetic Acid |url=https://www.cdc.gov/niosh/docs/81-123/pdfs/0002-rev.pdf |url-status=dead |archive-url=https://web.archive.org/web/20200308110415/https://www.cdc.gov/niosh/docs/81-123/pdfs/0002-rev.pdf |archive-date=8 March 2020 |access-date=May 8, 2013 |publisher=Centers for Disease Control and Prevention}}</ref>

In 12 workers exposed for two or more years to an airborne average concentration of 51 ppm acetic acid (estimated), symptoms of conjunctive irritation, upper respiratory tract irritation, and hyperkeratotic dermatitis were produced. Exposure to 50 ppm or more is intolerable to most persons and results in intensive [[Tears|lacrimation]] and irritation of the eyes, nose, and throat, with pharyngeal oedema and chronic bronchitis. Unacclimatized humans experience extreme eye and nasal irritation at concentrations in excess of 25 ppm, and conjunctivitis from concentrations below 10 ppm has been reported. In a study of five workers exposed for seven to 12 years to concentrations of 80 to 200 ppm at peaks, the principal findings were blackening and hyperkeratosis of the skin of the hands, conjunctivitis (but no corneal damage), bronchitis and pharyngitis, and erosion of the exposed teeth (incisors and canines).<ref name=":0">{{cite book|publisher=Virginia Department of Health Division of Health Hazards Control| vauthors = Sherertz PC |date=June 1, 1994|title=Acetic Acid|url=http://www.vdh.virginia.gov/epidemiology/DEE/PublicHealthToxicology/documents/pdf/aceticacid.PDF|archive-url=https://web.archive.org/web/20160304110629/http://www.vdh.virginia.gov/epidemiology/DEE/PublicHealthToxicology/documents/pdf/aceticacid.PDF|url-status=dead|archive-date=4 March 2016}}</ref>

=== Solution ===

Concentrated acetic acid (≥ 25%) is [[corrosion|corrosive]] to skin.<ref name="IPCS card">{{cite web|url=https://www.inchem.org/documents/icsc/icsc/eics0363.htm|title=ICSC 0363 – ACETIC ACID|publisher=International Programme on Chemical Safety|date=June 5, 2010}}</ref> These burns or blisters may not appear until hours after exposure.<ref>{{cite web |title=Standard Operating Procedure Glacial Acetic Acid |url=https://chemistry.ucmerced.edu/sites/chemistry.ucmerced.edu/files/page/documents/ejm_acetic_acid.pdf |publisher=UCMERCED |access-date=19 February 2024 |date=19 October 2012}}</ref> The hazardous properties of acetic acid are dependent on the concentration of the (typically [[Aqueous solution|aqueous]]) solution, with the most significant increases in hazard levels at thresholds of 25% and 90% acetic acid concentration by weight. The following table summarizes the hazards of acetic acid solutions by concentration:<ref name=ECHA>{{cite web |title=C&L Inventory |url=https://echa.europa.eu/information-on-chemicals/cl-inventory-database/-/discli/details/85625 |access-date=2023-12-13 |website=echa.europa.eu}}</ref>
{| class="wikitable"
|-
! [[Concentration]]<br />by weight
! Molarity
! [[GHS hazard pictograms|GHS pictograms]]
! [[List of H-phrases|H-Phrases]]
|-
| 10–25%
| 1.67–4.16&nbsp;mol/L
| {{GHS07}}
| {{H-phrases|315}}
|-
| 25–90%
| 4.16–14.99&nbsp;mol/L
| {{GHS05}}
| {{H-phrases|314}}
|-
| >90%
| >14.99&nbsp;mol/L
| {{GHS02}}{{GHS05}}
| {{H-phrases|226|314}}
|}

Concentrated acetic acid can be ignited only with difficulty at standard temperature and pressure, but becomes a flammable risk in temperatures greater than {{convert|39|C|F}}, and can form explosive mixtures with air at higher temperatures with [[explosive limit]]s of 5.4–16% concentration.

== See also ==
*[[Acetic acid (data page)]]
*[[Acids in wine]]

==Notes==
{{Notelist|colwidth=30em}}

== References ==
{{Reflist|colwidth=30em}}
<!-- Dead note "calcs": Mooij, W.T.M.; van Eijck, B.P.; Price, S.L.; Verwer, P.; Kroon, J. (1998). "Crystal structure predictions for acetic acid". ''J. Computat. Chem.'' '''19''', 459. -->

== External links ==
{{Wiktionary|acetic}}
{{Commons}}
*{{ICSC|0363|03}}
*[http://www.npi.gov.au/resource/acetic-acid-ethanoic-acid National Pollutant Inventory – Acetic acid fact sheet]
*[https://www.cdc.gov/niosh/npg/npgd0002.html NIOSH Pocket Guide to Chemical Hazards]
*[https://www.cdc.gov/niosh/docs/2003-154/pdfs/1603.pdf Method for sampling and analysis]
*[https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1000TABLEZ1 29 CFR 1910.1000, Table Z-1] (US Permissible exposure limits)
*[http://chemsub.online.fr/name/Acetic_acid.html ChemSub Online: Acetic acid]
*Calculation of [http://ddbonline.ddbst.de/AntoineCalculation/AntoineCalculationCGI.exe?component=Acetic+acid vapor pressure], [http://ddbonline.ddbst.de/DIPPR105DensityCalculation/DIPPR105CalculationCGI.exe?component=Acetic+acid liquid density], [http://ddbonline.ddbst.de/VogelCalculation/VogelCalculationCGI.exe?component=Acetic+acid dynamic liquid viscosity], [http://ddbonline.ddbst.de/DIPPR106SFTCalculation/DIPPR106SFTCalculationCGI.exe?component=Acetic+acid surface tension] of acetic acid
*[http://www.ebi.ac.uk/pdbe-srv/PDBeXplore/ligand/?ligand=ACT Acetic acid bound to proteins] in the [[Protein Data Bank|PDB]]
*[https://web.archive.org/web/20150207065434/http://apps.kemi.se/flodessok/floden/kemamne_eng/attiksyra_eng.htm Swedish Chemicals Agency. Information sheet – Acetic Acid]
* Process Flow sheet of Acetic acid Production by the [https://web.archive.org/web/20141102121127/http://www.inclusive-science-engineering.com/processes-for-manufacturing-acetic-acid/acetic-acid/ Carbonylation of Methanol]

{{Gynecological anti-infectives and antiseptics}}
{{Otologicals}}
{{Fatty acids}}
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{{Acetates}}
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{{Authority control}}

[[Category:Acetic acids| ]]
[[Category:Acids in wine]]
[[Category:Antiseptics]]
[[Category:Commodity chemicals]]
[[Category:E-number additives]]
[[Category:Flavors]]
[[Category:Household chemicals]]
[[Category:Otologicals]]
[[Category:Photographic chemicals]]
[[Category:Solvents]]
[[Category:World Health Organization essential medicines]]
[[Category:Organic compounds with 2 carbon atoms]]
[[Category:Acetyl compounds]]