View source for Butyric acid

{{Short description|Chemical compound (CH3CH2CH2COOH)}}
{{Use dmy dates|date=March 2016}}
{{Chembox
|ImageFileL1 = Butyric acid acsv.svg
|ImageClassL1= skin-invert 
|ImageSizeL1 = 100px
|ImageNameL1 = Skeletal structure of butyric acid
|ImageFileR1 = Butyric_acid_flat_structure.png
|ImageClassR1 = skin-invert 
|ImageSizeR1 = 100px
|ImageNameR1 = Flat structure of butyric acid
|ImageFile2 = Butyric-acid-3D-balls.png
|ImageClass2 = bg-transparent  
|ImageName2 = Space filling model of butyric acid
|PIN = Butanoic acid<ref name=iupac2013>{{cite book |title=Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = [[Royal Society of Chemistry|The Royal Society of Chemistry]] | date = 2014 | location = Cambridge | page = 746 | doi = 10.1039/9781849733069-00648 | isbn = 978-0-85404-182-4 | chapter = Applications to Specific Classes of Compounds}}</ref>
|OtherNames = Ethylacetic acid<br />1-Propanecarboxylic acid<br />Propylformic acid<br />C4:0 ([[Lipid number]]s)
|Section1={{Chembox Identifiers
|index_label = Butyric acid
|index1_label = Butyrate
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = 40UIR9Q29H
|ChEMBL_Ref = {{ebicite|correct|EBI}}
|ChEMBL = 14227
|KEGG_Ref = {{keggcite|correct|kegg}}
|KEGG = C00246
|InChI = 1/C4H8O2/c1-2-3-4(5)6/h2-3H2,1H3,(H,5,6)
|InChIKey = FERIUCNNQQJTOY-UHFFFAOYAP
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|StdInChI = 1S/C4H8O2/c1-2-3-4(5)6/h2-3H2,1H3,(H,5,6)
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey = FERIUCNNQQJTOY-UHFFFAOYSA-N
|CASNo_Ref = {{cascite|correct|CAS}}
|CASNo = 107-92-6
|CASNo1 = 461-55-2
|CASNo1_Ref = {{cascite|correct|CAS}}
|PubChem = 264
|PubChem1 = 104775
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 259
|ChemSpiderID1 = 94582
|ChemSpiderID1_Ref = {{chemspidercite|correct|chemspider}}
|UNNumber = 2820
|EINECS = 203-532-3
|RTECS = ES5425000
|IUPHAR_ligand = 1059
|ChEBI_Ref = {{ebicite|correct|EBI}}
|ChEBI = 30772
|DrugBank_Ref = {{drugbankcite|correct|drugbank}}
|DrugBank = DB03568
|SMILES = O=C(O)CCC
|MeSHName = Butyric+acid
}}
|Section2={{Chembox Properties
|C=4 | H=8 | O=2
|Formula = {{Chem|C|3|H|7|COOH}}
|Appearance = Colorless liquid
|Odor = Unpleasant, similar to vomit or body odor
|Density = 1.135 g/cm<sup>3</sup> (−43 °C)<ref name=csba /><br/> 0.9528 g/cm<sup>3</sup> (25 °C)<ref name=crc />
|MeltingPtC = −5.1
|MeltingPt_ref = <ref name=crc>{{CRC90}}</ref>
|BoilingPtC = 163.75
|BoilingPt_ref = <ref name=crc />
|SublimationConditions = Sublimes at −35&nbsp;°C<br/> Δ<sub>subl</sub>''H''<sup><s>o</s></sup> = 76 kJ/mol<ref name=nist />
|Solubility = Miscible
|SolubleOther = Miscible with [[ethanol]], [[diethyl ether|ether]]. Slightly soluble in [[carbon tetrachloride|CCl<sub>4</sub>]]
|pKa = 4.82
|RefractIndex = 1.398 (20 °C)<ref name=crc />
|Viscosity = 1.814 c[[Poise (unit)|P]] (15 °C)<ref name=chemister>{{cite web|url=http://chemister.ru/Database/properties-en.php?dbid=1&id=1985 |title=Butanoic acid |publisher=Chemister.ru |date=2007-03-19 |access-date=2020-10-27}}</ref><br/> 1.426 cP (25 °C)
|VaporPressure = 0.112 kPa (20 °C)<br/> 0.74 kPa (50 °C)<br/> 9.62 kPa (100 °C)<ref name=nist />
|LogP = 0.79
|HenryConstant = 5.35·10<sup>−4</sup> L·atm/mol
|ThermalConductivity = 1.46·10<sup>5</sup> W/m·K
|MagSus = −55.10·10<sup>−6</sup> cm<sup>3</sup>/mol
}}
|Section3={{Chembox Structure
|Dipole = 0.93 D (20 °C)<ref name=chemister />
|CrystalStruct = [[monoclinic crystal system|Monoclinic]] (−43 °C)<ref name=csba>{{Cite journal | doi = 10.1107/S0365110X6200328X| title = Crystal structure of butyric acid| journal = Acta Crystallographica| volume = 15| issue = 12| pages = 1240–1244| year = 1962| last1 = Strieter | first1 = F. J.| last2 = Templeton | first2 = D. H.| bibcode = 1962AcCry..15.1240S| name-list-style = vanc| url = https://escholarship.org/content/qt2576b18r/qt2576b18r.pdf?t=p0llqf}}</ref>
|SpaceGroup = C2/m<ref name=csba />
|LattConst_a = 8.01 Å
|LattConst_b = 6.82 Å
|LattConst_c = 10.14 Å<ref name=csba />
|LattConst_alpha =
|LattConst_beta = 111.45
}}
|Section4={{Chembox Thermochemistry
|HeatCapacity = 178.6 J/mol·K<ref name=nist />
|DeltaHf = −533.9 kJ/mol<ref name=nist>{{nist|name=Butanoic acid| id= C107926|accessdate=27 October 2020|mask=FFFF|units=SI}}</ref>
|Entropy = 222.2 J/mol·K<ref name=chemister />
|DeltaHc = 2183.5 kJ/mol<ref name=nist />
}}
|Section5={{Chembox Hazards
|ExternalSDS = [https://www.bio.vu.nl/~microb/Protocols/chemicals/MSDS/butyric%20acid.pdf External MSDS]| GHSPictograms = {{GHS05}}<ref name="sigma">{{Sigma-Aldrich| id= w222119|name=Butyric acid|accessdate=27 October 2020}}</ref>
|GHSSignalWord = Danger
|HPhrases = {{H-phrases|314}}<ref name="sigma" />
|PPhrases = {{P-phrases|280|305+351+338|310}}<ref name="sigma" />
|FlashPtC = 71 to 72
|FlashPt_ref = <ref name="sigma" />
|AutoignitionPtC = 440
|AutoignitionPt_ref = <ref name="sigma" />
|ExploLimits = 2.2–13.4%
|NFPA-H = 3
|NFPA-F = 2
|NFPA-R = 0
|LD50 = 2000 mg/kg (oral, rat)
}}
|Section6={{Chembox Related
|OtherFunction_label = [[carboxylic acid]]s
|OtherFunction = [[Propionic acid]], [[Pentanoic acid]]
|OtherCompounds = [[1-Butanol]]<br/> [[Butyraldehyde]]<br/> [[Methyl butyrate]]
}}
}}

'''Butyric acid''' ({{IPAc-en|b|j|uː|ˈ|t|ɪ|r|ɪ|k}}; from {{langx|grc|βούτῡρον}}, meaning "butter"), also known under the systematic name '''butanoic acid''', is a straight-chain [[alkyl]] [[carboxylic acid]] with the [[chemical formula]] {{chem2|CH3CH2CH2COOH}}. It is an oily, colorless liquid with an unpleasant odor. [[Isobutyric acid]] (2-methylpropanoic acid) is an [[isomer]]. [[Carboxylate salt|Salts]] and [[ester]]s of butyric acid are known as '''butyrates''' or '''butanoates'''. The acid does not occur widely in nature, but its esters are widespread. It is a common industrial chemical<ref name=Ullmann>{{Ullmann|first1=Wilhelm|last1=Riemenschneider|title=Carboxylic Acids, Aliphatic|year=2002|doi=10.1002/14356007.a05_235}}</ref> and an important component in the mammalian gut.

==History==
Butyric acid was first observed in an impure form in 1814 by the French chemist [[Michel Eugène Chevreul]]. By 1818, he had purified it sufficiently to characterize it. However, Chevreul did not publish his early research on butyric acid; instead, he deposited his findings in manuscript form with the secretary of the [[Academy of Science of France|Academy of Sciences]] in Paris, France. [[Henri Braconnot]], another French chemist, was also researching the composition of butter and was publishing his findings and this led to disputes about priority. As early as 1815, Chevreul claimed that he had found the substance responsible for the smell of butter.<ref>Chevreul (1815) [https://books.google.com/books?id=tZU5AAAAcAAJ&pg=PA73 "Lettre de M. Chevreul à MM. les rédacteurs des Annales de chimie"] (Letter from Mr. Chevreul to the editors of the Annals of Chemistry), ''Annales de chimie'', '''94''' : 73–79; in a footnote spanning pp. 75–76, he mentions that he had found a substance that is responsible for the smell of butter.</ref> By 1817, he published some of his findings regarding the properties of butyric acid and named it.<ref>Chevreul (1817) [https://books.google.com/books?id=y1E3AAAAYAAJ&pg=PA79 "Extrait d'une lettre de M. Chevreul à MM. les Rédacteurs du Journal de Pharmacie"] (Extract of a letter from Mr. Chevreul to the editors of the Journal of Pharmacy), ''Journal de Pharmacie et des sciences accessoires'', '''3''' : 79–81. On p. 81, he named butyric acid: ''"Ce principe, que j'ai appelé depuis acid butérique, … "'' (This principle [i.e., constituent], which I have since named "butyric acid", … )</ref> However, it was not until 1823 that he presented the properties of butyric acid in detail.<ref>E. Chevreul, ''Recherches chimiques sur les corps gras d'origine animale'' [Chemical researches on fatty substances of animal origin] (Paris, France: F.G. Levrault, 1823), [https://archive.org/details/rechercheschimi00chevgoog/page/n144 pages 115–133].</ref> The name butyric acid comes from {{wikt-lang|grc|βούτῡρον}}, meaning "butter", the substance in which it was first found. The Latin name ''butyrum'' (or ''buturum'') is similar.

==Occurrence==
[[Triglyceride]]s of butyric acid make up 3–4% of [[butter]]. When butter goes [[Rancidification|rancid]], butyric acid is liberated from the glyceride by [[hydrolysis]].<ref>{{cite journal |doi=10.3168/jds.S0022-0302(83)82052-9 |title=Stepwise Discriminant Analysis of Free Fatty Acid Profiles for Identifying Sources of Lipolytic Enzymes in Rancid Butter |year=1983 |last1=Woo |first1=A.H. |last2=Lindsay |first2=R.C. |journal=Journal of Dairy Science |volume=66 |issue=10 |pages=2070–2075 |doi-access=free }}</ref> It is one of the fatty acid subgroup called [[short-chain fatty acid]]s. Butyric acid is a typical [[carboxylic acid]] that reacts with bases and affects many metals.<ref name="inchem1">[http://www.inchem.org/documents/icsc/icsc/eics1334.htm ICSC 1334 – Butyric acid]. Inchem.org (23 November 1998). Retrieved on 2020-10-27.</ref>
It is found in [[animal fat]] and [[Types of plant oils|plant oil]]s, [[Bovinae|bovine]] [[milk]], [[breast milk]], [[butter]], [[parmesan cheese]], [[body odor]], and [[vomit]] as a product of anaerobic [[fermentation (biochemistry)|fermentation]] (including in the [[colon (anatomy)|colon]]).<ref name="morrison">{{cite journal|pmc=4939913|year=2016|last1=Morrison|first1=D. J.|title=Formation of short chain fatty acids by the gut microbiota and their impact on human metabolism|journal=Gut Microbes|volume=7|issue=3|pages=189–200|last2=Preston|first2=T.|pmid=26963409|doi=10.1080/19490976.2015.1134082}}</ref> It has a [[taste]] somewhat like butter and an unpleasant [[odor]]. [[Mammal]]s with good scent detection abilities, such as [[dog]]s, can detect it at 10 [[parts per billion]], whereas [[human]]s can detect it only in concentrations above 10 [[parts per million]]. In [[food industry|food manufacturing]], it is used as a [[Flavoring|flavoring agent]].<ref>{{cite web |url=http://www.thegoodscentscompany.com/data/rw1003411.html |title=Butyric acid |website=The Good Scents Company |access-date=2020-10-26}}</ref>

In humans, butyric acid is one of two primary [[endogenous agonist]]s of human [[hydroxycarboxylic acid receptor&nbsp;2]] ({{chem2|HCA2}}), a {{nowrap|[[Gi alpha subunit|G<sub>i/o</sub>-coupled]]}} [[G protein-coupled receptor]].<ref name="IUPHAR's comprehensive 2011 review on HCARs">{{cite journal | vauthors = Offermanns S, Colletti SL, Lovenberg TW, Semple G, Wise A, IJzerman AP | title = International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B) | journal = Pharmacological Reviews | volume = 63 | issue = 2 | pages = 269–290 | date = June 2011 | pmid = 21454438 | doi = 10.1124/pr.110.003301 | doi-access = free}}</ref><ref name="IUPHAR-DB HCAR family page">{{cite web |vauthors = Offermanns S, Colletti SL, IJzerman AP, Lovenberg TW, Semple G, Wise A, Waters MG |title=Hydroxycarboxylic acid receptors |url=http://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=48 |website=IUPHAR/BPS Guide to Pharmacology |publisher=International Union of Basic and Clinical Pharmacology |access-date=13 July 2018}}</ref>

Butyric acid is present as its [[Ester#List of ester odorants|octyl ester]] in [[parsnip]] (''Pastinaca sativa'')<ref>{{cite journal|doi=10.1023/A:1021093114663|pmid=12523562|year=2002|last1=Carroll|first1=Mark J.|title=Behavioral responses of the parsnip webworm to host plant volatiles|journal=Journal of Chemical Ecology|volume=28|issue=11|pages=2191–2201|last2=Berenbaum|first2=May R.|bibcode=2002JCEco..28.2191C |s2cid=23512190}}
</ref> and in the seed of the [[Ginkgo biloba|ginkgo tree]].<ref>{{cite book|last1=Raven|first1=Peter H.|author-link1=Peter H. Raven|last2=Evert|first2=Ray F.|last3=Eichhorn|first3=Susan E.|title=Biology of Plants|url=https://archive.org/details/biologyofplants00rave_0|url-access=registration|access-date=11 October 2018|year=2005|publisher=W. H. Freemanand Company|isbn=978-0-7167-1007-3|pages=[https://archive.org/details/biologyofplants00rave_0/page/429 429]–431}}</ref>

==Production==
===Industrial===
In industry, butyric acid is produced by [[hydroformylation]] from [[propene]] and [[syngas]], forming [[butyraldehyde]], which is [[oxidised]] to the final product.<ref name=Ullmann/>

{{block indent| {{chem2|H2 + CO + CH3CH\dCH2 → CH3CH2CH2CHO}}{{overset|oxidation|→}}butyric acid}}

It can be separated from aqueous solutions by saturation with salts such as [[calcium chloride]]. The calcium salt, {{chem2|Ca(C4H7O2)2 '''·''' H2O}}, is less soluble in hot water than in cold.

===Microbial biosynthesis===
[[File:ButyrateBisyn.svg|thumb|left|144px|One pathway for butyrate biosynthesis. Relevant enzymes: acetoacetyl-CoA thiolase, NAD- and NADP-dependent 3-hydroxybutyryl-CoA dehydrogenase, 3-hydroxybutyryl-CoA dehydratase, and NAD-dependent butyryl-CoA dehydrogenase.]]
Butyrate is produced by several fermentation processes performed by [[Obligate anaerobe|obligate]] [[anaerobic organism|anaerobic]] [[bacteria]].<ref>{{cite journal|doi=10.1073/pnas.0711093105|pmid=18218779|pmc=2542871|title=The Genome of ''Clostridium kluyveri'', a Strict Anaerobe with Unique Metabolic Features|journal=Proceedings of the National Academy of Sciences|volume=105|issue=6|pages=2128–2133|year=2008|last1=Seedorf|first1=H.|last2=Fricke|first2=W. F.|last3=Veith|first3=B.|last4=Bruggemann|first4=H.|last5=Liesegang|first5=H.|last6=Strittmatter|first6=A.|last7=Miethke|first7=M.|last8=Buckel|first8=W.|last9=Hinderberger|first9=J.|last10=Li|first10=F.|last11=Hagemeier|first11=C.|last12=Thauer|first12=R. K.|last13=Gottschalk|first13=G.|bibcode=2008PNAS..105.2128S|doi-access=free}}
</ref> This fermentation pathway was discovered by [[Louis Pasteur]] in 1861. Examples of butyrate-producing [[species]] of bacteria:

* ''[[Clostridium butyricum]]''
* ''[[Clostridium kluyveri]]''
* ''[[Clostridium pasteurianum]]''
* ''[[Faecalibacterium prausnitzii]]''
* ''[[Fusobacterium nucleatum]]''
* ''[[Butyrivibrio fibrisolvens]]''
* ''Eubacterium limosum''

The pathway starts with the [[glycolysis|glycolytic]] cleavage of [[glucose]] to two [[molecule]]s of [[pyruvate]], as happens in most organisms. Pyruvate is [[oxidation|oxidized]] into [[acetyl coenzyme A]] catalyzed by [[pyruvate:ferredoxin oxidoreductase]]. Two molecules of [[carbon dioxide]] ({{chem2|CO2}}) and two molecules of [[hydrogen]] ({{chem2|H2}}) are formed as waste products. Subsequently, {{abbr|ATP|adenosine triphosphate}} is produced in the last step of the fermentation. Three molecules of ATP are produced for each glucose molecule, a relatively high yield. The balanced equation for this fermentation is

{{block indent| {{chem2|C6H12O6 → C4H8O2 + 2CO2 + 2H2}}}}

Other pathways to butyrate include [[succinate]] reduction and crotonate disproportionation.

{| class="wikitable"
|-
!Action!!Responsible enzyme
|-
| Acetyl coenzyme A converts into [[acetoacetyl coenzyme A]] || [[acetyl-CoA-acetyl transferase]]
|-
| Acetoacetyl coenzyme A converts into [[β-hydroxybutyryl CoA]] || [[β-hydroxybutyryl-CoA dehydrogenase]]
|-
| β-hydroxybutyryl CoA converts into [[crotonyl CoA]] || [[crotonase]]
|-
| Crotonyl CoA converts into [[butyryl CoA]] ({{chem2|CH3CH2CH2C\dO\sCoA}}) || [[butyryl CoA dehydrogenase]]
|-
| A [[phosphate]] group replaces CoA to form [[butyryl phosphate]] || [[phosphobutyrylase]]
|-
| The phosphate group joins [[adenosine diphosphate|ADP]] to form [[adenosine triphosphate|ATP]] and [[butyrate]] || [[butyrate kinase]]
|}

Several species form [[acetone]] and [[n-Butanol|''n''-butanol]] in an alternative pathway, which starts as butyrate fermentation. Some of these species are:
* ''[[Clostridium acetobutylicum]]'', the most prominent acetone and butanol producer, used also in industry
* ''[[Clostridium beijerinckii]]''
* ''[[Clostridium tetanomorphum]]''
* ''[[Clostridium aurantibutyricum]]''

These bacteria begin with butyrate fermentation, as described above, but, when the [[pH]] drops below 5, they switch into butanol and acetone production to prevent further lowering of the pH. Two molecules of butanol are formed for each molecule of acetone.

The change in the pathway occurs after acetoacetyl CoA formation. This intermediate then takes two possible pathways:
* acetoacetyl CoA → acetoacetate → acetone
* acetoacetyl CoA → butyryl CoA → butyraldehyde → butanol

For commercial purposes Clostridium species are used preferably for butyric acid or butanol production.
The most common species used for probiotics is the [[Clostridium butyricum]].<ref>{{Cite journal |last1=Zigová |first1=Jana |last2=Šturdı́k |first2=Ernest |last3=Vandák |first3=Dušan |last4=Schlosser |first4=Štefan |date=October 1999 |title=Butyric acid production by Clostridium butyricum with integrated extraction and pertraction |url=https://linkinghub.elsevier.com/retrieve/pii/S0032959299000072 |journal=Process Biochemistry |language=en |volume=34 |issue=8 |pages=835–843 |doi=10.1016/S0032-9592(99)00007-2|url-access=subscription }}</ref>

===Fermentable fiber sources===
Highly-fermentable fiber residues, such as those from [[resistant starch]], [[oat bran]], [[pectin]], and [[guar]] are transformed by [[gut flora|colonic bacteria]] into [[short-chain fatty acid]]s (SCFA) including butyrate, producing more SCFA than less fermentable fibers such as [[cellulose]]s.<ref name=morrison/><ref name="lupton">{{cite journal | vauthors = Lupton JR | title = Microbial degradation products influence colon cancer risk: the butyrate controversy | journal = The Journal of Nutrition | volume = 134 | issue = 2 | pages = 479–482 | date = February 2004 | pmid = 14747692 | doi=10.1093/jn/134.2.479| doi-access = free}}</ref> One study found that resistant starch consistently produces more butyrate than other types of [[dietary fiber]].<ref>{{cite journal | vauthors = Cummings JH, Macfarlane GT, Englyst HN | title = Prebiotic digestion and fermentation | journal = The American Journal of Clinical Nutrition | volume = 73 | issue = 2 Suppl | pages = 415S–420S | date = February 2001 | pmid = 11157351 | doi = 10.1093/ajcn/73.2.415s | doi-access = free}}</ref> The production of SCFA from fibers in [[ruminant]] animals such as cattle is responsible for the butyrate content of milk and butter.<ref>{{cite journal | vauthors = Grummer RR | title = Effect of feed on the composition of milk fat | journal = Journal of Dairy Science | volume = 74 | issue = 9 | pages = 3244–3257 | date = September 1991 | pmid = 1779073 | doi = 10.3168/jds.S0022-0302(91)78510-X | doi-access = free }}</ref>

[[Fructans]] are another source of prebiotic soluble dietary fibers which can be digested to produce butyrate.<ref name="pmc4923077">{{cite journal |doi=10.3389/fmicb.2016.00979 |title=Bifidobacteria and Butyrate-Producing Colon Bacteria: Importance and Strategies for Their Stimulation in the Human Gut |year=2016 |last1=Rivière |first1=Audrey |last2=Selak |first2=Marija |last3=Lantin |first3=David |last4=Leroy |first4=Frédéric |last5=De Vuyst |first5=Luc |journal=Frontiers in Microbiology |volume=7 |page=979 |pmid=27446020 |pmc=4923077 |doi-access=free }}</ref> They are often found in the soluble fibers of foods which are high in [[Low-sulfur diet|sulfur]], such as the [[allium]] and [[cruciferous vegetables]]. [[Fructan#Fructan content of various foods|Sources of fructans]] include [[wheat]] (although some wheat strains such as [[spelt]] contain lower amounts),<ref>{{cite web|url=http://www.med.monash.edu/cecs/gastro/fodmap/diet-and-ibs.html#5|title=Frequently asked questions in the area of diet and IBS|publisher=Department of Gastroenterology Translational Nutrition Science, Monash University, Victoria, Australia |access-date=24 March 2016}}</ref> [[rye]], [[barley]], [[onion]], [[garlic]], [[Jerusalem artichoke|Jerusalem]] and [[globe artichoke]], [[asparagus]], [[beetroot]], [[chicory]], [[Dandelion|dandelion leaves]], [[leek]], [[radicchio]], the white part of [[spring onion]], [[broccoli]], [[brussels sprouts]], [[cabbage]], [[fennel]], and [[Prebiotic (nutrition)|prebiotics]], such as fructooligosaccharides ([[Fructooligosaccharide|FOS]]), [[oligofructose]], and [[inulin]].<ref>{{Cite journal|last1=Gibson|first1=Peter R.|last2=Shepherd|first2=Susan J.|date=1 February 2010|title=Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach|journal=Journal of Gastroenterology and Hepatology|volume=25|issue=2|pages=252–258|doi=10.1111/j.1440-1746.2009.06149.x|issn=1440-1746|pmid=20136989|s2cid=20666740|doi-access=free}}</ref><ref>{{Cite journal|last1=Gibson|first1=Peter R.|last2=Varney|first2=Jane|last3=Malakar|first3=Sreepurna|last4=Muir|first4=Jane G.|date=1 May 2015|title=Food components and irritable bowel syndrome|journal=Gastroenterology|volume=148|issue=6|pages=1158–1174.e4|doi=10.1053/j.gastro.2015.02.005|issn=1528-0012|pmid=25680668|doi-access=free}}</ref>

==Chemical reactions==
Butyric acid reacts as a typical carboxylic acid: it can form [[Butyramide|amide]], [[ester]], [[Butyric anhydride|anhydride]], and [[acyl chloride|chloride]] derivatives.<ref>{{cite book |doi=10.1039/9781847556196-00096 |chapter=Carboxylic acids and derivatives |title=General and Synthetic Methods |year=1985 |last1=Jenkins |first1=P. R. |volume=7 |pages=96–160 |isbn=978-0-85186-884-4}}</ref> The latter, [[butyryl chloride]], is commonly used as the intermediate to obtain the others.

==Uses==
Butyric acid is used in the preparation of various butyrate esters. It is used to produce [[cellulose acetate butyrate]] (CAB), which is used in a wide variety of tools, paints, and coatings, and is more resistant to degradation than [[cellulose acetate]].<ref>{{cite book|last1=Lokensgard|first1=Erik|title=Industrial Plastics: Theory and Applications|date=2015|publisher=Cengage Learning|edition=6th}}{{ISBN?}}{{page needed|date=May 2025}}</ref> CAB can degrade with exposure to heat and moisture, releasing butyric acid.<ref>{{cite news|last1=Williams|first1=R. Scott|title=Care of Plastics: Malignant plastics|volume=24|url=http://cool.conservation-us.org/waac/wn/wn24/wn24-1/wn24-102.html|access-date=29 May 2017|work=WAAC Newsletter|issue=1|publisher=Conservation OnLine}}</ref>

Low-molecular-weight esters of butyric acid, such as [[methyl butyrate]], have mostly pleasant aromas or tastes.<ref name=Ullmann/> As a consequence, they are used as food and perfume additives. It is an approved food flavoring in the EU [[FLAVIS database]] (number 08.005).

Due to its powerful odor, it has also been used as a fishing bait additive.<ref>[http://www.nutrabaits.net/freezer.html Freezer Baits] {{Webarchive|url=https://web.archive.org/web/20100125054429/http://www.nutrabaits.net/freezer.html |date=25 January 2010 }}, nutrabaits.net</ref> Many of the commercially available flavors used in [[Common carp|carp]] (''Cyprinus carpio'') baits use butyric acid as their ester base. It is not clear whether fish are attracted by the butyric acid itself or the substances added to it. Butyric acid was one of the few organic acids shown to be palatable for both [[tench]] and [[bitterling]].<ref>{{Cite journal | doi = 10.1046/j.1467-2979.2003.00121.x | last1 = Kasumyan | first1 = A.O. | last2 = Døving | first2 = K.B. | year = 2003 | title = Taste preferences in fishes | journal = Fish and Fisheries | volume = 4 | issue = 4| pages = 289–347 | bibcode = 2003AqFF....4..289K | name-list-style = vanc}}</ref>

The substance has been used as a [[stink bomb]] by the [[Sea Shepherd Conservation Society]] to disrupt Japanese [[whaling]] crews.<ref>[http://www.newser.com/story/80755/japanese-whalers-injured-by-acid-firing-activists.html Japanese Whalers Injured by Acid-Firing Activists] {{Webarchive|url=https://web.archive.org/web/20100608193257/http://www.newser.com/story/80755/japanese-whalers-injured-by-acid-firing-activists.html |date=8 June 2010 }}, newser.com, 10 February 2010</ref> The Dutch branch of [[Extinction Rebellion]] has used it as a chemical agent in a clothing store; several people who became unwell were treated on site by an ambulance crew.<ref>{{Cite web |date=2025-01-31 |title=Mensen onwel na actie Extinction Rebellion in kledingwinkel Naaldwijk |url=https://nos.nl/artikel/2554015-mensen-onwel-na-actie-extinction-rebellion-in-kledingwinkel-naaldwijk |access-date=2025-04-10 |website=nos.nl |language=nl}}</ref>

==Pharmacology==
{| class="wikitable" style="text-align:center; float:right"
|+ Human enzyme and GPCR binding<ref name="IUPHAR">{{cite web|title=Butyric acid|url=http://www.guidetopharmacology.org/GRAC/LigandDisplayForward?tab=biology&ligandId=1059|website=IUPHAR/BPS Guide to Pharmacology|publisher=International Union of Basic and Clinical Pharmacology|access-date=13 July 2018}}</ref><ref name="BindingDB">{{cite web|title=Butanoic acid and Sodium butyrate|url=http://www.bindingdb.org/bind/searchby_smiles.jsp?submit=Search&startPg=0&Increment=15&SearchType=3&smilesStr=CCCC%28%5BO-%5D%29%3DO&molfile=CCCC%28%5BO-%5D%29%3DO&Similarity=.99|website=BindingDB|publisher=The Binding Database|access-date=27 October 2020}}</ref>
! Inhibited enzyme !! [[IC50|IC<sub>50</sub>]] ({{abbr|nM|nanomolar}}) !! Entry note
|-
| [[HDAC1]] || 16,000 ||
|-
| [[HDAC2]] || 12,000 ||
|-
| [[HDAC3]] || 9,000 ||
|-
| [[HDAC4]] || 2,000,000 || Lower bound
|-
| [[HDAC5]] || 2,000,000 || Lower bound
|-
| [[HDAC6]] || 2,000,000 || Lower bound
|-
| [[HDAC7]] || 2,000,000 || Lower bound
|-
| [[HDAC8]] || 15,000 ||
|-
| [[HDAC9]] || 2,000,000 || Lower bound
|-
| [[Carbonic anhydrase I|CA1]] || 511,000 ||
|-
| [[Carbonic anhydrase I|CA2]] || 1,032,000 ||
|-
! [[GPCR]] target !! [[pEC50|pEC<sub>50</sub>]] !! Entry note
|-
| [[FFAR2]] || 2.9–4.6 || Full agonist
|-
| [[FFAR3]] || 3.8–4.9 || Full agonist
|-
| [[Hydroxycarboxylic acid receptor 2|{{chem2|HCA2}}]] || 2.8 || Agonist
|}

===Pharmacodynamics===
Butyric acid (pK<sub>a</sub> 4.82) is fully [[Ionization|ionized]] at [[physiological pH]], so its [[anion]] is the material that is mainly relevant in biological systems.
It is one of two primary [[endogenous agonist]]s of human [[hydroxycarboxylic acid receptor&nbsp;2]] ({{chem2|HCA2}}, also known as GPR109A), a {{nowrap|[[Gi alpha subunit|G<sub>i/o</sub>-coupled]]}} [[G protein-coupled receptor]] (GPCR),<ref name="IUPHAR's comprehensive 2011 review on HCARs" /><ref name="IUPHAR-DB HCAR family page" />

Like other [[short-chain fatty acid]]s (SCFAs), butyrate is an agonist at the [[free fatty acid receptor]]s [[FFAR2]] and [[FFAR3]], which function as nutrient sensors that facilitate the [[homeostatic control of energy balance]]; however, among the group of SCFAs, only butyrate is an agonist of [[hydroxycarboxylic acid receptor&nbsp;2|HCA<sub>2</sub>]].<ref name="Review – General summary as of April 2015" /><ref name="Butyrate pharmacodynamics and neuroepigenetic effects 2016 review">{{cite journal | vauthors = Bourassa MW, Alim I, Bultman SJ, Ratan RR | title = Butyrate, neuroepigenetics and the gut microbiome: Can a high fiber diet improve brain health? | journal = Neurosci. Lett. | volume = 625 | pages = 56–63 | date = June 2016 | pmid = 26868600 | pmc = 4903954 | doi = 10.1016/j.neulet.2016.02.009 }}</ref> It is also an [[HDAC inhibitor]] (specifically, HDAC1, HDAC2, HDAC3, and HDAC8),<ref name="IUPHAR" /><ref name="BindingDB" /> a drug that inhibits the function of [[histone deacetylase]] enzymes, thereby favoring an acetylated state of [[histone]]s in cells.<ref name="Butyrate pharmacodynamics and neuroepigenetic effects 2016 review" />

===Pharmacokinetics===
Butyrate that is produced in the colon through microbial fermentation of dietary fiber is primarily absorbed and metabolized by [[colonocytes]] and the liver{{#tag:ref|Most of the butyrate that is absorbed into [[blood plasma]] from the colon enters the circulatory system via the [[portal vein]]; most of the butyrate that enters the circulatory system by this route is taken up by the liver.<ref name="Butyrate pharmacodynamics and neuroepigenetic effects 2016 review" />|group="note"}} for the generation of ATP during energy metabolism; however, some butyrate is absorbed in the distal colon, which is not connected to the portal vein, thereby allowing for the [[distribution (pharmacology)|systemic distribution]] of butyrate to multiple organ systems through the circulatory system.<ref name="Butyrate pharmacodynamics and neuroepigenetic effects 2016 review" /><ref>{{cite journal |last1=van Hoogdalem |first1=Edward |last2=de Boer |first2=Albertus G. |last3=Breimer |first3=Douwe D. |title=Pharmacokinetics of rectal drug administration, Part I. General considerations and clinical applications of centrally acting drugs |journal=Clinical Pharmacokinetics |date=July 1991 |volume=21 |issue=1 |page=14 |doi=10.2165/00003088-199121010-00002 |pmid=1717195 |issn=0312-5963 |quote=the middle and inferior rectal veins drain the lower part of the rectum and venous blood is returned to the inferior vena cava. Therefore, drugs absorbed in the latter system will be delivered preferentially to the systemic circulation, bypassing the liver and avoiding first-pass metabolism}}</ref> Butyrate that has reached systemic circulation can readily cross the [[blood–brain barrier]] via [[monocarboxylate transporter]]s (i.e., certain members of the [[Solute carrier family#Families|SLC16A group of transporters]]).<ref name="SCFA MCT-mediated BBB passage – 2005 review">{{cite journal | vauthors = Tsuji A | title = Small molecular drug transfer across the blood–brain barrier via carrier-mediated transport systems | journal = NeuroRx | volume = 2 | issue = 1 | pages = 54–62 | year = 2005 | pmid = 15717057 | pmc = 539320 | doi = 10.1602/neurorx.2.1.54 | quote = Other in vivo studies in our laboratories indicated that several compounds including acetate, propionate, butyrate, benzoic acid, salicylic acid, nicotinic acid, and some β-lactam antibiotics may be transported by the MCT at the BBB.<sup>21</sup>&nbsp;... Uptake of valproic acid was reduced in the presence of medium-chain fatty acids such as hexanoate, octanoate, and decanoate, but not propionate or butyrate, indicating that valproic acid is taken up into the brain via a transport system for medium-chain fatty acids, not short-chain fatty acids.}}</ref><ref name="SCFA MCT-mediated BBB passage – 2014 review">{{cite journal | vauthors = Vijay N, Morris ME | title = Role of monocarboxylate transporters in drug delivery to the brain | journal = Curr. Pharm. Des. | volume = 20 | issue = 10 | pages = 1487–1498 | year = 2014 | pmid = 23789956 | pmc = 4084603 | doi = 10.2174/13816128113199990462| quote = Monocarboxylate transporters (MCTs) are known to mediate the transport of short chain monocarboxylates such as lactate, pyruvate and butyrate.&nbsp;... MCT1 and MCT4 have also been associated with the transport of short chain fatty acids such as acetate and formate which are then metabolized in the astrocytes [78].&nbsp;... SLC5A8 is expressed in normal colon tissue, and it functions as a tumor suppressor in human colon with silencing of this gene occurring in colon carcinoma. This transporter is involved in the concentrative uptake of butyrate and pyruvate produced as a product of fermentation by colonic bacteria. }}</ref> Other transporters that mediate the passage of butyrate across lipid membranes include [[SLC5A8]] (SMCT1), [[SLC27A1]] (FATP1), and [[SLC27A4]] (FATP4).<ref name="IUPHAR" /><ref name="SCFA MCT-mediated BBB passage – 2014 review" />

===Metabolism {{anchor|Butanoate metabolism}}===
Butyric acid is metabolized by various human [[XM-ligase]]s (ACSM1, ACSM2B, ASCM3, ACSM4, ACSM5, and ACSM6), also known as butyrate–CoA ligase.<ref name="HMDB">{{cite web|title=Butyric acid|url=http://www.hmdb.ca/metabolites/HMDB00039|website=Human Metabolome Database|publisher=University of Alberta|access-date=15 August 2015}}</ref><ref name="Butyrate metabolism">{{cite web|title=Butanoate metabolism – Reference pathway|url=http://www.genome.jp/kegg-bin/show_pathway?map00650|website=Kyoto Encyclopedia of Genes and Genomes|publisher=Kanehisa Laboratories|date=1 November 2017|access-date=1 February 2018}}</ref> The metabolite produced by this reaction is [[butyryl–CoA]], and is produced as follows:<ref name="HMDB" />

{{block indent|Adenosine triphosphate + butyric acid + coenzyme A → adenosine monophosphate + pyrophosphate + butyryl-CoA}}

As a [[short-chain fatty acid]], butyrate is metabolized by [[Mitochondrion|mitochondria]] as an energy (i.e., [[adenosine triphosphate]] or ATP) source through [[fatty acid metabolism]].<ref name="Butyrate pharmacodynamics and neuroepigenetic effects 2016 review" /> In particular, it is an important energy source for cells lining the mammalian [[colon (anatomy)|colon]] (colonocytes).<ref name=pmc4923077/> Without butyrates, colon cells undergo [[autophagy]] (i.e., self-digestion) and die.<ref>{{Cite journal|last1=Donohoe|first1=Dallas R.|last2=Garge|first2=Nikhil|last3=Zhang|first3=Xinxin|last4=Sun|first4=Wei|last5=O'Connell|first5=Thomas M.|last6=Bunger|first6=Maureen K.|last7=Bultman|first7=Scott J.|date=4 May 2011|title=The Microbiome and Butyrate Regulate Energy Metabolism and Autophagy in the Mammalian Colon|journal=Cell Metabolism|volume=13|issue=5|pages=517–526|doi=10.1016/j.cmet.2011.02.018|issn=1550-4131|pmc=3099420|pmid=21531334}}</ref>

In humans, the butyrate precursor [[tributyrin]], which is naturally present in butter, is metabolized by [[triacylglycerol lipase]] into [[dibutyrin]] and butyrate through the reaction:<ref name="BRENDA tributyrin">{{cite web| title=triacylglycerol lipase – Homo sapiens| url=http://www.brenda-enzymes.org/enzyme.php?ecno=3.1.1.3&Suchword=&organism%5B%5D=Homo+sapiens&show_tm=0| work=BRENDA| publisher=Technische Universität Braunschweig.| access-date=25 May 2015}}</ref>

{{block indent|Tributyrin + {{chem2|H2O →}} dibutyrin + butyric acid}}
{{clear right}}

==Biochemistry==
Butyrate has numerous effects on [[energy homeostasis]] in humans. These effects occur through its metabolism by mitochondria to generate {{abbr|ATP|adenosine triphosphate}} during [[fatty acid metabolism]] or through one or more of its [[histone-modifying enzyme]] targets (i.e., the [[Histone deacetylase#Classes of HDACs in higher eukaryotes|class I histone deacetylase]]s) and [[G-protein coupled receptor]] targets (i.e., [[FFAR2]], [[FFAR3]], and [[Hydroxycarboxylic acid receptor 2|{{chem2|HCA2}}]]).<ref name="Review – General summary as of April 2015">{{cite journal | vauthors = Kasubuchi M, Hasegawa S, Hiramatsu T, Ichimura A, Kimura I | title = Dietary gut microbial metabolites, short-chain fatty acids, and host metabolic regulation | journal = Nutrients | volume = 7 | issue = 4 | pages = 2839–2849 | year = 2015 | pmid = 25875123 | pmc = 4425176 | doi = 10.3390/nu7042839 | quote = Short-chain fatty acids (SCFAs) such as acetate, butyrate, and propionate, which are produced by gut microbial fermentation of dietary fiber, are recognized as essential host energy sources and act as signal transduction molecules via G-protein coupled receptors (FFAR2, FFAR3, OLFR78, GPR109A) and as epigenetic regulators of gene expression by the inhibition of histone deacetylase (HDAC). Recent evidence suggests that dietary fiber and the gut microbial-derived SCFAs exert multiple beneficial effects on the host energy metabolism not only by improving the intestinal environment, but also by directly affecting various host peripheral tissues.| doi-access = free }}</ref><ref name="Review for diabetes">{{cite journal | vauthors = Tilg H, Moschen AR | title = Microbiota and diabetes: an evolving relationship | journal = Gut | volume = 63 | issue = 9 | pages = 1513–1521 | date = September 2014 | pmid = 24833634 | doi = 10.1136/gutjnl-2014-306928| s2cid = 22633025 }}</ref>

===Mammalian gut===
Butyrate is essential to host immune homeostasis.<ref name="Review – General summary as of April 2015" /> Although the role and importance of butyrate in the gut is not fully understood, many researchers argue that a depletion of butyrate-producing bacteria in patients with several vasculitic conditions is essential to the pathogenesis of these disorders. A depletion of butyrate in the gut is typically caused by an absence or depletion of butyrate-producing-bacteria (BPB). This depletion in BPB leads to microbial [[dysbiosis]]. This is characterized by an overall low biodiversity and a depletion of key butyrate-producing members. Butyrate is an essential microbial metabolite with a vital role as a modulator of proper immune function in the host. It has been shown that children lacking in BPB are more susceptible to allergic disease<ref>{{cite journal| last1=Cait| first1= Alissa	| last2= Cardenas| first2= Erick| date=December 2019| title=Reduced genetic potential for butyrate fermentation in the gut microbiome of infants who develop allergic sensitization| journal= Journal of Allergy and Clinical Immunology| volume = 144| issue= 6| pages= 1638–1647. E3| doi= 10.1016/j.jaci.2019.06.029| pmid= 31279007 | doi-access= free}}</ref> and type 1 diabetes.<ref>{{cite journal|last1=Vatanen|first1=T.|last2=Franzosa|first2=E. A.|last3=Schwager|first3=R.|display-authors=et al|title=The human gut microbiome in early-onset type 1 diabetes from the TEDDY study|journal=Nature|volume=562|pages=589–594|date=2018|issue=7728|doi=10.1038/s41586-018-0620-2|pmid=30356183|pmc=6296767|bibcode= 2018Natur.562..589V|doi-access=free}}</ref> Butyrate is also reduced in a diet low in [[dietary fiber]], which can induce inflammation and have other adverse affects insofar as these [[short-chain fatty acid]]s activate [[Peroxisome proliferator-activated receptor gamma|PPAR-γ]].<ref name="pmid32623619">{{cite journal | vauthors=Kumar J, Rani K, Datt C | title=Molecular link between dietary fibre, gut microbiota and health | journal=[[Molecular Biology Reports]] | volume=47 | issue=8 | pages=6229–6237 | year=2020 | doi = 10.1007/s11033-020-05611-3 | pmid=32623619| s2cid=220337072 }}</ref> 

Decreased butyrate levels lead to a damaged or dysfunctional intestinal epithelial barrier.<ref>{{cite journal |last1=Ye |first1=Zi |last2=Zhang |first2=Ni |last3=Wu |first3=Chunyan |last4=Zhang |first4=Xinyuan |last5=Wang |first5=Qingfeng |last6=Huang |first6=Xinyue |last7=Du |first7=Liping |last8=Cao |first8=Qingfeng |last9=Tang |first9=Jihong |last10=Zhou |first10=Chunjiang |last11=Hou |first11=Shengping |last12=He |first12=Yue |last13=Xu |first13=Qian |last14=Xiong |first14=Xiao |last15=Kijlstra |first15=Aize |last16=Qin |first16=Nan |last17=Yang |first17=Peizeng |display-authors=6 |title=A metagenomic study of the gut microbiome in Behcet's disease |journal=Microbiome |date=4 August 2018 |volume=6 |issue=1 |pages=135 |doi=10.1186/s40168-018-0520-6 |pmid=30077182 |pmc=6091101 |doi-access=free }}</ref> Butyrate reduction has also been associated with ''[[Clostridioides difficile]]'' proliferation. Conversely, a high-fiber diet results in higher butyric acid concentration and inhibition of ''C. difficile'' growth.<ref>{{Cite journal |last1=Di Bella |first1=Stefano |last2=Sanson |first2=Gianfranco |last3=Monticelli |first3=Jacopo |last4=Zerbato |first4=Verena |last5=Principe |first5=Luigi |last6=Giuffrè |first6=Mauro |last7=Pipitone |first7=Giuseppe |last8=Luzzati |first8=Roberto |date=2024-02-29 |editor-last=Staley |editor-first=Christopher |others=Mayuresh Abhyankar |title=Clostridioides difficile infection: history, epidemiology, risk factors, prevention, clinical manifestations, treatment, and future options |journal=Clinical Microbiology Reviews |volume=37 |issue=2 |pages=e0013523 |language=en |doi=10.1128/cmr.00135-23 |pmid=38421181 |pmc=11324037 |issn=0893-8512}}</ref>

In the gut microbiomes found in the class Mammalia, omnivores and herbivores have butyrate-producing bacterial communities dominated by the butyryl-CoA:acetate CoA-transferase pathway, whereas carnivores have butyrate-producing bacterial communities dominated by the butyrate kinase pathway.<ref>{{cite journal|doi=10.1038/ismej.2014.179|title=Diet is a major factor governing the fecal butyrate-producing community structure across Mammalia, Aves and Reptilia |year=2015 |last1=Vital |first1=Marius |last2=Gao |first2=Jiarong |last3=Rizzo |first3=Mike |last4=Harrison |first4=Tara |last5=Tiedje |first5=James M. |journal=The ISME Journal |volume=9 |issue=4 |pages=832–843 |pmid=25343515 |pmc=4817703 |bibcode=2015ISMEJ...9..832V }}</ref>

The odor of butyric acid, which emanates from the sebaceous follicles of all mammals, works on [[ticks]] as a signal.

===Immunomodulation===
Butyrate's effects on the immune system are mediated through the inhibition of class I [[histone deacetylase]]s and activation of its [[G-protein coupled receptor]] targets: [[Hydroxycarboxylic acid receptor 2|{{chem2|HCA2}}]] (GPR109A), [[FFAR2]] (GPR43), and [[FFAR3]] (GPR41).<ref name="REVIEW butyrate human LL-37">{{cite journal |vauthors=Wang G |title=Human antimicrobial peptides and proteins |journal=Pharmaceuticals |volume=7 |issue=5 |pages=545–594 |year=2014 |pmid=24828484 |pmc=4035769 |doi=10.3390/ph7050545 |doi-access=free}}</ref>

===Colonocytes===
Responsible for about 70% of energy from the colonocytes, butyric acid is a critical SCFA in colon [[homeostasis]].<ref>{{cite journal |last1=Zeng |first1=Huawei |last2=Lazarova |first2=DL |last3=Bordonaro |first3=M |title=Mechanisms linking dietary fiber, gut microbiota and colon cancer prevention |journal=World Journal of Gastrointestinal Oncology |date=2014 |volume=6 |issue=2 |pages=41–51 |doi=10.4251/wjgo.v6.i2.41 |pmid=24567795 |pmc=3926973 |doi-access=free }}</ref> Short-chain fatty acids, which include butyric acid, are produced by beneficial [[Gut flora|colonic bacteria]] that feed on, or ferment prebiotics, supporting colonocytes by increasing energy conversion.<ref name="lupton"/>

==Butyrate salts and esters==
The butanoate [[ion]], {{chem2|C3H7COO-|auto=yes}}, is the [[conjugate base]] of butyric acid. It is the form found in biological systems at [[physiological pH]]. A butyric (or butanoic) compound is a [[carboxylate salt]] or [[ester]] of butyric acid.

===Examples===
====Salts====
* [[Sodium butyrate]]

====Esters====
* [[Butyl butyrate]]
* [[Butyryl-CoA]]
* [[Aircraft dope|Cellulose acetate butyrate]] (aircraft dope)
* [[Estradiol benzoate butyrate]]
* [[Ethyl butyrate]]
* [[Methyl butyrate]]
* [[Pentyl butyrate]]
* [[Tributyrin]]

==See also==
* [[List of saturated fatty acids]]
* [[Histone]]
** [[Histone-modifying enzyme]]
*** [[Histone acetylase]]
*** [[Histone deacetylase]]
* [[Hydroxybutyric acid]]s
** [[α-Hydroxybutyric acid]]
** [[β-Hydroxybutyric acid]]
** [[γ-Hydroxybutyric acid]]
* [[Oxobutyric acid]]s
** [[2-Oxobutyric acid]] (α-ketobutyric acid)
** [[3-Oxobutyric acid]] (acetoacetic acid)
** [[4-Oxobutyric acid]] (succinic semialdehyde)
* [[β-Methylbutyric acid]]
** [[β-Hydroxy β-methylbutyric acid]]

{{clear}}

==Notes==
{{reflist|group=note}}

==References==
{{EB1911|wstitle=Butyric Acid}}
{{reflist}}
{{reflist|group=Color legend}}

==External links==
{{Commons category|Butyric acid}}
* [https://webbook.nist.gov/cgi/cbook.cgi?Name=butanoic+acid&Units=SI NIST Standard Reference Data for butanoic acid]

{{Fatty acids}}
{{HDAC inhibitors}}
{{GABA metabolism and transport modulators}}
{{Authority control}}

[[Category:GABA analogues]]
[[Category:Flavors]]
[[Category:Alkanoic acids]]
[[Category:Fatty acids]]
[[Category:Foul-smelling chemicals]]
[[Category:Biomolecules]]
[[Category:Histone deacetylase inhibitors]]