Editing Propionic acid

{{short description|Carboxylic acid with chemical formula CH<sub>3</sub>CH<sub>2</sub>CO<sub>2</sub>H}}
{{Use dmy dates|date=February 2021}}
{{Chembox
| Name           = Propionic acid
| ImageFileL1    = Propionic_acid_chemical_structure.svg
| ImageSizeL1    = 100px
| ImageClassL1   = skin-invert
| ImageNameL1    = Simplified skeletal formula
| ImageFileR1    = Propionic_acid_flat_structure.png
| ImageSizeR1    = 100px
| ImageClassR1   = skin-invert
| ImageNameR1    = Full structural formula
| ImageFileL2    = Propionic-acid-3D-balls.png
| ImageSizeL2    = 100px
| ImageNameL2    = Ball-and-stick model
| ImageFileR2    = Propionic acid spheres.png
| ImageSizeR2    = 100px
| ImageNameR2    = Space-filling model
| ImageFile3     = Propionic acid.jpg
| ImageSize3     = 200px
| PIN            = Propanoic acid <!-- Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) -->
| OtherNames     = Carboxyethane<br />Ethanecarboxylic acid<br />Ethylformic acid<br />Metacetonic acid<br />Methylacetic acid<br />C3:0 ([[Fatty acid#Nomenclature|Lipid numbers]])
| Section1       = {{Chembox Identifiers
| index_label    = Propionic acid
| index1_label   = Propionate
| IUPHAR_ligand = 1062
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank = DB03766
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 30768
| SMILES = CCC(=O)O
| EINECS =   201-176-3
| CASNo = 79-09-4
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = JHU490RVYR
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 14021
| PubChem = 1032
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 1005
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C3H6O2/c1-2-3(4)5/h2H2,1H3,(H,4,5)
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = XBDQKXXYIPTUBI-UHFFFAOYSA-N
| RTECS = UE5950000
| CASNo1 = 72-03-7
| CASNo1_Ref = {{cascite|correct|CAS}}
| UNII1 = AKW5EM890C
| UNII1_Ref = {{fdacite|correct|FDA}}
| SMILES1 = CCC(=O)[O-]
| PubChem1 = 104745
| ChemSpiderID1 = 94556
 }}
| Section2       = {{Chembox Properties
| C=3 | H=6 | O=2
| Appearance = Colorless, oily liquid<ref name=PGCH/>
| Odor = Pungent, rancid, unpleasant<ref name=PGCH/>
| Density = 0.98797 g/cm<sup>3</sup><ref name=cons3 />
| Solubility = 8.19 g/g (−28.3&nbsp;°C)<br /> 34.97 g/g (−23.9&nbsp;°C)<br /> Miscible (≥ −19.3&nbsp;°C)<ref name=sioc>{{cite book|last1 = Seidell|first1 = Atherton|last2 = Linke|first2 = William F.|year = 1919|title = Solubilities of Inorganic and Organic Compounds|url = https://archive.org/details/solubilitiesino01seidgoog|publisher = D. Van Nostrand Company|edition = 2nd|page = 569}}</ref>
| SolubleOther = Miscible in [[Ethanol|EtOH]], [[Diethyl ether|ether]], [[Chloroform|{{chem|CHCl|3}}]]<ref name=chemister>{{Cite web |url=http://chemister.ru/Database/properties-en.php?dbid=1&id=1485 |title=chemister.ru (archived copy) |access-date=13 June 2014 |archive-url=https://web.archive.org/web/20161009114215/http://chemister.ru/Database/properties-en.php?dbid=1&id=1485 |archive-date=9 October 2016 |url-status=dead }}</ref>
| MeltingPtC = −20.5
| MeltingPt_ref =<ref name=crc>{{CRC90}}</ref>
| BoilingPtC = 141.15
| BoilingPt_ref =<ref name=crc />
| pKa = 4.88<ref name=pubchem />
| Viscosity = 1.175 c[[Poise (unit)|P]] (15&nbsp;°C)<ref name=cons3 /><br /> 1.02 cP (25&nbsp;°C)<br /> 0.668 cP (60&nbsp;°C)<br /> 0.495 cP (90&nbsp;°C)<ref name=pubchem>{{PubChemLink|1032}}</ref>
| RefractIndex = 1.3843<ref name=cons3>{{cite book|editor-last = Lagowski|editor-first = J.J.|year = 2012|title = The Chemistry of Nonaqueous Solvents|publisher = Elsevier|page = 362|volume = III|url = https://books.google.com/books?id=bXUSMbnCjhUC&pg=PA362|isbn = 978-0323151030}}</ref>
| SublimationConditions = Sublimes at −48&nbsp;°C<br /> Δ<sub>subl</sub>''H''<sup><s>o</s></sup> = 74 kJ/mol<ref name=nist />
| VaporPressure = 0.32 kPa (20&nbsp;°C)<ref name="sigma" /><br /> 0.47 kPa (25&nbsp;°C)<ref name=pubchem /><br /> 9.62 kPa (100&nbsp;°C)<ref name=nist />
| HenryConstant = 4.45·10<sup>−4</sup> L·atm/mol<ref name=pubchem />
| LogP = 0.33<ref name=pubchem />
| MagSus = −43.50·10<sup>−6</sup> cm<sup>3</sup>/mol
 }}
| Section3       = {{Chembox Structure
| Dipole = 0.63 [[Debye|D]] (22&nbsp;°C)<ref name=cons3 />
| CrystalStruct = [[monoclinic crystal system|Monoclinic]] (−95&nbsp;°C)<ref name=csba>{{Cite journal | doi = 10.1107/S0365110X62003278| title = The crystal structure of propionic acid| journal = Acta Crystallographica| volume = 15| issue = 12| pages = 1233–1239| year = 1962| last1 = Strieter | first1 = F. J.| last2 = Templeton | first2 = D. H.| last3 = Scheuerman | first3 = R. F.| last4 = Sass | first4 = R. L.| bibcode = 1962AcCry..15.1233S| url = http://www.escholarship.org/uc/item/55b9n7jj}}</ref>
| SpaceGroup = P2<sub>1</sub>/c<ref name=csba />
| LattConst_a = 4.04&nbsp;Å
| LattConst_b = 9.06&nbsp;Å
| LattConst_c = 11&nbsp;Å<ref name=csba />
| LattConst_alpha =
| LattConst_beta = 91.25
| LattConst_gamma =
 }}
| Section4       = {{Chembox Thermochemistry
| DeltaHf = −510.8 kJ/mol<ref name=nist>{{nist|name=Propanoic acid| id= C79094|accessdate=13 June 2014|mask=FFFF|units=SI}}</ref>
| DeltaHc = 1527.3 kJ/mol<ref name=cons3 /><ref name=nist />
| HeatCapacity = 152.8 J/mol·K<ref name=chemister /><ref name=nist />
| Entropy = 191 J/mol·K<ref name=nist />
 }}
| Section7       = {{Chembox Hazards
| GHSPictograms = {{GHS02}}{{GHS05}}{{GHS07}}
| GHS_ref=<ref name="sigma">{{Sigma-Aldrich| id= w292400|name=Propionic acid|accessdate=13 June 2014}}</ref>
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|314}}<ref name="sigma" />
| PPhrases = {{P-phrases|280|305+351+338|310}}<ref name="sigma" />
| MainHazards = Corrosive
| NFPA-H = 3
| NFPA-F = 2
| NFPA-R = 0
| FlashPtC = 54
| FlashPt_ref =<ref name="sigma" />
| AutoignitionPtC = 512
| LD50 = 1370 mg/kg (mouse, oral)<ref name=chemister />
| PEL = none<ref name=PGCH>{{PGCH|0529}}</ref>
| IDLH = N.D.<ref name=PGCH/>
| REL = TWA 10 ppm (30 mg/m<sup>3</sup>) ST 15 ppm (45 mg/m<sup>3</sup>)<ref name=PGCH/>
 }}
| Section8       = {{Chembox Related
| OtherAnions =
| OtherFunction_label = [[Carboxylic acid]]s
| OtherFunction = [[Acetic acid]]<br /> [[Lactic acid]]<br /> [[3-Hydroxypropionic acid]]<br /> [[Tartronic acid]]<br /> [[Acrylic acid]]<br /> [[Butyric acid]]
| OtherCompounds = [[1-Propanol]]<br /> [[Propionaldehyde]]<br /> [[Sodium propionate]]<br /> [[Propionic anhydride]]}}
}}

'''Propionic acid''' ({{IPAc-en|p|r|oʊ|p|i|ˈ|ɒ|n|ɪ|k}}, from the [[Greek language|Greek]] words πρῶτος : ''prōtos'', meaning "first", and πίων : ''píōn'', meaning "fat"; also known as '''propanoic acid''') is a naturally occurring [[carboxylic acid]] with [[chemical formula]] {{chem|CH|3|CH|2|CO|2|H}}. It is a liquid with a pungent and unpleasant smell somewhat resembling [[body odor]]. The [[anion]] {{chem|CH|3|CH|2|CO|2|-}} as well as the [[Carboxylate salt|salts]] and [[ester]]s of propionic acid are known as '''propionates''' or '''propanoates'''.

About half of the world production of propionic acid is consumed as a [[preservative]] for both animal feed and food for human consumption. It is also useful as an intermediate in the production of other chemicals, especially polymers.

==History==
Propionic acid was first described in 1844 by [[Johann Gottlieb]], who found it among the degradation products of sugar.<ref>Johann Gottlieb (1844) [https://babel.hathitrust.org/cgi/pt?id=uva.x002457921;view=1up;seq=581 "Ueber die Einwirkung von schmelzendem Kalihydrat auf Rohrzucker, Gummi, Stärkmehl und Mannit"] (On the effect of molten potassium hydroxide on raw sugar, rubber, starch powder, and mannitol), ''Annalen der Chemie und Pharmacie'', '''52''' :  121–130.  After combining raw sugar with an excess of potassium hydroxide and distilling the result, Gottlieb obtained a product that he called "Metacetonsäure" (meta-acetone acid) on p. 122:  ''"Das Destillat ist stark sauer und enthält Ameisensäure, Essigsäure und eine neue Säure, welche ich, aus unten anzuführenden Gründen, Metacetonsäure nenne."''  (The distillate is strongly acidic and contains formic acid, acetic acid, and a new acid, which for reasons to be presented below I call "meta-acetone acid".)</ref> Over the next few years, other chemists produced propionic acid by different means, none of them realizing they were producing the same substance.  In 1847, French chemist [[Jean-Baptiste Dumas]] established all the acids to be the same compound, which he called propionic acid, from the [[Greek language|Greek]] words πρῶτος (prōtos), meaning ''first'', and πίων (piōn), meaning ''fat'', because it is the smallest {{chem|H(CH|2|)|n|COOH}} acid that exhibits the properties of the other [[fatty acid]]s, such as producing an oily layer when salted out of water and having a soapy [[potassium]] [[Potassium propionate|salt]].<ref>Dumas, Malaguti, and F. Leblanc (1847) [http://gallica.bnf.fr/ark:/12148/bpt6k2982c/f785.item.r=.zoom "Sur l'identité des acides métacétonique et butyro-acétique"] [On the identity of metacetonic acid and butyro-acetic acid], ''Comptes rendus'', '''25''' :  781–784.  Propionic acid is named on p. 783:  ''"Ces caractères nous ont conduits à désigner cet acide sous le nom d'''acide propionique'', nom qui rappelle sa place dans la séries des acides gras:  il en est le premier."'' (These characteristics led us to designate this acid by the name of ''propionic acid'', a name that recalls its place in the series of fatty acids:  it is the first of them.)</ref>

==Properties==
Propionic acid has physical properties intermediate between those of the smaller carboxylic acids, [[formic acid|formic]] and [[Acetic acid|acetic]] acids, and the larger [[fatty acid]]s.  It is miscible with water, but can be removed from water by adding salt.  As with acetic and formic acids, it consists of [[hydrogen bond]]ed pairs of molecules in both the liquid and the vapor.

Propionic acid displays the general properties of carboxylic acids: it can form [[amide]], [[ester]], [[acid anhydride|anhydride]], and [[acyl chloride|chloride]] derivatives.  It undergoes the [[Hell–Volhard–Zelinsky halogenation|Hell–Volhard–Zelinsky reaction]] that involves α-[[halogenation]] of a carboxylic acid with [[bromine]], [[catalyst|catalysed]] by [[phosphorus tribromide]], in this case to form [[2-bromopropanoic acid]], {{chem|CH|3|CHBrCOOH}}.<ref>{{OrgSynth | first1 = C. S. | last1 = Marvel | first2 = V. | last2 = du Vigneaud | title = α-Bromoisovaleric acid | volume = 11 | pages = 20 | collvol = 2 | collvolpages = 93 | year = 1931 | prep = cv2p0093 | doi = 10.15227/orgsyn.011.0020 }}</ref>  This product has been used to prepare a [[racemic mixture]] of [[alanine]] by [[Solvolysis#ammonolysis|ammonolysis]].<ref>{{cite journal|title = Synthesis of ''d'',''l''-Alanine in Improved Yield from α-Bromopropionic Acid and Aqueous Ammonia|first1 = Walter C.|last1 = Tobie|first2 = Gilbert B.|last2 = Ayres|journal = [[Journal of the American Chemical Society]]|year = 1937|volume = 59|issue = 5|page = 950|doi = 10.1021/ja01284a510|doi-access = free| bibcode=1937JAChS..59..950T }}</ref><ref>{{OrgSynth | first1 = Walter C. | last1 = Tobie | first2 = Gilbert B. | last2 = Ayres | title = ''dl''-Alanine | prep = cv1p0021 | year = 1941 | collvol = 1 | collvolpages = 21 | doi = 10.15227/orgsyn.009.0004 |doi-access = free}}</ref>
<!--- Note: This Org Synth manuscript is in two parts; the Kendall and McKenzie part was first published in 1929 (vol 9, p. 4) and deals with a Strecker synthesis of alanine.  The second part by Tobie and Ayres was first published in JACS in 1937 and appended to the Kendall and McKenzie Org Synth report in collvol 1 in 1941.  It is the second part that relates to preparing alanine from 2-bromopropanoic acid.  Please be careful if checking / changing these reference, which do share most citation details.  --->

::[[File:Preparation of alanine from propionic acid.png|500px|class=skin-invert-image]]

==Manufacture==
===Chemical===
In industry, propionic acid is mainly produced by the [[Carbonylation#Reppe chemistry|hydrocarboxylation]] of [[ethylene]] using [[nickel carbonyl]] as the catalyst:<ref name=Ullmann>{{Ullmann |year=2018 |first1=Ulf-Rainer |last1=Samel |first2=Walter |last2=Kohler |first3=Armin Otto |last3=Gamer |first4=Ullrich |last4=Keuser |first5=Shang-Tian |last5=Yang |first6=Ying |last6=Jin |first7=Meng |last7=Lin |first8=Zhongqiang |last8=Wang |first9=Joaquim Henrique |last9=Teles |title=Propionic Acid and Derivatives |doi=10.1002/14356007.a22_223.pub4}}</ref>

:[[File:Industrial synthesis of propionic acid (hydrocarboxylation process).svg|450px|class=skin-invert-image|Hydrocarboxylation of ethene with carbon monoxide and water to form propionic acid in the presence of nickel tetracarbonyl as catalyst]]

It is also produced by the aerobic [[oxidation]] of [[propionaldehyde]].  In the presence of [[cobalt]] or [[manganese]] salts (manganese propionate is most commonly used), this reaction proceeds rapidly at temperatures as mild as 40–50&nbsp;°C:

:[[File:Industrial synthesis of propionic acid (oxidation process).svg|450px|class=skin-invert-image|Liquid-phase oxidation of propionaldehyde with atmospheric oxygen to form propionic acid in the presence of manganese(II)-propionate as catalyst]]

Large amounts of propionic acid were once produced as a byproduct of acetic acid manufacture. At the current time, the world's largest producer of propionic acid is [[BASF]], with approximately 150 kt/a production capacity.

===Biotechnological <span class="anchor" id="Propionic acid fermentation"></span> ===
Biotechnological production of propionic acid mainly uses ''[[Propionibacterium]]'' strains.<ref>{{cite journal |doi=10.1007/s00253-017-8616-7 |title=Propionibacterium SPP.—source of propionic acid, vitamin B12, and other metabolites important for the industry |year=2018 |last1=Piwowarek |first1=Kamil |last2=Lipińska |first2=Edyta |last3=Hać-Szymańczuk |first3=Elżbieta |last4=Kieliszek |first4=Marek |last5=Ścibisz |first5=Iwona |journal=Applied Microbiology and Biotechnology |volume=102 |issue=2 |pages=515–538 |pmid=29167919 |pmc=5756557 |s2cid=23599974 }}</ref> However, large scale production of propionic acid by ''Propionibacteria'' faces challenges such as severe inhibition of end-products during cell growth and the formation of by-products (acetic acid and [[succinic acid]]).<ref>{{Cite journal|doi = 10.3109/07388551.2011.651428|pmid = 22299651|title = Microbial production of propionic acid from propionibacteria: Current state, challenges and perspectives|journal = Critical Reviews in Biotechnology|volume = 32|issue = 4|pages = 374–381|year = 2012|last1 = Liu|first1 = Long|last2 = Zhu|first2 = Yunfeng|last3 = Li|first3 = Jianghua|last4 = Wang|first4 = Miao|last5 = Lee|first5 = Pengsoon|last6 = Du|first6 = Guocheng|last7 = Chen|first7 = Jian|s2cid = 25823025}}</ref> One approach to improve productivity and yield during fermentation is through the use of cell immobilization techniques, which also promotes easy recovery, reuse of the cell biomass and enhances microorganisms' stress tolerance.<ref>{{cite journal | doi = 10.1007/s00253-015-6517-1| pmid = 25776062| title = A novel approach to monitor stress-induced physiological responses in immobilized microorganisms| journal = Applied Microbiology and Biotechnology| volume = 99| issue = 8| pages = 3573–3583| year = 2015| last1 = Alonso| first1 = Saúl| last2 = Rendueles| first2 = Manuel| last3 = Díaz| first3 = Mario| s2cid = 860853}}</ref> In 2018, 3D printing technology was used for the first time to create a matrix for cell immobilization in fermentation. Propionic acid production by ''Propionibacterium acidipropionici'' immobilized on 3D-printed nylon beads was chosen as a model study. It was shown that those 3D-printed beads were able to promote high density cell attachment and propionic acid production, which could be adapted to other fermentation bioprocesses.<ref>{{cite journal | doi = 10.1016/j.biortech.2017.10.087| pmid = 29136932| title = Cell immobilization on 3D-printed matrices: A model study on propionic acid fermentation| journal = Bioresource Technology| volume = 249| pages = 777–782| year = 2018| last1 = Belgrano| first1 = Fabricio dos Santos| last2 = Diegel| first2 = Olaf| last3 = Pereira| first3 = Nei| last4 = Hatti-Kaul| first4 = Rajni| bibcode = 2018BiTec.249..777B}}</ref> Other cell immobilization matrices have been tested, such as recycled-glass Poraver and fibrous-bed bioreactor.<ref>{{cite journal | doi = 10.1016/j.biortech.2012.05.079| pmid = 22728152| title = Batch- and continuous propionic acid production from glycerol using free and immobilized cells of Propionibacterium acidipropionici| journal = Bioresource Technology| volume = 118| pages = 553–562| year = 2012| last1 = Dishisha| first1 = Tarek| last2 = Alvarez| first2 = Maria Teresa| last3 = Hatti-Kaul| first3 = Rajni| bibcode = 2012BiTec.118..553D| s2cid = 29658955| url = http://lup.lub.lu.se/search/ws/files/4073436/4937831.pdf}}</ref><ref>{{cite journal | doi = 10.1002/bit.20473| pmid = 15977254| title = Enhanced propionic acid fermentation by ''Propionibacterium'' acidipropionici mutant obtained by adaptation in a fibrous-bed bioreactor| journal = Biotechnology and Bioengineering| volume = 91| issue = 3| pages = 325–337| year = 2005| last1 = Suwannakham| first1 = Supaporn| last2 = Yang| first2 = Shang-Tian}}</ref>

Alternative methods of production have been trialled, by genetically engineering strains of ''[[Escherichia coli]]'' to incorporate the necessary pathway, the Wood-Werkman cycle.<ref>{{cite journal |doi=10.1002/bit.27182 |title=Engineering Escherichia coli for propionic acid production through the Wood–Werkman cycle |year=2020 |last1=Gonzalez-Garcia |first1=Ricardo A. |last2=McCubbin |first2=Timothy |last3=Turner |first3=Mark S. |last4=Nielsen |first4=Lars K. |last5=Marcellin |first5=Esteban |journal=Biotechnology and Bioengineering |volume=117 |issue=1 |pages=167–183 |pmid=31556457 |s2cid=203438727 |doi-access=free }}</ref>

==Industrial uses==
Propionic acid inhibits the growth of [[Mold (fungus)|mold]] and some bacteria at levels between 0.1 and 1% by weight.  As a result, some propionic acid produced is consumed as a [[preservative]] for both animal feed and food for human consumption. For animal feed, it is used either directly or as its [[ammonium]] salt. This application accounts for about half of the world production of propionic acid. The antibiotic [[monensin]] is added to cattle feed to favor [[Propionibacterium|propionibacteria]] over acetic acid producers in the [[rumen]]; this produces less carbon dioxide and feed conversion is better. Another major application is as a preservative in baked goods, which use the [[sodium]] and [[calcium]] salts.<ref name=Ullmann/> As a [[food additive]], it is approved for use in the EU,<ref>{{cite web | url = http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist | title = Current EU approved additives and their E Numbers | publisher = UK Food Standards Agency | access-date=27 October 2011 }}</ref> US,<ref>{{ cite web | url = https://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/ucm191033.htm#ftnT | archive-url = https://web.archive.org/web/20100108135705/http://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/ucm191033.htm#ftnT | url-status = dead | archive-date = 8 January 2010 | title = Listing of Food Additives Status Part II | publisher = US Food and Drug Administration | access-date=27 October 2011 }}</ref> Australia and New Zealand.<ref>{{cite web | url = http://www.comlaw.gov.au/Details/F2011C00827 | title = Standard 1.2.4 – Labelling of ingredients | work = Australia New Zealand Food Standards Code | date = 8 September 2011 | publisher = Comlaw.au | access-date=27 October 2011 }}</ref>

Propionic acid is also useful as an intermediate in the production of other chemicals, especially polymers. [[Cellulose acetate|Cellulose-acetate-propionate]] is a useful [[thermoplastic]].  [[Vinyl propionate]] is also used.  In more specialized applications, it is also used to make [[pesticide]]s and [[pharmaceutical]]s.  The [[ester]]s of propionic acid have fruit-like odors and are sometimes used as [[solvent]]s or artificial flavorings.<ref name=Ullmann/>

In [[biogas plants]], propionic acid is a common intermediate product, which is formed by fermentation with propionic acid bacteria. Its degradation in anaerobic environments (e.g. biogas plants) requires the activity of complex microbial communities.<ref name="Ahlert">{{cite journal|last1 = Ahlert|first1 = Stephan|last2 = Zimmermann|first2 = Rita|last3 = Ebling|first3 = Johannes|last4 = König|first4 = Helmut|year = 2016|title = Analysis of propionate-degrading consortia from agricultural biogas plants|journal = MicrobiologyOpen |doi = 10.1002/mbo3.386|pmid = 27364538|pmc = 5221444|doi-access = free|volume = 5|issue = 6|pages = 1027–1037}}</ref>

In production of the [[Jarlsberg cheese]], a propionic acid bacterium is used to give both taste and holes.<ref>[https://www.jarlsberg.com/articles/qa www.jarlsberg.com] quote: " In the production of Jarlsberg®, propionic acid bacteria (the Secret Recipe!) is used to give the cheese its characteristic taste and holes."</ref>

==Biology==
Propionic acid is produced biologically as its coenzyme A ester, [[propionyl-CoA]], from the [[metabolism|metabolic]] breakdown of fatty acids containing [[odd number]]s of [[carbon]] atoms, and also from the breakdown of some [[amino acid]]s. Bacteria of the genus ''[[Propionibacterium]]'' produce propionic acid as the end-product of their [[anaerobic respiration|anaerobic]] metabolism.  This class of bacteria is commonly found in the stomachs of [[ruminant]]s and the [[Cutibacterium acnes|sweat glands of humans]], and their activity is partially responsible for the odor of [[Emmental cheese]], [[Swiss cheese (North America)|American "Swiss cheese"]] and [[sweat]].

The metabolism of propionic acid begins with its conversion to propionyl [[coenzyme A]], the usual first step in the metabolism of [[carboxylic acid]]s.  Since propionic acid has three carbons, propionyl-CoA cannot directly enter either [[beta oxidation]] or the [[citric acid cycle]]s.  In most [[vertebrate]]s, propionyl-CoA is [[carboxylation|carboxylated]] to <small>D</small>-[[methylmalonyl-CoA]], which is [[Isomerisation|isomerised]] to <small>L</small>-methylmalonyl-CoA. A [[vitamin B12|vitamin B<sub>12</sub>]]-dependent enzyme catalyzes rearrangement of <small>L</small>-methylmalonyl-CoA to [[succinyl-CoA]], which is an intermediate of the citric acid cycle and can be readily incorporated there.<ref>{{Cite book|last=Lehninger, Albert L.|url=https://www.worldcat.org/oclc/55476414|title=Lehninger principles of biochemistry|date=2005|publisher=W.H. Freeman|others=Nelson, David L. (David Lee), 1942-, Cox, Michael M.|isbn=0-7167-4339-6|edition=Fourth|location=New York|oclc=55476414}}</ref>

Propionic acid serves as a substrate for [[hepatic]] [[gluconeogenesis]] via conversion to succinyl-CoA.<ref>{{cite journal|last1=Aschenbach|first1=JR|last2=Kristensen|first2=NB|last3=Donkin|first3=SS|last4=Hammon|first4=HM|last5=Penner|first5=GB|date=December 2010|title=Gluconeogenesis in dairy cows: the secret of making sweet milk from sour dough.|journal=IUBMB Life|volume=62|issue=12|pages=869–77|doi=10.1002/iub.400|pmid=21171012|doi-access=free|s2cid=21117076}}</ref><ref>{{Cite journal|last1=Perry|first1=Rachel J.|last2=Borders|first2=Candace B.|last3=Cline|first3=Gary W.|last4=Zhang|first4=Xian-Man|last5=Alves|first5=Tiago C.|last6=Petersen|first6=Kitt Falk|last7=Rothman|first7=Douglas L.|last8=Kibbey|first8=Richard G.|last9=Shulman|first9=Gerald I.|date=21 March 2016|title=Propionate Increases Hepatic Pyruvate Cycling and Anaplerosis and Alters Mitochondrial Metabolism|journal=Journal of Biological Chemistry|volume=291|issue=23|pages=12161–12170|doi=10.1074/jbc.m116.720631|pmid=27002151|pmc=4933266|issn=0021-9258|doi-access=free}}</ref> Additionally, [[Exogeny|exogenous]] propionic acid administration results in more [[Endogeny (biology)|endogenous]] glucose production than can be accounted for by gluconeogenic conversion alone.<ref>{{Cite journal|last=Ringer|first=A. I.|date=2 August 1912|title=The Quantitative Conversion of Propionic Acid into Glucose|url=https://www.jbc.org/content/12/3/511.citation|journal=Journal of Biological Chemistry|volume=12|pages=511–515|doi=10.1016/S0021-9258(18)88686-0|doi-access=free}}</ref> Exogenous propionic acid may [[upregulate]] endogenous glucose production via increases in [[norepinephrine]] and [[glucagon]], suggesting that chronic ingestion of propionic acid may have adverse metabolic consequences.<ref>{{Cite journal|last1=Tirosh|first1=Amir|last2=Calay|first2=Ediz S.|last3=Tuncman|first3=Gurol|last4=Claiborn|first4=Kathryn C.|last5=Inouye|first5=Karen E.|last6=Eguchi|first6=Kosei|last7=Alcala|first7=Michael|last8=Rathaus|first8=Moran|last9=Hollander|first9=Kenneth S.|last10=Ron|first10=Idit|last11=Livne|first11=Rinat|date=24 April 2019|title=The short-chain fatty acid propionate increases glucagon and FABP4 production, impairing insulin action in mice and humans|journal=Science Translational Medicine|volume=11|issue=489|pages=eaav0120|doi=10.1126/scitranslmed.aav0120|pmid=31019023|issn=1946-6234|doi-access=free}}</ref>

In [[propionic acidemia]], a rare inherited genetic disorder, propionate acts as a metabolic toxin in liver cells by accumulating in mitochondria as propionyl-CoA and its derivative, methylcitrate, two tricarboxylic acid cycle inhibitors.  Propanoate is metabolized oxidatively by [[glia]], which suggests astrocytic vulnerability in propionic acidemia when intramitochondrial propionyl-CoA may accumulate. Propionic acidemia may alter both neuronal and glial gene expression by affecting histone acetylation.<ref name="macfabe">{{cite journal
|author1=D. F. MacFabe |author2=D. P. Cain |author3=K. Rodriguez-Capote |author4=A. E. Franklin |author5=J. E. Hoffman |author6=F. Boon |author7=A. R. Taylor |author8=M. Kavaliers |author9=K.-P. Ossenkopp | journal = Behavioural Brain Research | title = Neurobiological effects of intraventricular propionic acid in rats: Possible role of short-chain fatty acids on the pathogenesis and characteristics of autism spectrum disorders | year = 2007 | volume = 176 | issue = 1 | pages = 149–169 | doi = 10.1016/j.bbr.2006.07.025 |pmid=16950524 |s2cid=3054752 }}</ref><ref>{{cite journal |author1=N. H. T. Nguyen |author2=C. Morland |author3=S. Villa Gonzalez |author4=F. Rise |author5=J. Storm-Mathisen |author6=V. Gundersen |author7=B. Hassel | journal = Journal of Neurochemistry | title = Propionate increases neuronal histone acetylation, but is metabolized oxidatively by glia. Relevance for propionic acidemia | year = 2007 | volume = 101 | pmid = 17286595 | issue = 3 | pages = 806–814 | doi = 10.1111/j.1471-4159.2006.04397.x |s2cid=514557 |doi-access=free }}</ref>  When propionic acid is infused directly into rodents' brains, it produces reversible behavior (e.g., [[hyperactivity]], [[dystonia]], social impairment, [[perseveration]]) and brain changes (e.g., innate neuroinflammation, glutathione depletion) that may be used as a means to model [[autism]] in rats.<ref name="macfabe" />

===Human occurrence===
The human skin is host of several species of ''Propionibacteria''.  The most notable one is the ''[[Cutibacterium acnes]]'' (formerly known as ''Propionibacterium acnes''), which lives mainly in the [[sebaceous gland]]s of the skin and is one of the principal causes of [[acne]].<ref>{{cite journal |doi=10.1016/j.clindermatol.2004.03.005 |title=Acne and propionibacterium acnes |year=2004 |last1=Bojar |first1=Richard A. |last2=Holland |first2=Keith T. |journal=Clinics in Dermatology |volume=22 |issue=5 |pages=375–379 |pmid=15556721 }}</ref> Propionate is observed to be among the most common [[short-chain fatty acid]]s produced in the [[large intestine]] of humans by [[gut microbiome|gut microbiota]] in response to indigestible carbohydrates ([[dietary fiber]]) in the diet.<ref>{{cite journal |last1=Cani |first1=Patrice D. |last2=Knauf |first2=Claude |title=How gut microbes talk to organs: The role of endocrine and nervous routes |journal=Molecular Metabolism |date=27 May 2016 |volume=5 |issue=9 |pages=743–752 |doi=10.1016/j.molmet.2016.05.011 |pmid=27617197 |pmc=5004142 }}</ref><ref name = metab>{{cite journal|last1=den Besten |first1=G |last2=van Eunen |first2=K |last3=Groen |first3=AK |last4=Venema |first4=K|last5=Reijngoud|first5=DJ|last6=Bakker|first6=BM|title=The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism.|journal=Journal of Lipid Research|date=September 2013|volume=54|issue=9|pages=2325–40|doi=10.1194/jlr.R036012 |doi-access=free |pmid=23821742|pmc=3735932}}</ref> The role of the gut microbiota and their metabolites, including propionate, in mediating brain function has been reviewed.<ref>{{cite journal |doi=10.1038/mp.2016.50 |doi-access=free |title=From gut dysbiosis to altered brain function and mental illness: Mechanisms and pathways |year=2016 |last1=Rogers |first1=G. B. |last2=Keating |first2=D. J. |last3=Young |first3=R. L. |last4=Wong |first4=M-L |last5=Licinio |first5=J. |last6=Wesselingh |first6=S. |journal=Molecular Psychiatry |volume=21 |issue=6 |pages=738–748 |pmid=27090305 |pmc=4879184 |s2cid=18589882 }}</ref>

A study in mice suggests that propionate is produced by the bacteria of the genus ''[[Bacteroides]]'' in the gut, and that it offers some protection against ''[[Salmonella]]'' there.<ref>{{cite journal |doi=10.1016/j.chom.2018.07.002   |title=A Gut Commensal-Produced Metabolite Mediates Colonization Resistance to Salmonella Infection |year=2018 |last1=Jacobson |first1=Amanda |last2=Lam |first2=Lilian |last3=Rajendram |first3=Manohary |last4=Tamburini |first4=Fiona |last5=Honeycutt |first5=Jared |last6=Pham |first6=Trung |last7=Van Treuren |first7=Will |last8=Pruss |first8=Kali |last9=Stabler |first9=Stephen Russell |last10=Lugo |first10=Kyler |last11=Bouley |first11=Donna M. |last12=Vilches-Moure |first12=Jose G. |last13=Smith |first13=Mark |last14=Sonnenburg |first14=Justin L. |last15=Bhatt |first15=Ami S. |last16=Huang |first16=Kerwyn Casey |last17=Monack |first17=Denise |journal=Cell Host & Microbe |volume=24 |issue=2 |pages=296–307.e7 |pmid=30057174 |pmc=6223613 }}</ref> Another study finds that fatty acid propionate can calm the immune cells that drive up blood pressure, thereby protecting the body from damaging effects of high blood pressure.<ref>{{cite journal |doi=10.1161/CIRCULATIONAHA.118.036652 |title=Short-Chain Fatty Acid Propionate Protects from Hypertensive Cardiovascular Damage |year=2019 |last1=Bartolomaeus |first1=Hendrik |last2=Balogh |first2=András |last3=Yakoub |first3=Mina |last4=Homann |first4=Susanne |last5=Markó |first5=Lajos |last6=Höges |first6=Sascha |last7=Tsvetkov |first7=Dmitry |last8=Krannich |first8=Alexander |last9=Wundersitz |first9=Sebastian |last10=Avery |first10=Ellen G. |last11=Haase |first11=Nadine |last12=Kräker |first12=Kristin |last13=Hering |first13=Lydia |last14=Maase |first14=Martina |last15=Kusche-Vihrog |first15=Kristina |last16=Grandoch |first16=Maria |last17=Fielitz |first17=Jens |last18=Kempa |first18=Stefan |last19=Gollasch |first19=Maik |last20=Zhumadilov |first20=Zhaxybay |last21=Kozhakhmetov |first21=Samat |last22=Kushugulova |first22=Almagul |last23=Eckardt |first23=Kai-Uwe |last24=Dechend |first24=Ralf |last25=Rump |first25=Lars Christian |last26=Forslund |first26=Sofia K. |last27=Müller |first27=Dominik N. |last28=Stegbauer |first28=Johannes |last29=Wilck |first29=Nicola |journal=Circulation |volume=139 |issue=11 |pages=1407–1421 |pmid=30586752 |pmc=6416008 }}</ref>

=== Bacteriology ===
The Bacteria species ''[[Coprothermobacter platensis]]'' produces propionate when fermenting gelatin.<ref>{{Cite journal|last1=Etchebehere|first1=C.|last2=Pavan|first2=M. E.|last3=Zorzópulos|first3=J.|last4=Soubes|first4=M.|last5=Muxí|first5=L.|date=October 1998|title=Coprothermobacter platensis sp. nov., a new anaerobic proteolytic thermophilic bacterium isolated from an anaerobic mesophilic sludge|journal=International Journal of Systematic Bacteriology|volume=48 Pt 4|issue=4|pages=1297–1304|doi=10.1099/00207713-48-4-1297|issn=0020-7713|pmid=9828430|doi-access=free}}</ref> ''[[Prevotella brevis]]'' and ''Prevotella ruminicola'' also generate propionate when fermenting glucose.<ref>{{Cite web |last1=Zhang |first1=Bo |last2=Lingga |first2=Christopher |last3=De Groot |first3=Hannah |last4=Hackmann |first4=Timothy J |date=September 30, 2023 |title=The oxidoreductase activity of Rnf balances redox cofactors during fermentation of glucose to propionate in Prevotella |url=https://www.researchgate.net/publication/374334665 |access-date=September 26, 2024 |website=Research Gate}}</ref> 

== Propionate salts and esters ==
The '''propionate''' {{IPAc-en|'|p|r|oʊ|p|i|ə|n|eɪ|t}}, or '''propanoate''',  [[ion]] is {{chem|[[Carbon|C]]|2|[[Hydrogen|H]]|5|C[[Oxygen|O]]O|−}}, the [[conjugate base]] of propionic acid. It is the form found in biological systems at [[physiological pH]]. A propionic, or propanoic, compound is a [[carboxylate salt]] or [[ester]] of propionic acid. In these compounds, propionate is often written in shorthand, as {{chem|CH|3|CH|2|CO|2}} or simply {{chem|EtCO|2}}.

Propionates should not be confused with propenoates (commonly known as [[acrylate]]s), the ions/salts/esters of propenoic acid (also known as 2-propenoic acid or [[acrylic acid]]).

===Examples===
====Salts====
* [[Sodium propionate]] {{chem|NaC|2|H|5|CO|2}}
* [[Potassium propionate]] {{chem|KC|2|H|5|CO|2}}
* [[Calcium propionate]] {{chem|Ca(C|2|H|5|CO|2|)|2}}
* [[Zirconium propionate]] {{chem|Zr(C|2|H|5|CO|2|)|4}}

====Esters====
* [[Methyl propionate]] {{chem|C|2|H|5|(CO)OCH|3}}
* [[Ethyl propionate]] {{chem|C|2|H|5|(CO)OC|2|H|5}}
* [[Propyl propionate]] {{chem|C|2|H|5|(CO)OC|3|H|7}}
* [[Pentyl propionate]] {{chem|C|2|H|5|(CO)OC|5|H|11}}
* [[Fluticasone propionate]] {{chem|C|25|H|31|F|3|O|5|S}}

==See also==
* [[List of saturated fatty acids]]
* [[List of carboxylic acids]]

==References==
{{reflist}}

==External links==
{{Commons category|Propionic acid}}
* [https://webbook.nist.gov/cgi/inchi/InChI%3D1S/C3H6O2/c1-2-3(4)5/h2H2%2C1H3%2C(H%2C4%2C5) NIST Standard Reference Data for propanic acid]
* [http://www.inchem.org/documents/icsc/icsc/eics0806.htm International Chemical Safety Card 0806]
* [https://www.cdc.gov/niosh/npg/npgd0529.html NIOSH Pocket Guide to Chemical Hazards]
* [https://journals.sagepub.com/doi/pdf/10.1177/019262338801600217 The Propionic Acids. Gastrointestinal Toxicity in Various Species]
* [https://web.archive.org/web/20130619080113/http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_08ac/0901b803808ac9fd.pdf?filepath=oxysolvents%2Fpdfs%2Fnoreg%2F327-00019.pdf&fromPage=GetDoc Propionic Acid Technical Data Sheet]
{{Fatty acids}}
{{Authority control}}

{{DEFAULTSORT:Propionic Acid}}
[[Category:Propionic acids| ]]
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