View source for Propanoic acid

{{chembox
| Watchedfields = changed
| verifiedrevid = 268507772
|   Name = Propanoic acid
|   ImageFileL1 = Propionic_acid_chemical_structure.png
|   ImageSizeL1 = 140px
|   ImageNameL1 = Simplified skeletal formula
|   ImageFileR1 = Propionic_acid_flat_structure.png
|   ImageNameR1 = Full structural formula
|   ImageSizeR1 = 150px
|   ImageFileL2 = Propionic-acid-3D-balls.png
|   ImageSizeL2 = 135px
|   ImageNameL2 = Ball-and-stick model
|   ImageFileR2 = Propionic acid spheres.png
|   ImageNameR2 = Space-filling model
|   ImageSizeR2 = 120px
|   IUPACName = propanoic acid
|   OtherNames = ethanecarboxylic acid, propionic acid
| Section1 = {{Chembox Identifiers
|   SMILES = CCC(=O)O
|   CASNo = 79-09-4
|    CASNo_Ref = {{cascite}}
|   ChemSpiderID = 1005
|   RTECS = UE5950000
  }}
| Section2 = {{Chembox Properties
|   Formula = C<sub>3</sub>H<sub>6</sub>O<sub>2</sub>
|   MolarMass = 74.08 g/mol
|   Appearance = colourless liquid
|   Density = 0.99 g/cm³
|   Solubility = miscible
|   MeltingPtC = −21
|   BoilingPtC = 141
|   pKa = 4.87
|   Viscosity = 10 [[Pascal second|mPa·s]]
  }}
| Section3 = {{Chembox Structure
|   Dipole = 0.63 [[Debye|D]]
  }}
| Section7 = {{Chembox Hazards
|   ExternalMSDS = [[Propionic acid chemdata supplement#Material Safety Data Sheet|External MSDS]]
|   MainHazards = Corrosive
|   NFPA-H = 3
|   NFPA-F = 2
|   NFPA-R =
|   FlashPt = 327 K, 54 °C
|   RPhrases = {{R34}}
|   SPhrases = {{S1/2}} {{S23}} {{S36}} {{S45}}
  }}
| Section8 = {{Chembox Related
|   OtherAnions = [[propionate]]
|   Function = [[carboxylic acid]]s
|   OtherFunctn = [[acetic acid]]<br />[[lactic acid]]<br />[[3-Hydroxypropionic acid|3-hydroxypropionic acid]]<br />[[tartronic acid]]<br />[[acrylic acid]]<br />[[butyric acid]]
|   OtherCpds = [[1-Propanol|1-propanol]]<br />[[propionaldehyde]]<br />[[sodium propionate]]<br />[[propionic anhydride]]}}
}}

'''Propanoic acid''' (also named '''propionic acid''') is a naturally-occurring [[carboxylic acid]] with [[chemical formula]] [[carbon|C]][[hydrogen|H]]<sub>3</sub>CH<sub>2</sub>C[[oxygen|O]]OH.  It is a clear liquid with a pungent odor. The [[anion]] CH<sub>3</sub>CH<sub>2</sub>COO<sup>−</sup> as well as the [[salt (chemistry)|salt]]s and [[ester]]s of propanoic acid are known as [[propanoate]]s (or propionates).

==History==
Propanoic acid was first described in 1844 by [[Johann Gottlieb]], who found it among the degradation products of [[sugar]]. Over the next few years, other chemists produced propanoic acid in various other ways, none of them realizing they were producing the same substance.  In 1847, the French chemist [[Jean-Baptiste Dumas]] established that all the acids were the same compound, which he called propionic acid, from the [[Greek language|Greek]] words ''protos'' = "first" and ''pion'' = "fat", because it was the smallest H(CH<sub>2</sub>)<sub>''n''</sub>COOH acid that exhibited the properties of the other [[fatty acid]]s, such as producing an oily layer when salted out of water and having a [[soap]]y [[potassium]] salt.

==Properties==
Propanoic 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 both as the liquid and vapor.  

Propanoic acid displays the general properties of carboxylic acids: it can form [[amide]], [[ester]], [[acid anhydride|anhydride]], and [[acyl chloride|chloride]] derivatives.  It can undergo alpha-[[halogenation]] with [[bromine]] in the presence of [[phosphorus tribromide|PBr<sub>3</sub>]] as [[catalyst]] (the [[Hell-Volhard-Zelinsky halogenation|HVZ reaction]]) to form CH<sub>3</sub>CHBrCOOH.<ref>{{OrgSynth|author=C. S. Marvel and V. du Vigneaud|title=α-bromo-Isovaleric acid|collvol=2|collvolpages=93|year=1943|prep=cv2p0093}}</ref>

==Production==
In industry, propanoic acid is mainly produced by the hydrocarboxylation of [[ethylene]] using [[nickel carbonyl]] as the catalyst:<ref name=Ullmann>W. Bertleff, M. Roeper, X. Sava, “Carbonylation” in Ullmann’s Encyclopedia of Chemical Technology Wiley-VCH: Weinheim, 2003. DOI: 10.1002/14356007.a05 217.</ref>
:H<sub>2</sub>C=CH<sub>2</sub>  +  H<sub>2</sub>O  +  CO   →   CH<sub>3</sub>CH<sub>2</sub>CO<sub>2</sub>H

It is also produced by the aerobic [[oxidation]] of [[propionaldehyde]].  In the presence of [[cobalt]] or [[manganese]] [[ion]]s, this reaction proceeds rapidly at temperatures as mild as 40–50 °C:
:[[propionaldehyde|CH<sub>3</sub>CH<sub>2</sub>CHO]] + ½ [[oxygen|O<sub>2</sub>]] → CH<sub>3</sub>CH<sub>2</sub>COOH.

Large amounts of propanoic acid were once produced as a byproduct of acetic acid manufacture. Currently the world's largest producer of propanoic acid is [[BASF]], with approximately 80 kt/a production capacity.

Propanoic 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 it is the breakdown of some [[amino acid]]s. [[Bacterium|Bacteria]] of the genus ''[[Propionibacterium]]'' produce propanoic 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 [[Propionibacterium acnes|sweat glands of humans]], and their activity is partially responsible for the odor of both [[Swiss cheese]] and [[sweat]].

==Uses==
Propanoic acid inhibits the growth of [[mold]] and some [[bacterium|bacteria]] at the levels between 0.1 and 1% by weight.  As a result, most propanoic 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. The antibiotic [[Monensin]] is added to cattle feed to favor propionibacteria over acetic acid producers in the rumen; this produces less carbon dioxide and feed conversion is better. This application accounts for about half of the world production of propanoic acid. Another major application is as a preservative in baked goods, which use the [[sodium]] and [[calcium]] salts.<ref name=Ullmann/>

Propanoic acid is also useful as an intermediate in the production of other chemicals, especially polymers. [[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 propanoic acid have fruit-like odors and are sometimes used as [[solvent]]s or artificial flavorings.<ref name=Ullmann/>

==Metabolism==
The metabolism of propanoic acid begins with its conversion to propionyl [[coenzyme A]] (propionyl-CoA), the usual first step in the metabolism of [[carboxylic acid]]s.  Since propanoic acid has three carbons, propionyl-CoA cannot directly enter either [[beta oxidation]] nor the [[citric acid cycle]]s.  In most [[vertebrate]]s, propionyl-CoA is [[carboxylation|carboxylated]] to D-methylmalonyl-CoA, which is [[Isomerisation|isomerised]] to L-methylmalonyl-CoA. A [[vitamin B12]]-dependent enzyme catalyzes rearrangement of L-methylmalonyl-CoA to [[succinyl-CoA]], which is an intermediate of the citric acid cycle and can be readily incorporated there.

In propanoic acidemia, 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 propanoic acidemia when intramitochondrial propionyl-CoA may accumulate. Propanoic acidemia may alter both neuronal and glial gene expression by affecting histone acetylation.<ref name = macfabe>{{cite journal 
 | author = D. F. MacFabe, D. P. Cain, K. Rodriguez-Capote, A. E. Franklin, J. E. Hoffman, F. Boon, A. R. Taylor, M. Kavaliers and K.-P. Ossenkopp
 | journal = Behavioral 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 
 | url = }}</ref><ref>{{cite journal 
 | author = N. H. T. Nguyen, C. Morland, S. Villa Gonzalez, F. Rise, J. Storm-Mathisen, V. Gundersen, B. Hassel
 | journal = Journal of Neurochemistry
 | title = Propionate increases neuronal histone acetylation, but is metabolized oxidatively by gli. Relevance for propionic acidemia
 | year = 2007
 | volume = 101 
 | issue = 3
 | pages = 806–814
 | doi = 10.1111/j.1471-4159.2006.04397.x 
 | url = }}</ref>  Propanoic acid in rodents produces reversible behavior (e.g. [[hyperactivity]], [[dystonia]], social impairment, perseveration) and brain (e.g. innate neuroinflammation, glutathione depletion) changes reminiscent of [[autism]].<ref name = macfabe/> 

===Human occurrence===
The human [[skin]] is host of several species of bacteria known as ''[[Propionibacteria]]'', which are named after their ability to produce propanoic acid.  The most notable one is the ''[[Propionibacterium acnes]]'', which lives mainly in the [[sebaceous gland]]s of the skin and is one of the principal causes of [[acne]].

==References==
{{Reflist}}

==External links==
* [http://webbook.nist.gov/chemistry/ NIST Standard Reference Database]
* [http://ecb.jrc.it/ European Chemicals Bureau]
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc08/icsc0806.htm International Chemical Safety Card 0806]
* [http://www.cdc.gov/niosh/npg/npgd0529.html NIOSH Pocket Guide to Chemical Hazards]
* [http://www.basf.com/static/OpenMarket/Xcelerate/Preview_cid-974236976155_pubid-974236725646_c-Article.html  Technical data of propionic acid of BASF]

{{Fatty acids}}


[[Category:Propionates]]
[[Category:Carboxylic acids]]
[[Category:Analgesics]]

[[cs:Kyselina propionová]]
[[de:Propionsäure]]
[[el:Προπανικό οξύ]]
[[es:Ácido propílico]]
[[fr:Acide propanoïque]]
[[it:Acido propionico]]
[[la:Acidum propionicum]]
[[lv:Propionskābe]]
[[nl:Propionzuur]]
[[ja:プロピオン酸]]
[[pl:Kwas propionowy]]
[[pt:Ácido propanoico]]
[[ru:Пропионовая кислота]]
[[sk:Kyselina propiónová]]
[[fi:Propionihappo]]
[[sv:Propansyra]]
[[vi:Axít prôpionic]]
[[zh:丙酸]]
[[Category:2Fix]]