Propanoic acid

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Propanoic acid
Simplified skeletal formula Full structural formula
Ball-and-stick model Space-filling model
CAS number 79-09-4 YesY
PubChem 1032
ChemSpider 1005 YesY
DrugBank DB03766
ChEBI CHEBI:30768 YesY
RTECS number UE5950000
Jmol-3D images Image 1
Image 3
Molecular formula C3H6O2
Molar mass 74.08 g mol−1
Appearance Colorless liquid
Odor Slightly rancid
Density 0.98797 g/cm3[1]
Melting point −20.5 °C (−4.9 °F; 252.7 K) [7]
Boiling point 141.15 °C (286.07 °F; 414.30 K) [7]
Sublimes at −48 °C
ΔsublHo = 74 kJ/mol[2]
Solubility in water 8.19 g/g (−28.3 °C)
34.97 g/g (−23.9 °C)
Miscible (≥ −19.3 °C)[3]
Solubility Miscible in EtOH, ether, CHCl3[4]
log P 0.33[5]
Vapor pressure 0.32 kPa (20 °C)[6]
0.47 kPa (25 °C)[5]
9.62 kPa (100 °C)[2]
4.45·10−4 L·atm/mol[5]
Acidity (pKa) 4.88[5]
Thermal conductivity 1.44·105 W/m·K
Viscosity 1.175 cP (15 °C)[1]
1.02 cP (25 °C)
0.668 cP (60 °C)
0.495 cP (90 °C)[5]
Crystal structure Monoclinic (−95 °C)[8]
Space group P21/c[8]
Lattice constant a = 4.04 Å, b = 9.06 Å, c = 11 Å[8]
Lattice constant α = 90°, β = 91.25°, γ = 90°
Dipole moment 0.63 D (22 °C)[1]
152.8 J/mol·K[4][2]
191 J/mol·K[2]
−510.8 kJ/mol[2]
1527.3 kJ/mol[1][2]
MSDS External MSDS
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[6]
GHS signal word Danger
P280, P305+351+338, P310[6]
EU classification Corrosive C
R-phrases R10, R34
S-phrases (S1/2), S23, S36, S45
Main hazards Corrosive
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuel Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 54 °C (129 °F; 327 K) [6]
Autoignition temperature 512 °C (954 °F; 785 K)
LD50 1370 mg/kg (white mice, oral)[4]
Related compounds
Other anions Propanoate
Related Carboxylic acids Acetic acid
Lactic acid
3-hydroxypropionic acid
Tartronic acid
Acrylic acid
Butyric acid
Related compounds 1-Propanol
Sodium propionate
Propionic anhydride
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Propanoic acid (also known as propionic acid from the Greek words protos, meaning first, and pion, meaning fat) is a naturally occurring carboxylic acid with chemical formula CH3CH2COOH. It is a clear liquid with a pungent and unpleasant smell somewhat resembling body odor. The anion CH3CH2COO as well as the salts and esters of propanoic acid are known as propanoates (or propionates).


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 all the acids to be the same compound, which he called propionic acid, from the Greek words protos, meaning first, and pion, meaning fat, because it is the smallest H(CH2)nCOOH acid that exhibits the properties of the other fatty acids, such as producing an oily layer when salted out of water and having a soapy potassium salt.


Propanoic acid has physical properties intermediate between those of the smaller carboxylic acids, formic and acetic acids, and the larger fatty acids. It is miscible with water, but can be removed from water by adding salt. As with acetic and formic acids, it consists of hydrogen bonded pairs of molecules as both the liquid and the vapor.

Propanoic acid displays the general properties of carboxylic acids: It can form amide, ester, anhydride, and chloride derivatives. It can undergo alpha-halogenation with bromine in the presence of PBr3 as catalyst (the HVZ reaction) to form CH3CHBrCOOH.[10]


In industry, propanoic acid is mainly produced by the hydrocarboxylation of ethylene using nickel carbonyl as the catalyst:[11]

H2C=CH2 + H2O + CO → CH3CH2CO2H

It is also produced by the aerobic oxidation of propionaldehyde. In the presence of cobalt or manganese ions, this reaction proceeds rapidly at temperatures as mild as 40–50 °C:


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

Propanoic acid is produced biologically as its coenzyme A ester, propionyl-CoA, from the metabolic breakdown of fatty acids containing odd numbers of carbon atoms, and also from the breakdown of some amino acids. Bacteria of the genus Propionibacterium produce propanoic acid as the end-product of their anaerobic metabolism. This class of bacteria is commonly found in the stomachs of ruminants and the sweat glands of humans, and their activity is partially responsible for the odor of both Swiss cheese and sweat.

It is also biosynthesized in the large intestine of humans by bacterial fermentation of dietary fibre.[12]

Industrial uses[edit]

Propanoic acid inhibits the growth of mold and some 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.[11] As a food additive, it is approved for use in the EU,[13] USA[14] and Australia and New Zealand.[15] It is listed by its INS number (280) or E number E280.

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 pesticides and pharmaceuticals. The esters of propanoic acid have fruit-like odors and are sometimes used as solvents or artificial flavorings.[11]

Biological uses[edit]

The metabolism of propanoic acid begins with its conversion to propionyl coenzyme A (propionyl-CoA), the usual first step in the metabolism of carboxylic acids. Since propanoic acid has three carbons, propionyl-CoA cannot directly enter either beta oxidation or the citric acid cycles. In most vertebrates, propionyl-CoA is carboxylated to D-methylmalonyl-CoA, which is 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, 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 propanoic acidemia when intramitochondrial propionyl-CoA may accumulate. Propanoic acidemia may alter both neuronal and glial gene expression by affecting histone acetylation.[16][17] When propanoic 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.[16]

It also, being a three-carbon molecule, feeds into hepatic gluconeogenesis (that is, the creation of glucose molecules from simpler molecules in the liver).[18]

Human occurrence[edit]

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 glands of the skin and is one of the principal causes of acne.


  1. ^ a b c d e Lagowski, J.J., ed. (2012). The Chemistry of Nonaqueous Solvents III. Elsevier. p. 362. ISBN 0323151035. 
  2. ^ a b c d e f Propanoic acid in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. (retrieved 2014-06-13)
  3. ^ Seidell, Atherton; Linke, William F. (1919). Solubilities of Inorganic and Organic Compounds (2nd ed.). D. Van Nostrand Company. p. 569. 
  4. ^ a b c
  5. ^ a b c d e CID 1032 from PubChem
  6. ^ a b c d e Sigma-Aldrich Co., Propionic acid. Retrieved on 2014-06-13.
  7. ^ a b Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0. 
  8. ^ a b c Strieter, F. J.; Templeton, D. H.; Scheuerman, R. F.; Sass, R. L. (1962). "The crystal structure of propionic acid". Acta Crystallographica 15 (12): 1233. doi:10.1107/S0365110X62003278.  edit
  9. ^ NIOSH Pocket Guide to Chemical Hazards 0529
  10. ^ C. S. Marvel; V. du Vigneaud (1931), "α-bromo-Isovaleric acid", Org. Synth. 11: 20 ; Coll. Vol. 2: 93 
  11. ^ a b c W. Bertleff; M. Roeper; X. Sava (2005), "Carbonylation", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a05_217 
  12. ^ den Besten, G; van Eunen, K; Groen, AK; Venema, K; Reijngoud, DJ; Bakker, BM (September 2013). "The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism.". Journal of Lipid Research 54 (9): 2325–40. doi:10.1194/jlr.R036012. PMID 23821742. 
  13. ^ "Current EU approved additives and their E Numbers". UK Food Standards Agency. Retrieved 2011-10-27. 
  14. ^ "Listing of Food Additives Status Part II". US Food and Drug Administration. Retrieved 2011-10-27. 
  15. ^ "Standard 1.2.4 - Labelling of ingredients". Australia New Zealand Food Standards Code. Retrieved 2011-10-27. 
  16. ^ a b D. F. MacFabe; D. P. Cain; K. Rodriguez-Capote; A. E. Franklin; J. E. Hoffman; F. Boon; A. R. Taylor; M. Kavaliers; K.-P. Ossenkopp (2007). "Neurobiological effects of intraventricular propionic acid in rats: Possible role of short-chain fatty acids on the pathogenesis and characteristics of autism spectrum disorders". Behavioral Brain Research 176 (1): 149–169. doi:10.1016/j.bbr.2006.07.025. 
  17. ^ N. H. T. Nguyen; C. Morland; S. Villa Gonzalez; F. Rise; J. Storm-Mathisen; V. Gundersen; B. Hassel (2007). "Propionate increases neuronal histone acetylation, but is metabolized oxidatively by glia. Relevance for propionic acidemia". Journal of Neurochemistry 101 (3): 806–814. doi:10.1111/j.1471-4159.2006.04397.x. PMID 17286595. 
  18. ^ Aschenbach, JR; Kristensen, NB; Donkin, SS; Hammon, HM; Penner, GB (December 2010). "Gluconeogenesis in dairy cows: the secret of making sweet milk from sour dough.". IUBMB Life 62 (12): 869–77. doi:10.1002/iub.400. PMID 21171012. 

External links[edit]