Propanoic acid

Propanoic acid
IUPAC name propanoic acid
Other names ethanecarboxylic acid, propionic acid
Identifiers
CAS number	79-09-4 Y
PubChem	1032
ChemSpider	1005 Y
DrugBank	DB03766
ChEBI	CHEBI:30768 Y
ChEMBL	CHEMBL14021 Y
RTECS number	UE5950000
Jmol-3D images	Image 1
SMILES CCC(=O)O
InChI InChI=1S/C3H6O2/c1-2-3(4)5/h2H2,1H3,(H,4,5) Y Key: XBDQKXXYIPTUBI-UHFFFAOYSA-N Y
Properties
Molecular formula	C3H6O2
Molar mass	74.08 g mol−1
Appearance	colourless liquid
Odor	slightly rancid
Density	0.99 g/cm³
Melting point	−21 °C; −6 °F; 252 K
Boiling point	141 °C; 286 °F; 414 K
Solubility in water	miscible
Acidity (pKa)	4.87
Viscosity	10 mPa·s
Structure
Dipole moment	0.63 D
Hazards
MSDS	External MSDS
R-phrases	R34
S-phrases	(S1/2) S23 S36 S45
Main hazards	Corrosive
NFPA 704	2 3 0
Flash point	54 °C; 129 °F; 327 K
Autoignition temperature	512 °C; 954 °F; 785 K
Related compounds
Other anions	Propionate
Related carboxylic acids	Acetic acid Lactic acid 3-hydroxypropionic acid Tartronic acid Acrylic acid Butyric acid
Related compounds	1-propanol Propionaldehyde Sodium propionate Propionic anhydride
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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 odor. The anion CH₃CH₂COO⁻ as well as the salts and esters of propanoic acid are known as propanoates (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 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.

Properties

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.^[1]

Production

In industry, propanoic acid is mainly produced by the hydrocarboxylation of ethylene using nickel carbonyl as the catalyst:^[2]

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:

CH₃CH₂CHO + ½ O₂ → CH₃CH₂COOH.

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 80 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.

Uses

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.^[2] As a food additive, it is approved for use in the EU,^[3] USA^[4] and Australia and New Zealand.^[5] 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.^[2]

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 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.^[6][7] When propanoic acid is infused directly into rodents brains it produces reversible behavior (e.g., hyperactivity, dystonia, social impairment, perseveration) and brain (e.g., innate neuroinflammation, glutathione depletion) changes that may be used as a means to model autism in rats.^[6]

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

References

External links

• NIST Standard Reference Database
• International Chemical Safety Card 0806
• NIOSH Pocket Guide to Chemical Hazards
• Technical data of propionic acid of BASF
• Neurobiological effects of intraventricular propionic acid in ratsPossible role of short chain fatty acids on the pathogenesis and characteristics of autism spectrum disorders
• The Propionic Acids. Gastrointestinal Toxicity in Various Species
• Propionic Acid Technical Data Sheet