Propionic acid ( / p r oʊ p i n k _ / , from the Greek words protos , meaning “first”, and pion , meaning “fat”, also known as propanoic acid ) is a naturally occurring carboxylic acid with the chemical formula CH 3 CH 2 CO 2 H . It is a pungent and unpleasant smelling liquid which resembles body odour . The anion CH 3 CH 2 CO 2 – as well as the propionate to salts and esters of propionic acidor known as propanoates .
Propionic acid was first described in 1844 by Johann Gottlieb, who found it in the degradation products of sugar. Over the next few years, other chemists produced propionic acid in different ways, none of them realizing that they were producing the same substance. In 1847, the French chemist Jean-Baptiste Dumas established all acids as a single 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 properties of other fatty acids, such as the formation of an oily layer when salted with water and being a soapy potassium salt.
|chemical formula||C 3 H 6 O 2|
|molar mass||७४.०७९ g·mol −1|
|appearance||colorless, oily liquid|
|dirt||pungent, rancid, unpleasant|
|Melting point||-20.5 °C (-4.9 °F; 252.7 K) |
|boiling point||141.15 °C (286.07 °F; 414.30 K)|
Subl HO = 74
|Solubility in water||8.19 g/g (-28.3 °C)|
34.97 g/g (-23.9 °C) Incorrect ( Mis
-19.3 °C) 
|solubility||Miscible in EtOH, Ether, CHCl 3|
|log p||0.33 |
|vapor pressure||0.32 kPa (20 °C)|
0.47 kPa (25 °C)
9.62 kPa (100 °C)
|Henry’s law constant ( k H )||4.45 10 −4 L atm/mol |
|Acidity ( pKa )||4.88 |
|magnetic susceptibility (χ)||-43.50 10 −6 cm 3 /mol|
|refractive index ( nd )||१.३८४३ |
|viscosity||1.175 CP (15 °C) |
1.02 CP (25 °C)
0.668 CP (60 °C)
0.495 CP (90 °C) 
|crystal structure||Monoclinic (-95 °C) |
|space group||p 2 1 /c |
|lattice constant||A = 4.04 , B = 9.06 , C = 11 α = 90 °, β = 91.25 °, = 90 °|
|dipole moment||0.63 d (22 °C)|
Propionic acid has physical properties intermediate between those of smaller carboxylic acids, formic and acetic acids, and larger fatty acids. This is miscible with water, but can be removed with water by adding salt. As with acetic and formic acids, it consists of hydrogen bonded pairs of molecules in both liquid and vapor.
Propionic acid exhibits properties common to carboxylic acids: it can form amides, esters, anhydrides, and chloride derivatives. This process undergoes the Hell–Volhard–Zelinsky reaction that involves the halogenation of a carboxylic acid with α-bromine, catalyzed by phosphorus tribromide, in this case as 2-bromopropanoic acid, CH3CHBrCOOH .  This product has been used to prepare a racemic mixture of alanine by ammonolysis.
In industry, propionic acid is mainly produced by the hydrocarboxylation of ethylene using nickel-carbonyl as the catalyst:
It is also produced by aerobic oxidation of propionaldehyde. In the presence of cobalt or manganese salts (manganese propionate is most commonly used), this reaction proceeds rapidly at mild temperatures such as 40–50 °C:
Propionic acid was once produced in large quantities as a byproduct of acetic acid manufacture. At present, BASF is the world’s largest producer of propionic acid, with a production capacity of about 150 kt/a.
The biotechnological production of propionic acid primarily uses Propionibacterium strains.  However, the 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).  One approach to improve productivity and yield during fermentation is through the use of cell stabilization techniques, which promote easier recovery, reuse of cell biomass and increase the stress tolerance of microorganisms. . 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 acidipropionii 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 acids production, which could be adapted for other fermentation bioprocesses.  Other cell stabilization metrics have been tested, such as recycled-glass Poravar and fibrous-bed bioreactors.  
Alternative methods of production have been tested by genetically engineering strains of Escherichia coli to incorporate the essential pathway, the Wood–Workman cycle . 
Propionic acid inhibits the growth of mold and certain bacteria at levels of 0.1 to 1% by weight. As a result, some of the propionic acid produced is used 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 animal feed to favor propionibacteria in excess of acetic acid producers in the rumen; It produces less carbon dioxide and better feed conversion. This application accounts for almost half of the world production of propionic acid. Another major application is as a preservative in baked goods, which use sodium and calcium salts.  As a food additive, it is the European Union,  the USA, Approved for use in Australia and New Zealand. 
Propionic acids 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 insecticides and pharmaceuticals. The ester of propionic acids has a fruit-like odor and is sometimes used as solvents or artificial flavoring.
In biogas plants, propionic acids is a common intermediate product, which is made from fermentation by propionic acid bacteria. Its degradation in anaerobic environments (such as biogas plants) requires the activity of complex microbial communities.
Propionic acid is produced biologically as its coenzyme A ester, propionyl-CoA, from the metabolic breakdown of fatty acids with odd numbers of carbon atoms, and also from the breakdown of certain amino acids. Bacteria of the genus Propionibacterium produce propionic acid as an 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 partly responsible for the smell of emmental cheese, American “Swiss cheese”, and sweat.
The metabolism of propionic acid begins with its conversion to propionyl coenzyme A, a common first step in the metabolism of carboxylic acids. Since propionic acid has three carbons, propionyl-CoA cannot directly enter the beta oxidation or citric acid cycle. In most backbones, propionyl CoA is carboxylated to D -methylmalonyl CoA, which is isomerised to L -methylmalonyl CoA. A vitamin B12 dependent enzyme catalyzed rearrangement of L – methylmalonyl CoA to succinyl CoA, which is an intermediate of the citric acid cycle and can be readily incorporated there.
Propionic acid serves as a substrate for hepatic gluconeogenesis through conversion to succinyl-CoA.  [ 29] Additionally, exogenous propionic acid administration results in greater endogenous glucose production, which may be due to gluconeogenic conversion alone.  Exogenous propionic acid may upregulate endogenous glucose production through increases in norepinephrine and glucagon, suggesting chronic ingestion of propionic acid may have adverse metabolic consequences. 
In propionic acidosis, a rare inherited genetic disorder, propionate acts as a metabolic toxin in liver cells as propionyl CoA and its derivative, methylcitrate, cause two tricarboxylic acid cycle inhibitors to be acquired in the mitochondria. Propanoate is metabolized oxidatively by glia, which suggests astrocytic vulnerability in propionic acidosis when intramitochondrial propionyl CoA can accumulate. Propionic acidemia can alter both neuronal and glial gene expression by affecting histone acetylation.  When propionic acid is injected directly into the brains of rodents, it produces aversive behavior (eg, hyperactivity, dystonia, social impairment, perseverance) and brain changes (eg, congenital neuroinflammation, glutathione deficiency) that can be used to A means to model autism in rats. 
Human skin hosts many species of Propionibacteria . The most notable one is Cutibacterium acnes (formerly known as Propionibacterium acnes ), which primarily resides in the sebaceous glands of the skin and is one of the major causes of acne.  Propionate is considered one of the most common short-chain fatty acids produced in the large intestine of humans by the gut microbiota in response to indigestible carbohydrates (dietary fiber) in the diet.   The role of the gut microbiota and their metabolites, including propionate, in mediating brain function has been reviewed. 
A study in rats suggests that propionate is produced in the gut by bacteria of the Bacteroides genus, and that it offers some protection against salmonella there.  Another study found that the fatty acid propionate may calm blood pressure-raising immune cells, protecting the body from the harmful effects of high blood pressure. 
The bacterial species Coprothermobacter platensis produces propionate when gelatin is fermented. 
Propionate salts and esters
propionate / p r oʊ p i n eɪ t _ / or propanoate , the ion is C 2 H 5 C 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 CH 3 CH 2 CO 2 or simply ETCO 2 .
Propionates should not be confused with propenoates (commonly known as acrylates), anions/salts/chemical compounds of propenoic acid (also known as 2-propenoic acid or acrylic acid).
- Sodium Propionate NaC 2 H 5 CO 2
- Potassium Propionate KC 2 H 5 CO 2
- Calcium Propionate Ca (C 2 H 5 CO 2 ) 2
- Zirconium Propionate Zr (C 2 H 5 CO 2 ) 4
- Methyl Propionate (C 2 H 5 (CO) OCH 3 )
- Ethyl Propionate (C 2 H 5 (CO) OC 2 H 5 )
- Propyl Propionate (C 2 H 5 (CO) OC 3 H 7 )
- Pentyl Propionate ( C2H5 ( CO ) OC5H11 )
- Fluticasone propionate C 25 H 31 F 3 O 5 S
Frequently Asked Question
What is propionic acid used for?
According to published scientific literature, propionic acid is primarily used for animal feed preservation (including hay, silage, and grain) and human foods (mainly in baked goods and cheese).
What is the source of propionic acid?
Propionic or propanoic acid is produced when bacteria ferment sugars such as glucose. Naturally occurring propionic bacteria in the sweat glands and intestines produce propionic acid and carbon dioxide in a fermentation reaction.
What is the difference between propionic acid and propanoic acid?
First, in the case of propanoic acid, the C atom is attached to the −COOH group and H+ has to be removed from it. The hybridization is sp3, in which the s character is 25%. Then in propanoic acid, the C atom is attached to the −COOH group and H+ has to be removed from it.
What does propanoic acid look like?
This is propanoic acid, also known as propionic acid. If you want to see and smell an isolated version of this chemical compound, you won’t like it. It is a clear, colorless and oily liquid. It also has a strong musty odor and produces irritating vapors.
What is the nature of propionic acid?
Propionic acid is a short-chain saturated fatty acid containing ethane attached to a carbon of a carboxy group. It has a role as an antifungal drug. It is a short-chain fatty acid and a saturated fatty acid. It is the conjugate acid of a propionate.
What is the meaning of propanoic acid?
Medical definition of propionic acid
: A liquid strong odorous fatty acid C 3 H 6 O 2 found in milk and distillation of wood, coal and petroleum. – Also called propanoic acid.
How do you use propionic acid?
Propionic acid is used as a preservative and flavoring agent in a variety of packaged foods. This includes cheese, but also baked goods such as tortillas and breads. It also finds use as a preservative in animal foods such as hay, corn, oats, wheat, sorghum and barley.
is it propanoic or propionic acid
Propionic acid (/proʊpiˈɒnɪk/, from the Greek words protos, meaning “first”, and pion, meaning “fat”, also known as propionic acid) is a natural compound with the chemical formula CH 3 CH 2 CO 2 H. It is a commonly found carboxylic acid. A liquid with a pungent and unpleasant odor that is somewhat similar to body odor.