Propanoic Acid: Formula, Properties, Risks And Uses

The propionic acid is a saturated fatty acid short chain comprising ethane bonded to the carbon of a carboxy group. Its formula is CH 3 -CH 2 -COOH.The CH3CH2COO- anion as well as the salts and esters of propanoic acid are known as propionates (or propanoates).

It can be obtained from wood pulp residues by fermentation process using bacteria of the genus propionibacterium . It is also made from ethanol and carbon monoxide using a boron trifluoride catalyst (O’Neil, 2001).

Another way to obtain propanoic acid is by the oxidation of propionaldehyde in the presence of cobalt or manganese ions. This reaction develops rapidly at temperatures as low as 40-50 ° C:

2CH 3 CH 2 CHO + O 2 → 2CH 3 CH 2 COOH

The compound is naturally present at low levels in dairy products and is generally produced, along with other short-chain fatty acids, in the gastrointestinal tract of humans and other mammals as the end product of microbial digestion of carbohydrates.

It has a significant physiological activity in animals (Human Metabolome Database, 2017).

Physical and chemical properties

Propanoic Acid is a colorless, oily liquid with a pungent, unpleasant, rancid odor. Its appearance is shown in figure 2 (National Center for Biotechnology Information, 2017).

propionic acid in physical appearance

Propanoic acid has a molecular weight of 74.08 g / mol and a density of 0.992 g / ml. Its freezing and boiling points are -20.5 ° C and 141.1 ° C respectively. Propanoic acid is a weak acid whose pKa is 4.88.

The compound is very soluble in water, being able to dissolve 34.97 grams of compound for every 100 ml of solvent. It is also soluble in ethanol, ether, and chloroform (Royal Society of Chemistry, 2015).

Propanoic acid has physical properties intermediate between those of the smaller carboxylic acids, formic and acetic acids, and the larger fatty acids.

It shows the general properties of carboxylic acids and can form amide, ester, anhydride, and chloride derivatives. It can undergo alpha-halogenation with bromine in the presence of PBr3 as a catalyst (the HVZ reaction) to form CH3CHBrCOOH.

Reactivity and hazards

Propanoic acid is a flammable and combustible material. It can be ignited by heat, sparks, or flames. Vapors can form explosive mixtures with air, being able to travel to source of ignition and explode.

Most vapors are heavier than air. They will be spread along the ground and collected in low or confined areas (sewers, basements, tanks). Vapor explosion hazard indoors, outdoors, or in sewers.

Substances designated with a (P) can polymerize explosively when heated or enveloped in a fire. Containers can explode when heated (PROPIONIC ACID, 2016).

The compound should be kept away from heat or sources of ignition. When heated to decomposition it emits acrid smoke and irritating fumes.

Propanoic acid is irritating to the skin, eyes, nose and throat but does not produce acute systemic effects and has no demonstrable genotoxic potential. In case of contact, it should be washed with plenty of water (Material Safety Data Sheet Propionic acid, 2013).


The conjugated base of propanoic acid, propionate, is formed as the terminal three-carbon fragment (activated with coenzyme A as propionyl-CoA) in the oxidation of the odd-numbered carbon fatty acids and the oxidation of the side chain of cholesterol.

Experiments with radioactive isotopes of propionate injected into fasting rats indicate that it may appear in glycogen, glucose, intermediates of the citric acid cycle, amino acids, and proteins.

The propanoic acid pathway of metabolism involves interaction with coenzyme A, carboxylation to form methylmalonyl-coenzyme A, and conversion to succinic acid, which enters the citric acid cycle.

Propanoic acid can be oxidized without forming ketone bodies and, in contrast to acetic acid, it is incorporated into a carbohydrate as well as a lipid (Bingham, Cohrssen, & Powell, 2001).

Propionic aciduria is one of the most common organic aciduria, a disease that encompasses many diverse disorders.

The outcome of patients born with propionic aciduria is poor in intellectual development patterns, with 60% having an IQ less than 75 and requiring special education.

Successful liver and / or kidney transplants in a few patients have resulted in a better quality of life but have not necessarily prevented viscera and neurological complications.

These results emphasize the need for permanent metabolic monitoring, regardless of the therapeutic strategy.


Propanoic acid inhibits bacterial and mold growth at levels between 0.1 and 1% by weight. As a result, most of the propanoic acid produced is consumed as a preservative for both animal feed and food for human consumption such as grains and cereals.

The preservation of feed, cereals and food in addition to the production of calcium and sodium propionates which represents almost 80% of the global consumption of propanoic acid in 2016, compared to 78.5% in 2012.

Approximately 51% of the global consumption of propanoic acid goes to animal feed and grain preservation, while almost 29% is used in the production of calcium and sodium propionates, which are also used in the food and feed industry .

Other important markets for propanoic acid are herbicide and diethyl ketone production. Lower volume applications include making cellulose acetate propionate, pharmaceuticals, solvent esters, flavorings and fragrances, plasticizers, dyes, and textile, leather, and rubber auxiliaries.

The demand for propanoic acid is highly dependent on feed and grain production, followed by packaged foods and bakery products.

The global growth prospects for propanoic acid and its salts in animal feed / grain preservation and food are significant (IHS Markit, 2016).

Other fast growing markets include propionate esters for solvents, such as n-butyl and pentyl propionate; These esters are increasingly used as substitutes for solvents listed as dangerous air pollutants.


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  4. IHS Markit. (2016, December). Chemical Economics Handbook Propionic Acid. Recovered from ihs:
  5. Material Safety Data Sheet Propionic acid. (2013, May 21). Recovered from sciencelab:
  6. National Center for Biotechnology Information. . (2017, April 22). PubChem Compound Database; CID = 1032. Recovered from
  7. O’Neil, M. (. (2001). The Merck Index – An Encyclopedia of Chemicals, Drugs, and Biologicals. 13th Edition. New Jersey: Merck and Co., Inc.
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  9. Royal Society of Chemistry. (2015). Propionic acid. Recovered from chemspider:

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