What Is Propanoic Acid?
Propanoic acid, also known as propionic acid, is a short-chain saturated carboxylic acid with CAS number 79-09-4 and molecular formula C3H6O2. It is a colourless, corrosive liquid with a pungent odour and it dissolves readily in water and in most common organic solvents. Because it converts easily into a wide range of secondary compounds, it is a versatile building block for the food, feed, pharmaceutical and chemical industries.
Key Properties
| Property | Value |
|---|---|
| CAS number | 79-09-4 |
| Molecular formula | C3H6O2 |
| Molecular weight | 74.08 g/mol |
| Boiling point | 141 °C |
| Melting point | -21 °C |
| Appearance | Colourless corrosive liquid with pungent odour |
| Solubility | Miscible with water and most common organic solvents |
Food and Feed Preservative Applications
Propanoic acid and its salts - calcium, sodium and potassium propionate - are well-established preservatives. They inhibit the growth of moulds and several bacteria, which extends the shelf life of bread, cakes and other bakery goods as well as cheese, processed meats, fruit and vegetable products and canned foods. International food safety bodies, including the Joint FAO/WHO Expert Committee on Food Additives, have evaluated propionic acid and its salts as acceptable food additives. Permitted maximum levels depend on the food category and the jurisdiction; in bread and bakery products they commonly reach 2,000 to 3,000 mg/kg. Formulators must always check the exact limits that apply in the target market.
In agriculture, propionic acid is used as a feed preservative. Propionate solutions are applied to high-moisture grains stored in silos, such as oats, corn and sorghum, to prevent spoilage by moulds and fungi. The same treatment protects forages such as hay and silage, both on the storage surface and inside the stored mass. By controlling microbial growth, propanoic acid helps preserve the nutritional quality of animal feed through long storage periods.
Pharmaceutical and Chemical Applications
In the pharmaceutical industry propanoic acid is used to synthesise active pharmaceutical ingredients, including antifungal and anti-inflammatory drugs. The propionate group is a common structural motif in drug molecules, and propanoic acid derivatives appear in the manufacture of several medicines and healthcare products.
Propanoic acid also reacts with alcohols such as ethanol and butanol to form propionate esters. These esters serve as solvents in paints, coatings, printing inks and fragrance formulations, and as intermediates for other fine chemicals including plasticizers and flavour compounds, which broadens the industrial reach of the acid considerably.
Regulatory and Compliance Considerations
Food-grade propanoic acid must meet the purity and specification requirements of the relevant food additive standards, and industrial-grade material must never be used in food contact applications. In the European Union, propionic acid and its salts are authorised as food additives E280, E281, E282 and E283, with defined use levels for specific food categories. Maximum permitted concentrations and permitted food categories differ between markets, so users must confirm the applicable regulation for each destination. Shipments should be accompanied by a certificate of analysis, and grade documentation should clearly separate food, feed and technical qualities.
Safety, Handling and Storage
Propanoic acid is corrosive and can cause severe burns to skin and eyes as well as irritation of the respiratory tract if vapours are inhaled. Handle the liquid with chemical-resistant gloves, safety goggles and protective clothing, and work only in a well-ventilated area or under local extraction. In case of skin contact, wash immediately with plenty of water and seek medical attention. Store the material in sealed, corrosion-resistant containers in a cool, dry, ventilated place away from oxidising agents and ignition sources, and follow local regulations for transport and disposal.
Frequently Asked Questions
Q: What is propanoic acid used for?
It is mainly used as a food preservative and a feed preservative, and as a chemical intermediate for pharmaceuticals, propionate ester solvents, plasticizers and flavour compounds.
Q: What is the CAS number of propanoic acid?
The CAS number of propanoic acid is 79-09-4, and its molecular formula is C3H6O2 with a molecular weight of 74.08 g/mol.
Q: Is propionic acid safe in food?
Propionic acid and its salts are authorised food preservatives in many jurisdictions at regulated levels. In bread and bakery products, permitted maximum concentrations commonly reach 2,000 to 3,000 mg/kg depending on the food category and the jurisdiction.
Q: How does propionic acid preserve animal feed?
It is applied to high-moisture grains such as oats, corn and sorghum and to hay and silage, where it inhibits moulds and fungi and protects feed quality during storage.
Q: What are propionate esters?
Propionate esters form when propanoic acid reacts with alcohols. They are used as solvents in paints, coatings, printing inks and fragrances, and as intermediates for other fine chemicals.
Q: Is propanoic acid hazardous?
Yes. It is corrosive and can cause burns to skin and eyes, so appropriate protective equipment, ventilation and safe handling procedures are required at all times.