Propanoic acid is a short-chain saturated carboxylic acid with the molecular formula C3H6O2 and CAS registry number 79-09-4. Its most familiar alternative name is propionic acid, and in concentrated form it is a colourless, oily liquid with a pungent, rancid odour. The compound is fully miscible with water and most organic solvents, which underpins its use as a preservative, a reaction medium, and a chemical intermediate.
What Is Another Name for Propanoic Acid?
The most common alternative name is propionic acid, and the two terms are used interchangeably in industry and in the scientific literature. Propylic acid and ethylformic acid also appear in older documents, while the anion and its salts are collectively called propionates. All of these names describe the same substance: a three-carbon carboxylic acid with the formula C3H6O2 and a molecular weight of about 74.08.
| Name type | Term |
|---|---|
| Preferred IUPAC name | Propanoic acid |
| Common name | Propionic acid |
| Older synonyms | Propylic acid, ethylformic acid |
| Salt nomenclature | Propionates (sodium, calcium, potassium) |
| CAS registry number | 79-09-4 |
Physical and Chemical Properties
| Property | Typical value |
|---|---|
| Molecular formula | C3H6O2 (CH3CH2COOH) |
| Molecular weight | 74.08 |
| Appearance | Colourless, clear oily liquid with a pungent odour |
| Melting point | minus 24 to minus 23 °C |
| Boiling point | 141.7 °C |
| Flash point | 51.7 °C (closed cup) |
| Density | about 0.99 g/cm³ at 20 °C |
| Solubility | Miscible with water, ethanol, chloroform, and ether |
Propanoic acid is a weak acid in dilute aqueous solution, with a pKa of about 4.9, but it is corrosive in concentrated form and its vapours irritate the skin, eyes, and respiratory tract. Vapour can form explosive mixtures with air, so storage areas must be cool and well ventilated and kept clear of ignition sources and strong oxidising agents. For transport it is classified as a corrosive substance and is handled in corrosion-resistant equipment.
Feed and Food Preservation Uses
Propionic acid and its salts are widely used to inhibit mould and bacterial growth in animal feed and in food. The undissociated acid is the active form, which is why the preservative effect is strongest in the mildly acidic pH range typical of silage, grain, and baked goods. In the European food additive system, propionic acid is listed as E280, with E281 for sodium propionate, E282 for calcium propionate, and E283 for potassium propionate.
Animal feed - mould inhibition in grain, compound feed, and silage
Bakery - calcium and sodium propionates delay mould growth and extend shelf life
Dairy and beverage - selected applications where acidulant and preservative effects are both useful
Buyers serving these markets normally require food-grade or feed-grade documentation in addition to the standard certificate of analysis, since purity limits for heavy metals and residual solvents differ from those applied to technical grades.
Industrial Solvent and Intermediate Applications
Technically, propanoic acid acts as a solvent in coatings, dyes, and resins, and as an intermediate for a broad family of derivatives. Its short carbon chain makes it a compact building block for introducing a three-carbon acid function into a larger molecule.
Herbicides - esters and salts used as selective weed-control actives
Cellulose esters - plasticising and property-modifying components
Plasticizers - ester derivatives for flexible polymer systems
Pharmaceuticals - synthesis routes for anti-inflammatory and other active ingredients
Perfume esters - fruity and floral notes built on propionate esters
Rubber chemicals - vulcanisation and processing additives
Each application carries its own grade requirement, so the same CAS number can be bought as a technical grade, a food grade, or a feed grade with different impurity profiles and packaging.
Packaging, Storage and Buyer Checks
Propanoic acid is supplied in drums, intermediate bulk containers, and road tankers, with lined or corrosion-resistant materials throughout because the concentrated acid attacks ordinary carbon steel. Storage tanks should be vented to a safe location, kept away from oxidising agents and bases, and provided with secondary containment. Personnel handling the material need chemical-resistant gloves, face protection, and respiratory protection where ventilation is inadequate.
Before purchase, buyers should confirm the assay and the grade, request a certificate of analysis and an up-to-date safety data sheet, and verify the transport classification and packaging marks. Where the material is destined for feed or food use, the supplier should also provide the appropriate compliance documentation, and incoming inspection should check colour, assay, and water content against the agreed specification.
Frequently Asked Questions
Q: What is another name for propanoic acid?
The most common alternative name is propionic acid. Propylic acid and ethylformic acid are older synonyms for the same compound.
Q: What is the CAS number of propanoic acid?
Propanoic acid has the CAS registry number 79-09-4 and the molecular formula C3H6O2.
Q: Is propanoic acid the same as propionic acid?
Yes. Propanoic acid and propionic acid are two names for the same chemical substance.
Q: What is propanoic acid used for?
It is used as a preservative in feed and food, as an industrial solvent, and as an intermediate for herbicides, esters, plasticizers, and pharmaceuticals.
Q: What is the boiling point of propanoic acid?
The boiling point is approximately 141.7 °C and the closed-cup flash point is about 51.7 °C.
Q: Is propanoic acid corrosive?
Yes. It is a weak acid when dilute but corrosive in concentrated form, and its vapours irritate the skin, eyes, and respiratory tract.