Propionic acid (CAS 79-09-4) is a saturated monocarboxylic acid with the molecular formula CH3CH2COOH and a molecular weight of 74.08 g/mol. It is a colorless, oily liquid with a sharp, pungent, slightly rancid odor. Naturally present in some foods as a fermentation product, propionic acid and its salts are valued across the food, agricultural, pharmaceutical, and fragrance industries for their antimicrobial activity and versatile reactivity.
Properties of Propionic Acid
| Property | Specification |
|---|---|
| Chemical Formula | CH3CH2COOH |
| Molecular Weight | 74.08 g/mol |
| CAS Number | 79-09-4 |
| EINECS Number | 201-176-3 |
| Melting Point | -21.5°C |
| Boiling Point | 141.1°C |
| Solubility | Miscible with water |
| Density | 0.99 g/cm3 |
| Appearance | Colorless oily liquid with pungent odor |
| Flash Point | 54°C (closed cup) |
Because propionic acid is fully miscible with water and most organic solvents, it is easy to dose in liquid formulations, which is one reason for its widespread use in preservation and synthesis.
Food and Feed Preservation
Propionic acid exhibits strong antifungal and mold-inhibiting activity, especially at pH values below 6.0, where it outperforms benzoic acid on a weight basis and is more cost-effective than sorbic acid in many applications. In the food industry it is used to preserve baked goods, cheese products, and other perishable foods, typically in the form of calcium or sodium propionate, which are approved food additives in many jurisdictions. In animal feed, propionic acid and its salts are applied as mold inhibitors to protect grains and compounded feed during storage, reducing spoilage losses and mycotoxin risk.
Agricultural Chemicals and Herbicide Intermediates
In the agrochemical sector, propionic acid is converted into propionamide and other derivatives that serve as intermediates in the manufacture of several herbicides and plant protection products. The short-chain carboxylic acid structure provides a convenient handle for building more complex active molecules, and demand for propionic acid in this segment tracks the global development of selective herbicides for cereal and broadleaf weed control.
Fragrances, Flavors, and Pharmaceutical Uses
The fragrance and flavor industry uses propionic acid to produce esters such as ethyl propionate, isopentyl propionate, linalyl propionate, geranyl propionate, and benzyl propionate. These esters contribute fruity and floral notes used in foods, beverages, cosmetics, and soap perfumes. In the pharmaceutical field, propionic acid is a building block for several active ingredients, and its derivatives appear in analgesic and anti-inflammatory drug families. It is also used as a solvent and plasticizer for cellulose nitrate and in the preparation of nickel-plating solutions and food flavorings.
Storage, Handling, and Safety Considerations
Propionic acid is a flammable liquid with a flash point of 54°C and is corrosive to skin, eyes, and mucous membranes. Store it in tightly sealed containers made of compatible materials such as stainless steel or suitable plastics, in a cool, well-ventilated area away from ignition sources and incompatible materials such as strong oxidizers and bases. When handling the acid, wear chemical-resistant gloves, safety goggles, and protective clothing, and ensure local exhaust ventilation to control vapors. In case of skin contact, rinse immediately with plenty of water and seek medical attention if irritation persists.
Frequently Asked Questions
Is propionic acid the same as vinegar?
No. Vinegar contains acetic acid (CAS 64-19-7). Propionic acid is a different three-carbon carboxylic acid with a stronger, more pungent odor and different preservative characteristics, although both are used in food preservation.
Why is propionic acid a good food preservative?
Undissociated propionic acid molecules penetrate mold and bacterial cell membranes and disrupt internal pH balance, inhibiting growth. The effect is strongest at pH below 6.0, which is why it is effective in baked goods and cheese with moderate acidity.
Is propionic acid safe in food?
Calcium and sodium propionate are approved food preservatives in many countries within specified usage limits. As with all food additives, manufacturers must comply with local food regulations and label requirements.
Can propionic acid be used as a solvent?
Yes. It serves as a solvent for cellulose nitrate and as a plasticizer component, and it is used in nickel-plating solutions and as a chemical reagent in organic synthesis.
What are the main derivatives of propionic acid?
Key derivatives include propionamide (herbicide intermediate), ethyl propionate and other propionate esters (fragrances and flavors), calcium and sodium propionate (food preservatives), and various pharmaceutical intermediates.
How should propionic acid be stored?
Store in sealed, compatible containers in a cool, ventilated area away from heat, ignition sources, oxidizers, and alkalis. Keep containers upright and inspect periodically for leakage, and handle with appropriate personal protective equipment.
