CH3CH2COOH, a monocarboxylic acid of the aliphatic series. It is a colorless liquid with a pungent odor and has a melting point of — 20.8°C, a boiling point of 140.8°C, and a density of 0.993 g/cm3 (20°C). It is soluble in water, alcohol, and ether.
Propionic acid is formed during the fermentation of carbohydrates by propionic acid bacteria and certain other bacteria. In industry it is obtained chiefly through the oxidation of paraffin hydrocarbons as a by-product in the preparation of acetic acid. Propionic acid and its salts (Na, K, and others) are used as fungicides. Propionic anhydride is used in the manufacture of cellulose esters, and geranyl propionate and various other esters are used in perfume bases.