Propionic acid, also known as primary oleic acid, is a saturated monocarboxylic acid containing three carbon atoms and one of the typical volatile low-level fatty acids. Chemical formula: CH3CH2COOH. Molecular weight: 74.08. Colorless, clear, oily liquid with an unpleasant rancid odor. Melting point: -20.8°C, boiling point: 140Chemicalbook.99, 41.65 (1330Pa), relative density: 0.9930, refractive index: 1.3869. Ka = 1.34 × 10-5. Miscible with water. Soluble in alcohol, chloroform and ether. Active in chemical properties, acidic, capable of undergoing reactions such as salt formation, esterification and reduction.