Propionic acid is a colorless liquid that has a pungent odor and is commonly used in the production of food preservatives, pharmaceuticals, and synthetic fibers. It is also known by several other names including propanoic acid, carboxyethane, and ethylformic acid. Propanoic acid is the IUPAC name for this compound, while carboxyethane describes its chemical structure as a carboxylic acid with an ethane backbone. Ethylformic acid, on the other hand, references its molecular formula, which contains an ethyl group (-CH2CH3) and a formyl group (-CHO). Other synonyms for propionic acid include methylacetic acid, methylformic acid, and n-propylformic acid.