BUTYRIC ACID

also called butanoic acid (CH3CH2CH2CO2H) a fatty acid occurring in the form of esters in animal fats and plant oils. As a glyceride, it makes up 34 percent of butter; the disagreeable odour of rancid butter is that of butyric acid resulting from hydrolysis of the glyceride. The acid is of considerable commercial importance as a raw material in the manufacture of esters of lower alcohols for use as flavouring agents; its anhydride is used to make cellulose acetatebutyrate, a useful plastic. Butyric acid is manufactured by aerial oxidation of butyraldehyde. It is a colourless liquid, soluble in water and miscible with common organic solvents; it freezes at -4.26 C (24.33 F) and boils at 163.53 C (326.35 F). An isomer, isobutyric acid (CH3)2CHCO2H, or 2-methylpropanoic acid, is found both in the free state and as its ethyl ester in a few plant oils. It is commercially less important than butyric acid. It is generally similar to butyric acid; it freezes at -46.1 C (-51 F) and boils at 153.2 C (307.8 F).