butyric acid byo͞otĭr´ĭk [key] or butanoic acid byo͞otənō´ĭk [key], CH 3CH 2CH 2CO 2H, viscous, foul-smelling, liquid carboxylic acid; m.p. about −5°C; b.p. 163.5°C. It is miscible with water, ethanol, and ether. It is a low molecular weight fatty acid that is present in butter as an ester of glycerol; the odor of rancid butter is due largely to the presence of free butyric acid. Butyric acid is used in the manufacture of plastics. Isobutyric acid, or 2-methylpropanoic acid, (CH 3) 2CHCO 2H, is a geometric isomer of the butyric acid described above; it has different physical properties but similar chemical properties.
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