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stearic acid[′stir·ik ′as·əd]
(also n-octadecanoic acid), CH3(CH2)16COOH, a monobasic saturated aliphatic carboxylic acid. The acid takes the form of colorless crystals and has a melting point of 69.6°C and a boiling point of 376.1°C. It is insoluble in water but soluble in ether. Stearic acid is one of the most common higher fatty acids in nature; glycerides of stearic acid are the main component of many fats and oils, from which stearic acid is isolated by hydrolysis, usually in the form of stearin—a mixture of stearic and palmitic acids. Stearic acid may be obtained by fractional precipitation or distillation from stearin and by the hydrogenation of oleic acid. Alkali salts of stearic acid are soaps. Pure stearic acid is used in organic synthesis and in analytical chemistry, where it serves to identify Ca, Mg, and Li, while technical-grade acid is used as a dispersing agent of the ingredients and a vulcanization activator in the production of rubber. The stearates of sodium, lithium, calcium, lead, and other metals are used as constituents of lubricating greases. Stearic acid and its esters are used in the production of cosmetics.