Oleic Acid

OLEIC ACID, Acidum oleinicum, or Acidum elainicum, CH₃(CH₂)₇CH=CH(CH₂)₇COOH, is found as a glyceride, triolein (olein), in varying amounts in most liquid or solid animal and vegetable fats. The highest amounts of oleic acid are contained in almond and olive oils, as well as in whale and seal blubber. The room-temperature-liquid portion of animal fats consists almost exclusively of triolein. So-called "non-drying" vegetable oils consist predominantly of triolein mixed with tripalmitin and tristearin, and with only a small amount of other unsaturated acids, such as linoleic and isolinoleic acids. Drying oils contain very little oleic acid. To obtain oleic acid, almond or olive oil, the liquid portion of animal fats, or technical oleic acid from stearin factories is used. The fats are saponified with potassium or sodium lye. The soap is decomposed with sulfuric acid, and the resulting fatty acids are converted into water-insoluble lead salts; the precipitate of lead salts is collected on a filter, dried, and extracted with ether, whereby lead oleate dissolves in the ether while the salts of other fatty acids remain insoluble. The ethereal extract is shaken with dilute hydrochloric acid; the ethereal layer is separated, the ether is distilled off, yielding almost pure oleic acid; subsequently, by distillation under reduced pressure or by conversion into a barium salt, recrystallization, and decomposition with tartaric acid, oleic acid is obtained in a pure state. Pure oleic acid is colorless, odorless, and tasteless; specific gravity at +15° is 0.890; it solidifies at +4°, melts at +14°, and the boiling point of oleic acid is 285–286° at 100 mm pressure and 223° at 10 mm pressure. Oleic acid itself does not react to litmus paper, but its alcoholic solution reacts acidic. Oleic acid is insoluble in water, readily soluble in alcohol, ether, chloroform, and is also miscible in all proportions with fatty and essential oils. The iodine number of pure oleic acid is ~90, of technical grade 72–82, and the acid number is 199. When stored in air, oleic acid oxidizes and becomes rancid. Crude oleic acid is used for the preparation of plasters, soaps (sodium or potassium oleate), vasoliments, and for the preparation of readily soluble and easily absorbed salts of oleic acid, such as mercury, cocaine, and lead salts. Salts of oleic acid are strong hemolytic poisons. Crude oleic acid is a thick oil, at 15° has a specific gravity of 0.890–0.910, and yields clear solutions with an equal amount of alcohol; it is adopted in the 7th Russian Pharmacopoeia, as well as the Japanese, British, and North American pharmacopoeias.