OLEIC ACID, C13H34O2 or C8H17·CH:CH·[CH2]7·CO2H, an organic acid occurring as a glyceride, triolein, in nearly all fats, and in many oils—olive, almond, cod-liver, &c. (see Oils). It appears as a by-product in the manufacture of candles. To prepare it olive oil is saponified with potash, and lead acetate added; the lead salts are separated, dried, and extracted with ether, which dissolves the lead oleate; the solution is then treated with hydrochloric acid, the lead chloride filtered off, the liquid concentrated, and finally distilled under diminished pressure. Oleic acid is a colourless, odourless solid, melting at 14° and boiling at 223° (10 mm.). On exposure it turns yellow, becoming rancid. Nitric acid oxidizes it to all the fatty acids from acetic to capric. Nitrous acid gives the isomeric elaidic acid, C8H17·CH:CH·[CH2]7·CO2H, which is crystalline and melts at 51°. Hydriodic acid reduces both oleic and elaidic acids to stearic acid.
Erucic acid, C8H17·CH:CH·[CH2]11·COH, and the isomeric brassidic acid, belong to the oleic acid series. They occur as glycerides in rape-seed oil, in the fatty oil of mustard, and in the oil of grape seeds. Linoleic acid, C18H32O2, found as glyceride in drying oils, and ricinoleic acid, C18H33(OH)O2, found as glyceride in castor oil, closely resemble oleic acid.