Oleic acid

Pure oleic acid is a colorless oily liquid with an animal or vegetable oil odor. When exposed to air for a long time, its color gradually darkens. The industrial product is a yellow to red oily liquid with a lard-like odor.

Pure oleic acid has a melting point of 13-14°C, a boiling point of 360°C, a relative density of 0.8935 (20/4°C), a vapor pressure of 52 mm Hg (37°C), a refractive index of 1.4585-1.4605, and a flash point of 270.1°C. It is flammable and incompatible with strong oxidizers and aluminum.

It is easily soluble in organic solvents such as ethanol and chloroform but insoluble in water. It is flammable. It saponifies easily with alkali and forms a white soft solid after solidification. It oxidizes, polymerizes, or decomposes readily at high temperatures. It is non-toxic.

Oleic acid is mainly derived from nature and exists in the form of glycerides in animal and vegetable fats. Oils with high oleic acid content can be saponified, acidified, and separated to obtain oleic acid. Oleic acid has cis and trans isomers; natural oleic acid is in the cis form (the trans form cannot be absorbed by the human body). It has certain effects in softening blood vessels and plays an important role in the metabolism of humans and animals. However, the oleic acid synthesized by the human body is insufficient, so it must be obtained from food. Therefore, consuming oils with high oleic acid content is beneficial to health.

When oleic acid reacts with nitric acid, it isomerizes into the trans isomer, elaidic acid, which has a melting point of 44-45°C. Hydrogenation yields stearic acid. Due to the presence of a double bond, oleic acid undergoes autoxidation when exposed to air for a long time, partially converting into carbonyl-containing substances, which is the cause of oil rancidity. Commercial oleic acid generally contains 7%-12% saturated fatty acids, such as palmitic acid and stearic acid.

The sodium or potassium salt of oleic acid is one of the components of soap. Pure sodium oleate has good detergency and can be used as an emulsifier or other surfactant. It is also used in the treatment of cholelithiasis. Other metal salts of oleic acid are used in waterproof fabrics, lubricants, polishes, etc. Its barium salt can be used as a rodenticide.