Pure oleic acid is a colorless oily liquid with the smell of animal or vegetable oil. When exposed to air for a long time, its color gradually darkens. Industrial oleic acid ranges from yellow to red oily liquid and has a smell of lard. The melting point of pure oleic acid is 13-14°C, and its boiling point is 360°C. Relative density is 0.8935 (20/4°C), vapor pressure: 52mmHg (37°C), refractive index 1.4585-1.4605, flash point 270.1°C. It is flammable and incompatible with strong oxidizers and aluminum. It is easily soluble in organic solvents like ethanol, ether, chloroform, etc., but insoluble in water. Upon contact with alkali, it easily saponifies, forming a white soft solid upon solidification. It is highly susceptible to oxidation, polymerization, or decomposition at high temperatures and is non-toxic.
Oleic acid is mainly derived from nature and exists in animal and vegetable fats in the form of glycerides. Oleic acid can be obtained by saponifying and acidifying fats with high oleic acid content. Oleic acid has cis-trans isomers, with natural oleic acid being in cis form (trans form is not absorbable by the human body). It has certain effects on 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 not sufficient, requiring intake from food, so consuming oils with high oleic acid content is beneficial for health.
When oleic acid reacts with nitric acid, it isomerizes to trans isomer. The melting point of trans-oleic acid is 44-45°C. Hydrogenation converts it to stearic acid. Oxidation with potassium permanganate yields a mixture of nonanoic acid and azelaic acid. Due to the presence of a double bond, oleic acid can undergo auto-oxidation when exposed to air for long periods, partially converting into carbonyl-containing substances with a rancid odor. This is the reason for the spoilage of fats. commercial oleic acid generally contains 7%–12% of saturated fatty acids such as palmitic acid and stearic acid.
Sodium or potassium salts of oleic acid are constituents of soap. Pure oleic acid sodium has good detergent properties and can be used as an emulsifier and other surfactants. It can also be used in treating cholelithiasis. Other metal salts of oleic acid can be used in waterproof fabrics, lubricants, polishes, etc., while its barium salt can be used as a rodenticide.
Oleic acid is an essential nutrient in animal food. Its lead, manganese, and cobalt salts are driers for paint; copper salt is an anti-rotting agent for fishing nets; aluminum salt can be used as a waterproofing agent for fabrics and as a thickener for certain lubricants. Epoxidation of oleic acid can produce epoxy oleate (plasticizer). Oxidative cleavage can produce azelaic acid (a raw material for polyamide resin).
In the wool textile industry, it is used to prepare antistatic agents and lubricating softeners. In the wood industry, it is used to prepare water-resistant paraffin emulsions. Oxidation can produce azelaic acid, which can also be used as an agricultural pesticide emulsifier, lubricant, dyeing assistant, industrial solvent, metal mineral flotation agent, mold release agent, and fat hydrolysis agent. It is used to prepare carbon paper, typing paper, ball pen oil, and various oleates. As a chemical reagent, it is used as a chromatographic comparison sample and in biochemical research to determine calcium, ammonia, and copper, and to measure magnesium and sulfur. It activates protein kinase in liver cells. The 75% ethanol solution of oleic acid can be used as a rust remover.
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