Oleic acid

Oleic acid (DAC86), a monounsaturated fatty acid with the molecular formula:C18H34O2. In its pure state, oleic acid is a colorless, oily liquid which is hardly soluble in water, but readily soluble in ethanol and ether, and which oxidizes slightly in air, turning into a yellowish-brownish liquid and smelling rancid. Oleic acid dissolves well in fatty and essential oils. During fat hardening, oleic acid is converted to stearic acid.

Like many fatty acids, oleic acid (and its salts) is amphiphilic, with a polar, hydrophilic part (the carboxyl group) and a non-polar, lipophilic part (the hydrocarbon chain).

Oleic acid is the most important unsaturated, essential fatty acid in the diet. It occurs in esterified form (usually as glycerol ester) in almost all natural (vegetable and animal) oils and fats, such as: olive oil (70-75%), peanut oil (50-70%), rapeseed oil (50-65%), avocado oil (44-76%), goose fat (41-72%), palm oil (37-42%), lard (36-52%), sesame oil (35-46%), beef tallow (26-45%), sunflower oil (14-65%), grape seed oil (15-20%). With the elaidic acid there is a cis-trans isomerism.

Cosmetics/pharmacy: In cosmetic products oleic acid serves as acid component of emulsifiers

Esters/salts of oleic acid are called oleates. In the trade, oleic acid is usually sold as a mixture with other fatty acids. In most cases a suitable antioxidant is added.

1. Ammon HPT et al (2014) Hunnius Pharmaceutical Dictionary. De Gruyter Publishing House p.1292