Fatty acids are an essential component of lipids in plants, animals and microbes. We can find oleic acid in all oils and fats to some extent. Oleic acid is an odourless and colourless oil, although some commercial samples may be yellowish. In olive oil, palm oil, peanut oil and sunflower oil, oleic acid is the principal acid obtained by saponification. Like all other fatty acids, oleic acid does not occur in the free state, but we can typically find it as an ester of glycerol, that is, as a glyceride.
Properties of Oleic Acid
Oleic acid has specific salient properties, and we presented below is a list of the same.
Oleic acid is solid with a low melting point.
There are two crystalline forms of oleic acid – a-form and b-form. The former has a melting point of 13.4 degrees C, whereas the latter has a melting point of 16.3 degrees C.
The name ‘oleic acid’ is derived from the Latin word – oleum – which means oil.
It is the most commonly found fatty acid in nature.
The salts and esters of oleic acids are called oleate oil.
The Occurrence of Oleic Acids
Fatty acids or their salts do not occur in their raw form in biological systems. Instead, fatty acids like oleic acids occur as esters that are the greasy materials in many natural oils. We can find oleic acid in fats, the phospholipids that make membranes, cholesterol esters, and wax esters. It is also the most abundantly found fatty acid in the human adipose tissue and the second most abundant acid in human tissues worldwide after palmitic acid.
Oleic acid makes up 59-76 per cent of pecan oil, 36-67 per cent of peanut oil, 60 per cent of macadamia oil and 20-80 per cent of sunflower oil. It is also abundantly present in animal fat, comprising 37-56 per cent of chicken and turkey fat.
Oleic Acid - Chemistry, Synthesis and Behaviour
Oleic acid is a long-chain carboxylic acid. In chemical terms, oleic acid is regarded as a monounsaturated omega-9 fatty acid, abbreviated with a lipid number of 18:1. The biological preparation of oleic acid involves the action of the stearoyl-CoA 9-desaturase enzyme acting on stearoyl-CoA. In effect, dehydrogenation of stearic acid produces the monounsaturated derivative, that is, oleic acid. Oleic acid experiences the reactions of carboxylic acids and alkenes. It is solvable in an aqueous base to produce soaps called oleates. There is an addition of iodine across the double bond. The hydrogenations of double bonds yield the saturated derivative, that is, stearic acid. The occurrence of oxidation at the double bond happens slowly in the air, and we call it rancidification in foodstuffs. Reduction of the carboxylic acid group produces oleyl alcohol. Ozonolysis of oleic acid is an essential route to azelaic acid. The co-product is nonanoic acid.
Structure of Oleic Acid
Oleic acid is an octadec-9-enoic acid wherein the double bond at C-9 has Z (cis) stereochemistry. Its molecule contains one double bond between C9 and C10 with the cis configuration. We can understand the structure of oleic acid from specific reactions. Oleic acid’s treatment with selenium or oxides of nitrogen partially transforms it into the trans-isomer elaidic acid. Its catalytic hydrogenation demonstrates the arrangement of its 18 carbon atoms and the position of the double bond to stearic acid, CH3 (CH2)16CO2H, and its oxidative cleavage to nonanoic acid and azelaic acid. When we treat oleic acid with alkali, the double bond migration occurs, giving a b-unsaturated acid –
CH3(CH2)14CH=CHCO2H – and on further heating with alkali, it gives palmitic acid - CH3(CH2)14CO2H.
Oleic acid displays a carboxylic acid's typical reactions with substituted ethylene, including the formation of a dibromide with bromine and glycol with dilute aqueous potassium permanganate.
Oleic Acid Formula
The formula of oleic acid is - CH3 (CH2)7CH=CH (CH2)7COOH
The oleic acid molecule contains 54 atoms. There are 34 hydrogen atoms, 18 carbon atoms and two oxygen atoms.
Uses of Oleic Acid
There are innumerable uses of oleic acid. We have mentioned some of its critical benefits below.
The usage of oleic acid is prevalent as a component in many foods in the form of triglycerides. It is a part of the regular human diet, being present in animal fats and vegetable oils. Oleic acid is a significant component of soap as an emulsifying agent. It is also used as an emollient.
Pharmaceuticals use small quantities of oleic acid as an excipient.
We can also use oleic acid as an emulsifying or dissolving agent in aerosol products.
Firms also use oleic acid as a soldering flux in stained glass work for attaching a lead.
The use of oleic acid is widespread in the solution phase synthesis of nanoparticles, functioning as a kinetic knob to control nanoparticles' size and morphology.
The concept of oleic acid has paramount importance in chemistry. Our bodies comprise oleic acid in substantial quantities. Moreover, it is also a part of our diet. Thus, learning about oleic acid has an immense academic and practical necessity.