Key Physical and Chemical Properties of Oleic Acid
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.
Conclusion
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.
FAQs on Oleic Acid: Structure, Properties & Applications
1. What is oleic acid and what is its chemical formula?
Oleic acid is a naturally occurring fatty acid found in various animal and vegetable fats and oils. Chemically, it is classified as a monounsaturated omega-9 fatty acid, meaning it has a single double bond in its hydrocarbon chain. Its chemical formula is C₁₈H₃₄O₂. It is one of the most common and widely distributed fatty acids in nature.
2. What are the key physical and chemical properties of oleic acid?
Oleic acid exhibits distinct properties that are important for its applications.
- Physical Properties: It is a pale yellow or brownish-yellow oily liquid with a lard-like odour. It is insoluble in water but soluble in organic solvents like alcohol, ether, and chloroform. Its melting point is 13.4 °C.
- Chemical Properties: As a carboxylic acid, it can form esters. Due to the double bond, it undergoes addition reactions such as hydrogenation (which converts it to stearic acid) and halogenation.
3. What are the main commercial and industrial applications of oleic acid?
Oleic acid is a versatile compound used across several industries. Its primary applications include:
- Food Industry: It is a major component of many cooking oils, most notably olive oil, and is used in the preparation of synthetic butters and cheeses.
- Soaps and Detergents: It is used in the manufacturing of soaps (saponification) and other cleaning agents.
- Cosmetics: It acts as an emollient (softening agent) in various skincare products, lotions, and creams.
- Pharmaceuticals: It is used as an excipient in drug formulations to improve the solubility and bioavailability of active ingredients.
4. Where is oleic acid naturally found in high concentrations?
Oleic acid is abundant in nature, particularly in vegetable oils. The most significant sources include:
- Olive oil, which can contain 55% to 83% oleic acid.
- Canola oil
- Peanut oil
- Sunflower oil (high-oleic varieties)
- Sesame oil
5. How is the structure of oleic acid related to its properties as an omega-9 fatty acid?
The structure of oleic acid is key to its function. It has an 18-carbon chain with a carboxylic acid group (-COOH) at one end. The term 'omega-9' signifies that its single double bond is located at the ninth carbon atom counting from the methyl end (the 'omega' end) of the chain. This single double bond creates a 'kink' or bend in the molecule, preventing the chains from packing tightly together. This is why oleic acid is a liquid at room temperature, unlike its saturated counterpart, stearic acid.
6. Why is oleic acid classified as a monounsaturated fat, and what is the significance of its 'cis' configuration?
Oleic acid is classified as 'monounsaturated' because its hydrocarbon tail contains exactly one carbon-carbon double bond (C=C). In contrast, saturated fats have no double bonds, and polyunsaturated fats have two or more. The natural configuration of this double bond is 'cis', which means the hydrogen atoms attached to the double-bonded carbons are on the same side. This cis-isomerism causes a significant bend in the molecular structure, which is crucial for the fluidity of cell membranes and explains its low melting point.
7. How does oleic acid differ from linoleic acid and stearic acid in terms of structure and saturation?
These three fatty acids all have an 18-carbon backbone but differ in their degree of saturation:
- Stearic Acid: This is a saturated fatty acid. It has no carbon-carbon double bonds, resulting in a straight chain that packs easily, making it a solid at room temperature.
- Oleic Acid: This is a monounsaturated fatty acid. It contains one 'cis' double bond, which creates a bend in its structure, making it a liquid.
- Linoleic Acid: This is a polyunsaturated fatty acid. It contains two 'cis' double bonds, which create more kinks in its structure, also making it a liquid with a lower melting point than oleic acid.
8. What specific role does oleic acid play in the human body, and why is it considered beneficial for health?
In the human body, oleic acid serves as a primary source of energy and is a fundamental component of nerve cell membranes (myelin) and other cell membranes, contributing to their fluidity and function. It is considered beneficial because substituting it for saturated fats in the diet can help lower LDL (low-density lipoprotein) or 'bad' cholesterol levels while potentially maintaining or increasing HDL (high-density lipoprotein) or 'good' cholesterol. This effect is a key reason why diets rich in oleic acid, like the Mediterranean diet, are associated with a reduced risk of cardiovascular diseases.
