Volatile oily products obtained often by steam distillation of freshly cut plant parts carrying the odor or flavor of the plants are known as essential oils.
Occurrence of Essential Oils: Flowers, bark, leaves, wood, fruits.
Chemical Nature of Essential Oils: Are members of a large groups of compounds a derivatives of isoprene, 5 carbon diene (structure)
1. These compounds are not lipids but are odoriferous substances.
2. Hetero gellous compounds.
3. Consists of monoterpencs, sesquiterpenes (hydrocarbons) numerous oxygenated compounds of all classes.
4. It consist complex mixtures of compounds like aldehydes, ketones, esters, ethers, phenyls, terpenes, camphor and benzene derivatives some contain resins in solution are called oleoresins or balsams.
Properties of Essential Oils:
1. Pungent taste and odor
2. Nearly colourless when fresh.
3. They become darker after exposure to air.
4. They are optically active.
5. Soluble in alcohol, CS2s CC14 petroleum ether and fatty acids.
6. Insoluble in acid and water.
7. No residue remain on cloth or paper
Physiological Role of Essential Oils:
1. Make plant part unpalatable to animals or parasitic insects.
2. In flowers, they serve to attract insects for pollination.
3. Repel the harmful insects.
Uses of Essential Oils:
1. It is used as medicine, acts as a stimulator or antiseptic local irritant, flavoring food, beverages.
2. It is used in preparation of perfumes.
3. Attractant and herrce help in cross pollination.
Classification of Essential Oils:
Essential Oils are classified in 4 Major Groups
1. Aldehyde: Cinnamic aldehyde e.g. Oil of cinnamon, oil of casia.
2. Ester: Methyl ester of salicylic acid e.g. oil of winter green
3. Ether: Aromatic ether e.g. oil of clove
i. Lemonine (+ dexirorotatory) e.g. oil of lemon, oil of bitter orange laevorotatory oil of pine needle.
ii. Terpenoline cardamon oil.