Terpenoids: Menthol, Citral and Artemisinin – a comprehensive guide(1)


Terpenoids are also known as terpenes, are a large and diverse class of organic compounds produced by various plants, fungi and animals. Terpenoids are hydrocarbon of plant origin(naturally) of the general formula (C5H8). They are available in volatile oil like menthol, citral, artemisinin.

Properties of terpenoids

Terpenoids: Menthol, Citral and Artemisin

1. It is a colorless substance.
2. They are soluble in organic solvents like alcohol and ethanol but insoluble in water.
3. Most of the terpenoids are optically active.
4. They really get oxidized by oxidizing agents.
5. They undergo polymerization and dehydrogenation in the ring.

Uses of terpenoids

1. It is used in analgesic, carminative and antiseptic.
2. It is used for perfumery and also as a flavouring agent.
3. It act as precursor for this synthesis of B-ionine, which further used for synthesis of vitamin A.
4. It is also used in the preparation of soap, cosmetics, perfumery & food articles.
5. It is also used in pesticides and insecticides.

Some drugs of terpenoids

1. Menthol

Menthol is primarily found in mint oils, such as peppermint and spearmint. It provides the characteristic cooling sensation and minty aroma. Family of menthol is Labiatae. It is freely soluble in alcohol, chloroform, ether, petroleum ether.

Extraction and isolation of menthol

1. Take the accurately weight quantity is coarse powder of mentha piperita parts just before flowering.
2. Extract the peppermint oil by water distillation method.
3. Take fresh air dryer mentha plants and allow it into steam distillation.
4. The mixture vapour is generating which further pas through condenser.
5. Now both vapour is cooled and back to liquid form.
6. Mentha oil is floated on the top of water due to lighter than water which further separate out through separator.
7. Now Mentha oil is filtered and allow it to cool; crystal and menthol will separate out.

Analysis of menthol

Sample preparation: 1 mg of menthol of dissolve in 1ml of menthol.
Standard sample: menthol
Stationary phase: silica gel-G
Mobile phase: pure chloroform
Detecting agent: 1% vanillin-sulphuric acid reagent and heat the plate at 110°C for 10 minutes.
Rf value: 0.48-0.62.

2. Citral

Citral is a terpenoids aldehyde. It has to isomeric forms: generarial and neural. The chemical formula for both isomers is C10H160. Citral is found in the essential oils of citrus fruits, lemongrass, lemon myrtle, and Litsea cubeba. It contributes to the citrusy aroma and flavour of these plants.

Extraction and isolation of citral

1. The fresh plant material is hydro-distilled to obtain lemon grass oil.
2. Purification by fractional crystallization.
3. To the total oil, first sodium sulphite is added the citral get converted into its sulphite salts.
4. The salt crystallize out of the solution.
5. The crystals are filtered and washed with ether or chloroform.
6. The product is then subjected to sodium carbonate treatment to recover citral.

Identification and analysis

T.L.C method – dissolve 1mg of citral in 1ml of menthol.
Stationary phase – silica gel-G
Standard sample – citral
Detecting agent – 2, 4, dinitrophenyl hydrazine reagent to produce yellow to orange colour.
Mobile phase – pure chloroform
Rf value – 0.51

3. Artemisinin

It is also called artemisinin. Artemisinin is derived from the plant Artemisia annua, also known as sweet wormwood. It has been used traditionally in Chinese medicine for the treatment of fever and malaria. Artemisinin is a sesquiterpene lactone. It’s chemical formula C12H22O5. It contains a unique peroxide bridge. Family of artemisinin is Compositae.

Extraction and isolation of artemisinin

1. The leaves are air dried, coarsely powdered and extracted with petroleum ether.
2. The extract is concentrated, dried and re-dissolved in chloroform. Add acetonitrile to precipitate sugars and waxes.
3. Filter and collect the filtrate. Evaporate to dryness to yield.
4. The chromatographic fractionation of concentrate on silica gel by eluting with chloroform-ethyl acetate yield the fraction of artemisinin.
5. The fractions containing artemisinin could be crystallized from cyclohexane or 50% ethanol.

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