Terpenoids are the hydrocarbons of plant origin having general formula (C5H8)n. They are
also oxygenated, hydrogenated and dehydrogenated derivatives. Basically terpenoids are
volatile substances which give fragrance or aroma to plants. They are also known as essential
oils because they represent essence. They are mainly found in leaves and fruits of plants like
conifers, citrus and eucalyptus. The term ‘terpene’ was assigned to the compounds after
isolation of volatile liquid turpentine from pine trees. Volatile oils get vaporized or
evaporates upon exposure to air at normal or ordinary temperature, so they are termed as
etherel oil. Volatile oils generally occurs in plant families like Umbelliferae (examples
Coriander, Fennel), Zingiberaceae (Ginger), Myrtacea (Clove), Piperaceae (black pepper),
Rutaceae (Lemon, Orange) etc
GENERAL PROPERTIES OF VOLATILE OILS OR TERPENOIDS
1. They are colourless, fragrant liquids lighter than water and volatile in nature.
2. A few of them are solids e.g. camphor.
3. They are soluble in organic solvents, alcohol and fixed oils and usually insoluble in water.
4. They are open chain or cyclic unsaturated compounds having one or more double bonds.
5. They give addition reaction with hydrogen, halogen, acids, etc and addition products possess antiseptic properties.
6. They undergo polymerization and dehydrogenation.
7. They are easily oxidized nearly by all the oxidizing agents.
CLASSIFICATION OF TERPENOIDS
1. Monoterpenoids (C10H16) n=2
2. Sesquiterpenoinds (C15H24) n=3
3. Diterpenoids (C20H32) n= 4
4. Triterpenoids (C30H48) n=6
5. Tetraterpenoids (C40H64) n= 8
6. Pentaterpenes (C50H80) n=10
7. Polyterpenoids (C5H8)n >8
Types of Volatile Oils
1. Alcohol volatile oils Mentha, Cardamom, Coriander, Rose oil,
Sandalwood oil (Santalol).
2. Aldehyde volatile oils Cinnamon, Lemon peel, Orange peel, Citronella oil (Geraniol, Citronellal, Farnesol), Lemon grass oil, Bitter almond oil.
3. Ester volatile oils Gaultheria, Lavender, Mustard.
4. Hydrocarbon volatile oils Turpentine, Black pepper.
5. Ketone volatile oils Caraway (Carvone, Limonene), Spearmint, Buchu, Camphor, Musk, Civet oil.
6. Oxide volatile oils Chenopodium, Eucalyptus (Cineole).
7. Phenolic ether volatile oils Anise, Fennel, Nutmeg.
8. Phenol volatile oils Clove (Eugenol), Thyme.
CHEMICAL TEST
1. Volatile oil produces temporary stains when smeared on paper or cloth. The stain disappears after some time because the oil volatilizes.
2. Upon addition of Sudan III (alcoholic solution) to the thin section of volatile oil containing drug, red colour forms.
3. When few drops of Tincture alkana added on thin section of drug, red colour develops which indicates the presence of volatile oil.
EXTRACTION OF VOLATILE OILS
Steam distillation, solvent extraction or mechanical means like ecuelle and enfleurage
methods are employed for extraction purpose of volatile oils. These methods are as follows:
1. Hydro-distillation method: This method comprises of water distillation, water and
steam distillation and steam distillation. These techniques are used for extraction of
volatile oils from crude drugs. Hydro-distillation technique is used for fresh leaves
and steam distillation uses for subterranean parts.
2. Enfleurage method: This method uses for the extraction of flavouring agents and
perfumery. In this method, the fresh flowers (mainly petals) are taken and spreaded over layer of fatty material. Then it kept over fatty material for imbibition. After the
imbibition the fresh petals are placed on fat layer and exhausted petals are removed. This process continues until saturation of fat layer with volatile constituents. This
saturated fatty layer is extracted with lipid solvents.
3. Ecuelle method: This method is employed for citrus fruits which contains volatile principles. Here the oil containing ducts which contain oil cells are ruptured by mechanical means or manually. For this purpose special vessel are taken which
contain pointed projections. The raw material is twisted over the projections in clockwise direction which rupture the cell and oil comes out.
MENTHA (click here)
CLOVE (click here)
CINNAMON (click here)
CASSIA CINNAMON (click here)
FENNEL (click here)
CORIANDER (click here)