3.Role in plants
6. Chemical constituents
7. Methods of obtaining
8. Volatile oil Vs. Fixed oil
10. How it use
They evaporate when exposed to the air
at ordinary temperatures so they are
called volatile oils, ethereal oils or
They are called essential oil because
volatile oil represent the essences of
Significance of volatile oil
As spices and condiments
Manufacture of perfumes, soaps, cosmetics
Role of volatile oils in plants
Due to disagreeable taste and odor, they
protect the plants from grazing animals
In flowers, they attract the insects for
Properties of volatile oils
• Characteristic odors
• High refractive index
• Optically active
• Immiscible with water
• Soluble in ethers, alcohol and
most organic solvents
1.Hydrocarbon volatile oils
It has been observed that terpene
hydrocarbons usually occur in most of the
volatile oils obtained from natural sources. They
may be further classified into three categories,
(a) Unsaturated acyclic hydrocarbons,
(b) Aromatic hydrocarbons, and
(c) Alicyclic hydrocarbons.
Ex: Turpentine – pinene , carene , limonene
2.Alcoholic volatile oils
A good number of alcohols occur abundantly in a
plethora of volatile oils, which may be judiciously
classified into the following heads, namely:
(a) Acyclic (aliphatic) alcohols,
(b) Monocyclic (aromatic) alcohols,
(c) Alicyclic (terpene and sesquiterpene) alcohols.
Ex: 1. Peppermint- Menthol
2. Cardamom- Borneol
3. Coriander- Coriandrol (Linalool)
4. Rose- Nerol
5. Sandalwood- Santola
3.Aldehydic volatile oils
Aldehydes provide a soapy-waxy-lemony-
floral effect to the formula and are used to
classify a fragrance as "aldehydic".
1. Cinnamon - Cinnamic aldehyde
2. Lemon peel - Citral
3. Orange peel - Citral
4. Citronella - Citronellal
5. Lemon grass - Citronellal
4.Ketonic volatile oils
The ketones that invariably occur in volatile oils may
in the following two categories, namely:
(i) Aliphatic ketones, and
(ii) Aromatic Ketones.
Ex: Caraway- Carvone , Spearmint- Carvone ,
Vetiver- Vetivone , Fennel- Fenchone
5.Phenolic volatile oils
The important drugs containing phenol volatile
oils are, namely: Clove oil, Myrcia oil (Bay oil),
Organum oil, Pinetar, Thyme etc. In fact, they
essentially owe their value in the pharmaceutical
domain almost exclusively by virtue of their
antiseptic and germicidal properties of
their phenolic constituents. A good many of
them are employed as popular flavouring
The phenols are classified into the following
(i) Monohydric phenols and
(ii) Dihydric phenols.
Ex: Clove – Eugenol , Ajwon – Thymol
6.Phenolic ether volatile oils
Phenolic ether occurs in volatile oils such as
anethol from anise and fennel, Safrole from
Ex: Anise , Fennel – Anethol , Nutmeg -
7. Oxide volatile oils
It contains colourless or pale yellow oil which is
about 6%, having an aromatic odour, spicy
cooling taste, containing 70% of cineole
C10H18O, d- pinene and other terpenes,
resins, a bitter principle and tannin, eucalyptic
acid, Ca-oxalate etc.
Ex: Eucalyptus – Cinole (eucalyptol)
8. Ester volatile oils
A wide variety of ester occurs in volatile oils. The
most common are the acetates of terpineol
borneol and geranial. Other examples of esters in
volatile oils are allyl isothiocyanate in mustard oil
and methyl salicylate in wintergreen oil.
Ex: Gaultheria(Wintergreen) – Methyl salicylate
Chemical constituents of volatile oil may be
classified into two groups.
Natural products whose structures may be divided into
These units arise from acetate via mevalonic acid.
These are branched chain 5 carbon units containing 2
Made up of head to tail condensation of isoprene units.
i. 1 isoprene unit present= hemiterpene (C5H8)
ii. 2 isoprene unit present= monoterpenes (C10H16)
iii. 3 isoprene unit present= sesquiterpene (C15H24)
iv. 4 isoprene unit present= diterpene (C20H32)
v. 6 isoprene unit present= triterpene (C25H48)
Majority of the terpenes are monoterpenes in volatile
They are formed via shikimic acid
These compounds contain phenyl ring with an
attached propane side chain.
Many of the Phenylpropanoids found in
volatile oils are phenols or phenol ethers.
Methods of obtaining volatile oils
The method of obtaining volatile oils depends
upon the condition of plant materials.
Oil production can be divided into three major
ii. Solvent extraction
iii. Mechanical expression
Specialized methods are:
i. Ecuelle Method
iii. Destructive distillation
Difference between volatile oil
and fixed oil
Evaporate from source when
exposed to room temperature.
Color less liquid, or crystalline
or amorphous solid.
Do not form permanent stains
Do not rancidify.
Having distinct odor.
Can be distilled from natural
On exposure to air and light,
they oxidize and resins are
Remain fixed on the source
when exposed to room
Some of these oils possess
colors i.e. castor oil, shark liver
Form permanent stain on paper.
Rancidified on exposure to air.
May or may not possess odor.
Can not be distilled.
On exposure to air or light, it
becomes rancid developing a
Can not be saponified.
Mixture of mono
Immiscible in water but
soluble in alcohol.
Can be saponified.
They are esters of glycerol
with long fatty acid chain.
Soluble in water, sparingly
soluble in cold alcohol.
Difference between volatile oil
and fixed oil
USES OF VOLATILE OILS
Therapeutically (Oil of
Flavouring (Oil of Lemon)
Perfumery (Oil of Rose)
Starting materials to
synthesize other compounds
(Oil of Turpentine)
Anti-septic – due to high
phenols (Oil of Thyme). Also
as a preservative (oils interfere
with bacterial respiration)
Lemon balm, Rosemary,
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