This document provides an introduction to volatile oils. It defines volatile oils as odorous principles found in various plant parts that evaporate at ordinary temperatures. Volatile oils are mixtures of terpene hydrocarbons and their oxygenated derivatives that can be isolated from plants by distillation. They have many therapeutic uses and are also used in perfumes, cosmetics, foods and other industries. The document discusses the distribution of volatile oils in plants, their physical and chemical properties, isolation methods, classification based on chemical constituents, and importance.
1. Prepared by,
Dr. Preeti D. Verma
Lecturer, Department of Pharmacognosy
L. M. College of Pharmacy, Ahmedabad.
AN INTRODUCTION
TO VOLATILE OILS
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2. DEFINITION:
Evaporate at ordinary temperature, when exposed to
air – “Volatile” or “Ethereal Oils”.
Odorous principle found in various parts of plants.
Represent the „essence‟ or odoriferous constituent of
plant – “Essential Oils”.
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3. DISTRIBUTION:
Found in species of Families like Umbelliferae, Labiatae,
Piperaceae, Lauraceae, Rutaceae, Myrtaceae, Zingiberaceae,
Pinaceae, Compositae, etc.
Depending upon the plant family, the volatile oils may occur in
specialized secretary structures, like
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Family Specialized secretary structures
Umbelliferae (Fennel, Corainder) Oil tubes (Vittae)
Labiatae (Mint) Glandular trichomes
Piperaceae (Black pepper) Modified parenchymatous cells
Lauraceae (Cinnamon), Zingiberaceae
(Ginger,Turmeric)
Oil cells
Rutaceae (Orange, Lemon); Myrtaceae
(Clove, Eucalyptus), Pinaceae (Pines)
Schizogenous, Lysigenous,
Schizolysigenous passages
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The secretory cavities may arise by
separation of the cells & subsequent
formation of secretory epithelium,
which leads to the formation of
Schizogenous passage/cavities.
Eg: Eucalyptus.
Breakdown of cells forming a cavity
which is not bounded by definite
epithelial, forms Lysigenous passage.
Eg: Gossypium
Breakdown of the cells to form cavity
is followed by subsequent formation of
secretory epithelium, known as
Schizolysigenous passage.
Eg: Clove.
5. OCCURANCE:
It may be present in entire plant or in any part of plant.
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Plant Part in which volatile oil is present
Conifers All tissues
Rose Petals
Cinnamon Bark and leaves only
Umbelliferous fruits Pericarp only
Mint Glandular hairs of the leaves and
stem
Sandalwood Heartwood
Nutmeg Seed
Orange Rind of the fruit and flower petals
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FORMATION OF VOLATILE OILS IN PLANTS
In the plant body Volatile oils are formed directly from
protoplasm by decomposition of resinogenous layers of
the cell-wall or by hydrolysis of certain glycosides
(Mustard and Bitter almond).
7. PROPERTIES
(A) PHYSICAL PROPERTIES :
1. Colourless when fresh.
Volatile oils Oxidize and Resinify
(Darken in colour)
2. Possess characteristic odour
3. High Refractive Index.
4. Optically active (diagnostic value)
E.g. Natural Menthol : Optically active (Levorotatory),
Synthetic Menthol : Optically inactive (Racemic mixture)
E.g. Natural Camphor: Optically active (Dextrorotatory),
Synthetic Camphor : Optically inactive (Racemic mixture)
On long standing
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https://fssai.gov.in/dart/#spices-condiments
5. All the voltile oils are lighter than water (i.e. Sp. gr. < 1)
Exception: Clove oil (Sp. gr. > 1)
9. (B) CHEMICAL PROPERTY
Get oxidized and resinified by exposure to light or air or
oxidizing agents.
6. Solubility
(i) Immiscible with water, But sufficiently soluble to
impart their odour to water.
(ii) Soluble in organic solvents like alcohol, ether,
acetone, chloroform, etc.
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10. Identification Tests:
1. They do not leave a permanent stain on paper.
2. Chemical test for some specific chemical constituents like
ester, alcohol, etc:
a. Thin T.S. of drug + Alcoholic solution of Sudan Red III :
Red colour (oil globules).
b. Thin T.S. of drug + a drop of tincture Alkane: Red colour.
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• Storage: Volatile oils are stored in air-tight
containers (preferably fully filled) in cool and dry
place in amber-colored glass containers.
11. CHEMISTRY OF VOLATILE OILS
All Volatile oils are mixtures of Terpene Hydrocarbons &
oxygenated derivatives of these hydrocarbons, with the
Exception of Glycosidic Volatile oils (Eg: Bitter almond oil &
Mustard oil),
Usually, Terpene hydrocarbons are Aliphatic in nature while
their oxygenated derivatives are usually Aromatic in nature.
The characteristic odour, taste and therapeutic properties of
volatile oil is mainly determined by the oxygenated constituents,
which to some extent ares soluble in water, but more soluble in
alcohol.
In certain oils (e.g. Turpentine oil), Terpene hydrocarbon
predominates with limited amount of oxygenated derivatives,
while in some oils (e.g. Clove & Cinnamon oil), the oxygenated
derivatives predominates.
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12. Terpene/Terpenoids/Isoprenoids:
Composed of Isoprene units (C5H8), which are derived from
Acetate Mevalonate Pathway.
Isoprene units are branched chain, 5-carbon units compounds
with 2 double bonds.
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Name No. of
isoprene
units
Molecular
formula
Monoterpenes 2 (C5H8)2
Sesquiterpenes 3 (C5H8)3
Diterpenes 4 (C5H8)4
Triterpenes 6 (C5H8)6
Polyterpenes n (C5H8)n
Isoprene unit
13. Volatile oils:
Terpenes which are mainly present in volatile oils are:
Monoterpenes (Largely) and closely related are Sesquiterpenes,
sometimes diterperpenes.
Terpenes present in volatile oil may be either
Acyclic/Monocyclic/Bicyclic in nature.
o Acyclic Monoterpenes – e.g. Geraniol
o Monocyclic Monoterpenes – e.g. Limonene
o Bicyclic Monoterpenes – e.g. α-Pinene
o Monocyclic Sesquiterpenes – e.g. Zingiberene
o Bicyclic Sesquiterpenes – e.g. Cadinene, β-Caryophyllene
Oxygenated derivatives of existing Terpene Hydrocarbon may
vary in their chemical nature & they may be either Alcohol,
Ketone, Aldehyde, Ester, Phenol, Oxide, etc.
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Geraniol Limonene
. α-Pinene
β-Caryophyllene
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Volatile oils:
Another major group of volatile oil constituents are: Phenyl
propanoids (aromatic in nature), that are compounds with
phenyl ring & a propane side chain. [C6 – C3 compound],
aromatic compound formed via shikimic acid-
phenypropanoid pathway.
Eg: Eugenol, in clove oil is a Phenylpropanoid.
Eugenol
C6
C3
16. CLASSIFICATION
Based on the chemical constituents.
A. Volatile oils with Terpene Hydrocarbons
E.g. Turpentine oil.
B. Volatile oils with Oxygenated derivatives of Terpene
Hydrocarbons
C. Glycosidic Volatile oils
E.g. Mustard oil, Bitter Almond oil, Gaultheria oil.
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Eugenol
(Clove)
Cinnamaldehyde
(Cinnamon)
Menthol
(Mentha)
Carvone
(Dill)
Identify the type of volatile oil from the functional groups present in the following
structures:
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Anethole
(Fennel)
Methyl salicylate
(Gaultheria)
Cineole
(Eucalyptus
&
Cardamom)
Identify the type of volatile oil from the functional groups present in the following
structures:
20. C. Glycosidic Volatile oils
They are obtained by enzymatic hydrolysis of some glycosides
E.g. Mustard oil (Sinigrin ), Bitter Almond oil, Gaultheria oil.
They are further divided into:
A. Terpenoidal Glycosidic Volatile oils:
Certain terpenes occur as glycoside. E.g. Thymol & Carvacrol
occur as glycoside in volatile oil of Thymus vulgaris.
b. Non-terpenoidal Glycosidic Volatile oils:
E.g. Organic sulphides like Allicin of Garlic
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23. IN INDUSTRIES:
• As Perfumery (Aroma), In Cosmetics, Incense sticks.
IN FOOD & PHARMACEUTICAL INDUSTRIES
• As Flavour.
• Insect-repellant, insecticides and pesticides.
• Deodorants.
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Methods for isolation the volatile oils from the crude
drugs
(i) Extraction method (Use heat/steam): Distillation
(a) Water Distillation
(b) Water-Steam Distillation
(c) Direct-Steam Distillation
(ii) Expression method (cold method)
(a) Ecuelle-pierce method
(b) Enfluerage
(iii) Extraction with volatile organic solvents (cold
method)
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Clavenger’s Apparatus
(for water distillation)
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Ecuelle pierce method
(oil from citrus fruit rinds)
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Enfleurage
(oil from delicate flower petals)
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31. DIFFERENCES BETWEEN
VOLATILE OILS AND FIXED OILS
Volatile Oils Fixed oils
1.
They are Volatile - Evaporate
at Room temperature.
Non-Volatile – Do not evaporate
at Room temperature.
2.
Chemically, they are
Terpenoids (C5H8)- made up
of mainly Monoterpene and
Sesquiterpenes.
Esters of Glycerine and long-
chain Fatty acids.
3.
Do not leave permanent stain
on paper or cloth.
Leave permanent stain on paper
or cloth.
4.
Can be distilled (Isolated by
Distillation method).
Cannot be distilled (Isolated by
Expression method).
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32. 5.
Have very low food value
(Calorific value).
Have high Calorific value – Used
as dietary supplement (Cod-liver
oil).
6.
Cannot be saponified by
Alkali.
Can be Saponified by Alkali
(undergo saponification)
7.
Oxidize or Resinify on
storage, but do not get
racid.
Turn Rancid on storage, due to
free acidity (Rancidity occurs)
8.
E.g.
Peppermint oil,
Eucalyptus oil, Cumin,
Caraway, Lemongrass,
Ajowan oil, etc.
E.g.
Castor oil, Almond oil,
Coconut oil, Groundnut oil,
Cod-liver oil, Shark- liver oil, etc.
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