Volatile Oils-Introduction for pharmacy students and graduates

VOLATILE OILS
Dr. Ahmed Metwaly
Associate Professor, Faculty of Pharmacy, Al-Azhar University

INTRODUCTION
▪ "Volatile oils" are odoriferous principals obtained mainly from different plant organs, and rarely from animal sources.
▪ They are described as "volatile" or "etherial" oils to indicate that they easily evaporate on exposure to air at room
temperature (volatile, from the Latin "volare" i.e. to fly).
▪ They are also known as "essential oils" after the Latin word "essentia", which means a liquid easily changed to a
gas and most probably because they represent the "essences" or odoriferous principals of the plants.
▪ They are generally mixtures formed of hydrocarbons and their oxygenated derivatives.
▪ They differ entirely from "fixed" oils in both chemical and physical properties.
▪ The importance of these aromatic substances lies in their wide application as therapeutic, flavoring or perfuming
agents. In addition, some of the components of these oils are used as starting material for semisynthesis of other
compounds.

Volatile oil vs Fixed oil
Property Volatile oil Fixed oil
Volatilization at ordinary temperature
Volatile Non-volatile
Steam Distillation Distillable Non-distillable
Solubility Soluble in organic solvents (ether, CHCl3) and alcohol of
different strengthes
Limited solubility in organic solvents, almost insoluble
in alcohol
Stain on filter paper Transient Permanent and greasy
Response to long exposure to air and
light
Resinification Rancidity
Composition Different types of hydrocarbons and oxygenated compounds Glyceryl esters of fatty acids
Nutritive value None Nutritive
Soap formation Negative Negative

Botanical sources:
▪ There are about 17,500 aromatic species. The genera producing volatile oils are distributed in a limited number of families
(over 90) of the phanerogams.
▪ Among families rich in volatile oils are the following: Pinaceae, Lauraceae, Rutaceae, Myrtaceae, Zingiberaceae, Apiaceae
(Umbellifereae), Lamiaceae (Labiateae), and Asteraceae (Compositeae).
▪ Volatile oils may accumulate in all types of vegetable organs, such as:
- Flowers, e.g. rose, bergamot, tuberose, and jasmine.
- Leaves, e.g. citronella, eucalyptus, and laurel.
- Barks, e.g. cinnamon and cassia.
- Woods, e.g. rosewood and sandalwood.
- Roots, e.g. vetiver.
- Rhizomes, e.g. turmeric and ginger.
- Fruits, e.g. anise, star anise, and allspice.
- Seeds, e.g. nutmeg and cardamon .
Animal sources:
Commercially available animal-derived essences are musk, musk-like products and ambergris. These
products are secretions produced by the animal to act either as attractants or protectants

▪ All the organs of a given species may contain essential oil, but the composition of the oil usually
varies with the site of its production in the plant e.g.
1. Cinnamon oil obtained from the bark of Cinnamomum zeylanicum is rich in cinnamaldehyde, while that
from the leaf contains mainly eugenol.
2. The bitter orange tree (Citrus auriantium) produces three different types of oils:
- "Bitter orange oil": from the fresh pericarp of the fruit,
- "Neroli oil": from the flowers, and
- "Petit grain oil": from the leaves, twigs and unripe fruits. These three essential oils have different
composition and consequently differ in aroma.
▪ They may be present free or in combination with:
1. Sugars; as the aglycone part of certain glycosides, or
2. Gums, resins or both and thus form oleo-gums, oleoresins or oleo-gum-resins.
▪ They usually accumulate in specialized histological structures, which are often located either on or near
the surface of the plant such as:
1. Oil cells: in family Lauraceae and Zingeberaceae.
2. Glandular hairs: in family Lamiaceae (Labiateae).
3. Secretory canals (tubes): in family Apiaceae (Umbellifereae).
4. Oil cavities (glands): in family Rutaceae and Pinaceae.

Physical properties
▪ Volatile oils have a number of common physical properties despite of their variable composition.
1. They are colorless, pleasant smelling liquids at ambient temperature, but they are also volatile (c.f. fixed oils).
2. They can be steam distilled (c.f. fixed oils).
3. They have a high refractive index and most of them are optically active.
4. Their density is mostly lower than that of water except for few ones.
5. They are immiscible with water, but sufficiently soluble to impart a distinct fragrance to water (aromatic
waters).
6. They are soluble in common organic solvents and lipids (liposoluble).
7. They may darken in color when exposed to light (due to resinification).
▪ Exceptions
1. Oil of lemon leaves on evaporation a non-volatile gummy residue.
2. Oils of cinnamon, cloves, sassafras and winter green are heavier than water.
3. Oils of anise and rose solidify just below room temperature (15 & 18 oC respectively) i.e. they may be solid in winter.
4. Oils containing azulenes are colored (e.g. oil of chamomile).
Their presence at the outer layers of plant organs facilitates their action as:
1. Protectants against predators: such as insects and fungi thus acting as insect repellents and antifungal.
2. Pollinators: attracting insects, thus playing an effective role during cross-pollination.

Chemical composition
▪ Practically, all volatile oils are complex and variable mixtures of constituents. Many types of hydrocarbons
and oxygenated compounds such as alcohols, ketones, aldehydes, ethers, oxides, phenols and esters are found.
Consequently, more than one constituent may possess physiological activity and they collectively give the odor of the
oil.
▪ Few oils may consist of one main component such as the volatile oil of mustard (93% allylisothiocyanate) and
oil of clove (85% eugenol).
▪ Constituents of volatile oils belong to two main groups of distinct biogenetic origin, the terpenoids (derived from
acetate) and the aromatic compounds (derived from phenylpropane), therefore, also called phenylpropanoids.
▪ Some essential oils contain degradation products of non-volatile constituents (e.g. furfural a degradation product
of carbohydrates).

PREPARATION OF VOLATILE OILS
The following methods are commonly used for preparation of volatile oils:
Expression method Extraction method Enzymatic hydrolysis
Distillation method
Water Distillation
Water and Steam
Distillation
Direct Steam
Distillation
Extraction with Volatile
Solvents
Extraction with Non-Volatile
Solvents
The Enfleurage Method
The Pneumatic Method
The Maceration Method
Sponge Method
Scarification Process
Expression of Rasping Process
Machine Processes

The method depends on:
1) The condition of the plant material.
2) The location of the oil in the plant.
3) The amount of the oil.
4) The nature of the constituents.
Principle of Distillation Methods
• Distillation at such high temperatures may cause either decomposition or polymerisation.
• The presence of water during distillation allows the process to be carried out at a temperature below 100oC.
• This is explained by Dalton’s law of partial pressure which states that:
“When two immiscible liquids are heated together, they will boil at a temperature below the boiling point of
either one”

Direct Steam Distillation
Water and Steam Distillation
Water Distillation
Fresh materials containing
sufficient moisture
Dried and fresh especially herbs
and leaves.
1) Dried e.g. powders.
2) Petals which may
lump with steam
Plant Material
H2O is completely absent.
Steam is forced through the
material which is placed on
perforated trays.
H2O is present in the still but
steam alone is in contact with
the plant material which is
placed on a grill
Material completely covered
with H2O
Mode of charging
Better when charging is even
Better when charging is even
Better when material moves
freely in H2O
Hydrodiffusion
Can be modified according to
plant condition and nature of
oil
About atmospheric
About atmospheric
Steam Pressure
Can be modified according to
plant condition and nature of
oil
About 100 oC
About 100 oC
Temperature
Distillation Methods

Direct Water Distillation
Water and Steam Distillation
Water Distillation
High
Good
Low
Rate of Distillation
The best if no lumping or
chanelling
Better since hydrolysis is
diminished
Relatively Low, since:
1) Esters may be
hydrolyzed.
2) Water soluble and high boiling point
constituents remain in the still.
Yield of Oil
* Oils of Pippermint
* Oils of Cloves and
Cinnamon
* Oil of Citronella
* Oils of terpentin
* Oil of rose
Commercial
preparations
1) Stills are more durable and
suitable for large scale
production.
2) Suitable for oils rich in
esters and high boiling point
constituents.
Hydrolysis is prevented since no
excessive wetting of material.
1) Low priced and portable still.
2) Could be carried near production area.
Advantages

1) Powders could not be used
since easy chanelling.
2) Superheated steam is not
used since it results in plant
drying therefore wet steam is
prefered.
Low yield
1) Burning of plant.
2) Not used for oils rich in
saponifiable, water soluble or high
boiling point constituents.
Disadvantages

Scarification and Expression Methods
Principle
These are mechanical procedures carried at room temperature and based on puncturing and/ or squeezing of
the plant material to liberate the oil, which is collected.
Applications
They are used for preparation of heat sensitive oils which are present in large amounts in outer peels of fruits
e.g. epicarps of Citrus fruits (Rutaceae), such as orange, lemon and bergamot.
Preparation and Purification of the oil
The peel (or zest) of Citrus fruits consists of two distinct layers:
▪ An outer colored zone rich in waxes and pigments and containing the oil glands,
▪ An inner white zone formed of pectin and cellulose.
The classical process includes:
1. Squeezing of the peel under a stream of water yielding an emulsion formed of essential oil, water, pectin,
cellulose, pigments and traces of waxes.
2. Removal of water, pectin and cellulose by centrifugation.
3. Removal of waxes by strong cooling (chilling) followed by filtration or decantation.
The two principal methods of scarification are:
1) The “Sponge Method"
2) The Ecuelle a piquer Method (Scarification).

Extraction Methods
Applications:
For delicate flowers e.g. Jasmine which contain either:
1) Small amounts of oils.
2) Oils which decompose by the action of heat (stem)
According to the solvent used, extraction methods can be sub-classified into:
A) Extraction by Volatile Solvent
e.g. Petroleum ether, n-hexane, Benzene.
The solvent should be:
a) Dissolves the oil with the least amount of impurities.
b) Dose not react with any of the oil constituents.
c) Has a low boiling point.
d) Leaves no residue on evaporation.

• Extraction by Volatile Solvent depends on using of volatile solvents of low boiling
points e.g. benzene, or hexane in a continuous extraction apparatus “Soxhlet”.
• The volatile oil solution obtained is then evaporated under reduced pressure,
where the volatile solvent will evaporate, leaving the volatile oil behind.

B) Extraction by Non-Volatile Solvent
This processes are used for preparation of natural flower oils producing perfumes.
Solvent used are:
1) Fats e.g. Lard and tallow.
2) Fixed oils e.g. Olive oil.
• For extraction of the flowers with non-volatile solvents
the following procedures are used:
A) The Enfleurage Method
B) The Pneumatic Method
C) The Maceration Method

"Enfleurage" process
This technique is applied in the South of France, in the city of Grasse, for the preparation of oil of jasmine.
•The equipment consists of a great number of glass plates closely arranged in a wooden frame (or chassis).
Flower petals
Absolute alcohol
(3 successive extractions) & Cooling
(to remove most of fat)
[Alcoholic solution of v. oil + pigments + traces of fats]
Evaporation or
Fractional distillation
Dilution with
water + NaCl
Absolute of Enfleurage
[Semi-solid, alcohol-free product
Volatile oil
Enfleurage product (Floral pomade)
[Fat saturated with oil]
Triple extract
+ Fat mixture
Lard & tallow 2:1

The Pneumatic Method:
• This method is similar in principle to the Enfleurage Method , and involves the
passage of a current of warm air through the flowers.
• The air laden with suspended volatile oil is then passed through a spray of melted fat
in which the volatile oil is absorbed.
The Maceration Method:
• The flowers are gently heated and rotated with melted fat “lard or fixed oil” until
complete exhaustion.They are then stained out, squeezed and the process is repeated
until a special concentration is reached.
• The oil-containing fat is allowed to cool and the oil can be obtained from the mixture by
successive extraction with alcohol.

Methods of Preparation of Volatile oils
Disadvantages
Advantages
Applications
Process
The use of high
temperature and
water may affect
constituents.
Cheapest
commercial
technique (as
regards apparatus,
solvents and source
of heat).
Suitable for dried and
fresh plant material rich
in volatile oils with
constituents mostly
unaffected by heat.
Distillation
High cost due to
need of high
number of workers.
1) Carried at room
temperature.
2) Yields oils with
more natural
odors.
Suitable for preparation
of oils present in large
amounts in outer peels of
fruits and rich in heat-
sensitive constituents.
Scarification
and
Expression
High cost due to
use of solvents and
or/ great number of
workers.
1) Carried at room
temperature.
2) Yields oils with
more natural
odors.
Usually for fresh
materials with heat-
sensitive oils present in
small amounts.
Extraction

Preparation of Volatile Oil After Enzymatic Hydrolysis
• Occasionally the volatile oil is found in the plant in a glycosidal form.
• The odoriferous substance is set free only by hydrolysis of certain odorless glycosides present in the plant.
• The following are examples of such oils:
1) Methyl Salicylate It occurs in a glycosidal form named “Gaultherin” in the leaves of Gaultheria procumbens.
OCH3
O
O-glu-xyl
OCH3
O
OH
H2O
+
Gaultherin Methyl salicylate
Gaultherase
+ glucose Xylose
+
2) Eugenol
• It occurs in glycosidal combination as “Gein” in Geum urbanum.
• Eugenol and glucose are produced upon hydrolysis.
O-glc
OCH3
H2O
OH
OCH3
Glucose
+ +
Gein Eugenol

3) Volatile Oil of Black Mustard
The oil of the black mustard is present in a thioglycosidal form named “Singrin”, which upon hydrolysis yields the volatile
substance “Allyl isothiocyanate”.
N C S
H2O
N
S
OSO3
−
K+
glc
Sinigrin Allyl isothiocyanate
+
4) Preparation of Vanillin
Glucovanillin glycosides, obtained from vanilla pods (Vanilla planifolia) Family Orchidaceae.
CHO
O-glc
OCH3
H2O
CHO
OH
OCH3
Glucose
+ +
Glucovanillin
(non-volatile)
Vanillin
(Volatile)
H2O
-glucosidase
5) Volatile Oil of Bitter Almond
Amygdalin glycoside obtained from kernels of bitter almonds
(Amygdala amara or Prunus amygdalus Family Rosaceae).
CH
H2O
CHO Glucose
+
+
Amygdalin
(non-volatile)
Benzaldehyde
(Volatile)
H2O
emulsin
O gentiobiose
CN
HCN
(Volatile)
+

Physical Methods for Examination of Volatile Oils
1) Odor
2) Solubility
3) Specific Gravity
4) Optical Rotation
5) Refractive Index

Storage of Volatile Oils
• Deterioration of volatile oils during storage is attributed to changes in their constituents.
• Reactions such as oxidation, polymerization, hydrolysis and interaction of functional groups should be avoided.
• They are enhanced by evaluation of temperature, oxygen, moisture, light and traces of metals.
Precautions before and during storage
1) Oils should be free from metallic impurities (Ovoid the use of iron containers during preparation).
2) Oils are dried over anhydrous Sodium sulphate to get rid of any traces of moisture.
3) Containers used for storage should be dark colored and tightly closed.
4) The oils are kept away from light, at low temperature and sometimes under CO2 or N2 (inert gases).

Chemistry of Volatile Oils
• Many volatile oils are complex mixture of different groups of chemical compounds.
• They are generally a mixture of hydrocarbon and related oxygenated compounds.
• On the other hand, some oils as oil of bitter almond “benzaldehyde” and oil of winter green “methyl salicylate”
consist mainly of one component.
• The hydrocarbons mentioned here are collectively known as “terpenes”. It is derived from the German word
“Terpentine” meaning turpentine.
• The formula “C10H16” is called now true terpenes.
• In practice the term “terpene” is applied to all the C10 isoprenoid compounds, including those containing oxygen.
• The molecule structure of terpenes, are built theoretically from “isoprene” unit.
• Each molecule is made up of the union of two or more isoprene units.
• These units are usually united in a “head to tail manner”.
CH3 CH3
OPP
Isoprene Unit (C5) "Active Isoprene"
Isopentyldiphosphate
1
2
3
4
1
2
3
4
5 5
Head
Tail
Myrcene

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