INTRODUCTION
 Crude drugs (herbs) & galenical products or
phytomedicinals are widely used in "complementary
medicine " [about 50% of the total drug market].
 "Pharmacognosy" = "knowledge of drugs" gives "a
scientific description of natural materials used in
medicine (herbs, animal products & inorganic
materials)".
 "Phytochemistry"
studies
"the
chemistry,
distribution, isolation, identification, quantitative
determination,
biosynthesis,
metabolism
&
biological activity of plant constituents."
Role of natural products in
modern medicine

Useful drugs which cannot be commercially
produced by synthesis e.g. opium, ergot &
cinchona alkaloids, digitalis glycosides & most
antibiotics.

Basic compounds, which could be modified to be
more effective or less toxic e.g. morphine
molecule.

Models for production of synthetic analogues with
similar physiological activities, e.g. procaine.

Starting materials for production of potent drugs
e.g. hydrocortisone & steroidal hormones from
stigmasterol & saponins.
Different forms of plant products
Different forms are supplied based on:
♣ Aim of use
♣ Nature of active ingredients
♣ Economic factors
1. Fresh plant materials [especially in perfume industry].
2. Dried plant materials: [flavoring agents, spices & drugs
where dosage is not critical].
3. Acellular products : materials derived directly from plants
[gums, resins, & fixed & volatile oils].
4. Galenical preparations: [plant extracts & tinctures]
5. Processed extracts : standardized to contain a certain
concentration of the active principle.
6. Pure compounds : most required in pharmaceutical
formulations as they facilitate proper standardization of
biological activity & quality control
Primary & secondary plant metabolites
Plant metabolites : organic substances formed
& accumulated by plants.
1. Primary metabolites : essential for life & present in
all organisms e.g. carbohydrates, proteins, fats, &
nucleic acids
2. Secondary metabolites: formed as a defense
against predators, attractants (volatile or colored)
or detoxifying agents. Mostly pharmacologically
active & found in specific organisms or group of
organisms.
Some metabolites could be included in both divisions
e.g. certain fatty acids & sugars.
Nomenclature of plant constituents
Systematic nomenclature is difficult due to complexity
of structure. Naming is based on trivial nomenclature.
Root names are derived from:
1. Name of the discoverer e.g. Pelletierine alkaloid
after Pelletier
2. Common name of the plant e.g. vinca alkaloids,
(vincristine & vinblastine), ergot alkaloids
(ergometrine & ergotamine)
3. Latin name of the plant e.g. visnagin from Ammi
visnaga & digitoxin from Digitalis lanata
4. Biological action e.g. emetine alkaloid which
produces emesis
Classification of plant constituents
Plant constituents occur as:
Single chemicals e.g. glycosides &
alkaloids ……..
Mixtures of compounds e.g. gums,
fixed oils, fats, waxes, volatile oils,
resins & resin combinations.
Classification of plant constituents
may be according to:
A. Pharmacological activity [analgesics,
laxatives, cardiotonics etc……..]
B. Biosynthetic
origin,
solubility
properties & key functional groups
C. Chemistry
properties
&
common
physical
B.According to biosynthetic origin, solubility
properties & key functional groups:
1.
2.
3.
4.
5.
6.
Phenolics: e.g. flavonoids & their glycosides,
phenyl propanoids, anthocyanins, xanthones,
tannins & quinones
Terpenoids: e.g. carotenoids, steroids & the major
constituents of volatile oils
Organic acids & lipids: e.g. simple organic acids
(citric, oxalic & ascorbic), fatty acids (in the form
of esters in fixed oils, fats & waxes)
Nitrogenous compounds: e.g. alkaloids &
cyanogenic glycosides
Water-soluble carbohydrates & their derivatives:
e.g. monosaccharides, oligosaccharides & watersoluble glycosides
Macromolecules: e.g. proteins & polysaccharides
C.According to chemistry & common physical
properties
This classification will be adopted
convenience, the major groups are:
for
1.Volatile oils, Resins & Resin combinations
2.Carbohydrates
3.Bitter Principles
4.Tannins
5.Alkaloids
6.Glycosides
VOLATILE, ETHEREAL or ESSENTIAL OILS
 "Volatile" or "ethereal": as they easily
evaporate on exposure to air at room
temperature (volatile, from the Latin "volare"
i.e. to fly & ethereal = ether-like in their
volatility)
 "Essential": as they mostly represent the
"essences" or principal active principles of
the plants in which they occur.
They differ entirely from "fixed oils“ in both
chemical & physical properties.
Major Differences between volatile & fixed oils
Property
Volatile oil
Fixed oil
Volatilization at
ordinary
temperature
Volatile
Non-volatile
Solubility
Soluble in organic
solvents (ether,
CHCl3) & alcohol
Limited solubility in
organic solvents,
almost insoluble in
alcohol
Stain on filter paper
Transient
Permanent &
greasy
Composition
Complex mixtures
of hydrocarbons &
oxygenated
compounds
Triglycerides of
fatty acids e.g.
palmitic, stearic,
oleic……..
Response to long
exposure to air &
light (oxidation)
Resinification
Rancidity
Saponification with
caustic alkali (KOH)
Negative
Positive
Historical
 In ancient Egypt: embalming process (antibacterial
properties of essential oils & resins).
 In the Roman culture: aromatic essences in
massage & baths.
 Incenses: [in temples, churches & mosques] consist
of resins rich in volatile oils
 In folk medicine: inhalation of aromatics as
tranquilizers (e.g. incenses in case of irritability) or
stimulants (e.g. onions in case of fainting)
Distribution & Occurrence
Animal sources:
Botanical sources:
 Musk,
musk-like
products
(civet,
castoreum)
&
ambergris
 Mainly in higher plants
 Secretions produced
for
attraction
or
protection
 Especially in Pinaceae,
Lauraceae, Rutaceae,
Myrtaceae, Labiateae,
Zingiberaceae,
Umbellifereae, &
Compositeae.
Free & Combined Forms of Volatile Oils
They may be present :
1. Free  aromatic characteristic odor, or
2. Combined with:
 Sugars  glycosides
 Gums, resins or both  oleo-gums,
oleoresins or oleo-gum-resins.
Location in the plant
They may be:
 Diffused in all plant tissues (e.g. Pinaceae, Conifers)
 Accumulated in specialized secretory structures
usually on or near the surface of the plant e.g.:
1.
Modified parenchyma or oil
(Lauraceae & Zingiberaceae)
cells:
2.
Glandular hairs: (Labiateae)
3.
Oil tubes or Vittae: (Umbellifereae)
4.
Oil glands: (Rutaceae & Pinaceae)
Distribution in plant organs
V. O. may accumulate in all types of
plant organs:
 Flowers e.g. rose
 Leaves e.g. eucalyptus & peppermint
 Barks e.g. cinnamon
 Woods e.g. sandalwood
 Roots e.g. vetiver
 Rhizomes e.g. ginger
 Fruits e.g. umbelliferous & citrus
 Seeds e.g. cardamon
Variation in composition of v. oils from
different organs of the same plant
1.
Cinnamon tree:
 bark oil rich in cinnamaldehyde
 leaf oil rich in eugenol
 root oil rich in camphor
2. Bitter orange tree:
 "Bitter orange oil": from the fresh pericarp of the
fruit (rind or zest),
 "Neroli oil": from the flowers
 "Petit grain oil": from the leaves, twigs & unripe
fruits.
These oils are different in composition & aroma
Physiological role of V.O. in the plant
1. Waste products of metabolism (detoxifying
agents)
2. Energy producers in case of deficiency
from CO2 assimilation
3. H+ donors in certain metabolic reactions
4. Protectants against predators: e.g. insect
repellents & antifungals (i.e. for defense).
5. Pollinators: attracting insects during crosspollination (due to their nice odors).
Common Physical Characters
1. Colorless, pleasant smelling liquids,
volatile at room temperature
2. Steam distillable
3. High refractive index
4. Mostly optically active
5. Density < water (i.e. lighter than water)
except for few ones
6. Immiscible with water, but sufficiently
soluble to impart a fragrance to water 
aromatic waters [hydrosols]
7. Soluble in alcohol & common organic
solvents
8. Darken in color if exposed to air & light
(resinification)
Exceptions
1. Oils of cinnamon, clove & winter
green are heavier than water
2. Oils of anise & rose solidify just below
room temperature (15 & 18oC,
respectively)
3. Oils containing azulenes are colored
(e.g. oil of chamomile is blue).
Chemical Composition
 V. O. are complex mixtures of hydrocarbons &
oxygenated compounds [alcohols, phenols,
ethers, aldehydes, ketones, oxides, peroxides &
esters]. All of these contribute to the odor &
physiological activity of the oil.
 Few oils consist of one main component e.g.
1. Oil of mustard (93% allylisothiocyanate)
2. Oil of clove (85% eugenol)
 Most V. O. constituents belong to 2 main groups:
1. Terpenoids [derived from acetate] &
2. Phenylpropanoids
[aromatic
derived from phenylpropane]
compounds,
Variation in Physico-Chemical
Characteristics
Most important influencing factors are:
The environmental conditions under
which the plant is grown
The method used for preparation of
the oil
Medicinal & Commercial Uses of V.O.
1.
Therapeutic & medicinal uses: local stimulants,
carminatives, diuretics, mild antiseptics, local irritants,
anthelmintics, parasiticides …
2.
Spices & condiments: in food seasoning (to impart aroma
& flavor) or as preservatives
3.
Flavoring agents: in food (e.g. beverages, soups, bakery
products, confectionery) & pharmaceutical industries
4.
Aromatic agents: in all types of perfume industries
(cosmetics, soaps, deodorizers, household cleaners,
polishes & insecticides)
Methods of Preparation of Volatile Oils
Distillation
Scarification & Expression
Water Distillation
Sponge Method
Steam Distillation
Ecuelle a piquer
Method
Water & Steam
Distillation
Direct Steam
Distillation
Extraction
Enzymatic
Hydrolysis
Extraction with Volatile
Solvents
Extraction with Non-Volatile
Solvents
Expression of Rasping Process
Enfleurage Method
Machine Processes
Pneumatic Method
Maceration Method
Selection of the suitable method is done
according to :
1. The condition of the plant material (moisture
content, degree of comminution)
2. The localization of the oil in the plant (superficial or
deep)
3. The amount of the oil
4. The nature of the oil constituents
Distillation methods
Principle
 Most volatile oil constituents boil between 150300ºC. In order to reduce decomposition, volatile
oils are distilled in the presence of water.
 The mixture will boil below 100ºC [Dalton’s law of
partial pressure : “When 2 immiscible liquids are
heated together, they will boil at a temperature
below the boiling point of either one”].
 The oil is carried over with steam in the form of
vapor
Distillation methods
Application:
preparation of thermostable oils,
present in large amounts & not rich in esters (e.g.
oils of turpentine, peppermint, cardamon, anise,
eucalyptus)
Types of distillation:
1. Water-distillation
2. Steam distillation
 Water-and-steam distillation
 Direct-steam distillation
Distillation: Terminology
 Hydrodiffusion = process by which water or steam
penetrates the plant tissues to take over the oil
 Aromatic water = Hydrosols = distilled aqueous
layer saturated with oil e.g. rose, orange flower &
peppermint waters
 Cohobation = return of aromatic water to the
distillation chamber, in water distillation, in order to
recover the dissolved oil.
Distillation methods
Steam Distillation
H2O Distillation
H2O & Steam
Direct Steam
Plant material
Dried & fresh (petals),
not injured by boiling
with H2O
Dried & fresh,
injured by direct boiling
with H2O
Fresh ( i.e.
moisture)
Commercial
preparations
Oils of turpentine &
rose
Oils of clove, cinnamon
& citronella
Oil of peppermint
-H2O present but not in
contact with the plant.
-Steam is generated in
the still & penetrates the
drug
-Dried
material
is
moistened
before
charging
-H2O is absent.
Mode of charging Plant material dipped
in H2O
Steam pressure
Temperature
containing
-Steam is introduced by
pipes & forced through the
plant material placed on
perforated trays
 atmospheric
Can be modified
 100ºC
Can be modified
Rate & yield
Relatively low
Better
The best
Advantages
-Least expensive
Hydrolysis is reduced
-Cohobation is allowed
Method suitable for oils rich
in esters & high b. p.
constituents
-Esters are hydrolyzed.
-H2O sol. & high b.p.
constituents are not
distilled
-Not suitable for powders, efficient if material entire or
crushed
-Hydrodiffusion may be reduced due to lumping or
channeling
Disadvantages
Distillation apparatus
Consists of 3 parts:
1. The distillation chamber
made of stainless steel
free from any Fe+++ ions
to avoid degradation of
the oil constituents 
darker oils.
2. The condensing system
3. The receiver
e.g.
Florentine
receivers
which allow separation
of the oily layer from
water in the distillate
(oils lighter or heavier
than water)
Florentine Receivers
Purification (Rectification)
of distilled oils
Bad smelling or dark
colored oils are purified
by:
1.
Redistillation or dry
distillation
under
reduced pressure
2.
Dehydration by passing
over anhydrous sodium
sulphate
Remarks
1. Distillation should be done just after comminution [ i.e. reduction
in size, crushing, powdering)  prevent loss by evaporation or
deterioration of the oil.
2. Coarse comminution  increase "Hydrodiffusion"  oils with
better yield & quality.
3. High temperature & water  distilled oils differing in composition
from natural oils [artifacts].
4. Insufficient distillation time (shorter)  fractionation of the oil.
5. Hydrolytic products (e.g. lower alcohols & acids) are watersoluble & remain in the distillation chamber.
6. Steam volatile impurities e.g. amines & furfural (degradation
product of carbohydrates) contaminate the final product.
7. Sensitive constituents could be affected by boiling water e.g.
 Esters  hydrolyzed.
 Tertiary alcohols  dehydrated  hydrocarbons.
 Unsaturated hydrocarbons  polymerized.
Scarification & Expression Methods
Principle
Mechanical procedures carried at room
temperature & based on puncturing &
squeezing of the plant material to
liberate the oil, which is collected.
Applications
Preparation of heat sensitive oils, present in large
amounts in outer peels of fruits e.g. Citrus fruits
(Rutaceae) as orange, lemon & bergamot.
Scarification & Expression Methods
The peel of Citrus fruits consists of 2 distinct layers:
1. Outer colored zone (waxes + pigments + oil glands)
2. Inner white zone (pectin + cellulose).
Scarification & Expression Methods
The process involves 3 steps:
1. Squeezing of the peel under a stream
of water  emulsion (volatile oil +
water + pectin + cellulose + pigments
+ traces of waxes).
2. Centrifugation (to remove water +
pectin + cellulose)
3. Strong cooling (to remove waxes)
Scarification & Expression Methods
A- Sponge Method
Based on squeezing the removed peels e.g. orange
1. Fruits washed, cut into halves & fleshy parts removed.
2. Peels soaked in water, turned inside out then pressed
between a convex projection & a sponge.
3. Sponge (saturated with oil emulsion) periodically squeezed in
a vessel
The tissue of the sponge serves for:
1. Collection of the oil
2. Filtration of the product from any particles of the inner white
zone of the peel.
Scarification & Expression Methods
B- Ecuelle-à-piquer method
 Based on puncturing (scarifying) the surface of whole fruits
(lemon), the oil exudes from the outer zone of the peels in the
form of emulsion.
 The instrument is funnel-shaped, formed
of a shallow bowl with a tubular
projection at the center. The bowl bears
numerous pins which scarify the oil
glands to release the oil.
 The tubular part serves as:
1. Handle to rotate the instrument.
2. Receiver to collect the oil.
Scarification & Expression Methods
C- Expression of rasping process
 Based on removal of the outer layer of the peel
with a grater, collecting the rasping in special
bags then strong pressing.
 The oil emulsion is collected in large vessels
D- Machine processes
 Based on the same principles as the above 3
traditional methods A, B & C but carried out by
machines.
Solvent extraction methods
Principle
Based on extraction of the volatile oil from the
plant material with a suitable solvent
According to the nature of the solvent used,
three types are distinguished:
1. Volatile solvent extraction
2. Non-volatile solvent extraction
3. Supercritical fluid extraction
Solvent extraction methods-Application
Preparation of delicate flower
oils
e.g.
jasmine,
violet,
tuberose & narcissus which are:
1. Present in very small
amounts,
not
easily
obtained by distillation or
expression
2. Oils formed of thermolabile
constituents (i.e.
easily
decomposed by heat)
Volatile solvent-extraction
Preparation of "floral concretes"
1. Solvents used: petroleum ether & n-hexane
2. Extraction (“percolation” or “maceration” at room temperature,
“continuous hot extraction” in a Soxhlet apparatus at constant
temperature)
3. Solvent removal (distillation under reduced pressure)
Percolator
Soxhlet apparatus
Volatile solvent-extraction
Floral concrete = Fragrant constituents + Fats +
Waxes + Albuminous matter + Fat soluble pigments
e.g. "floral concrete" of jasmine is semi-solid &
yellowish-orange in color.
Floral absolute = consists mostly of the oxygenated
constituents of the oil.
 More expensive & purified than the corresponding
concrete.
 Preparation: repeated extraction with absolute alcohol
 Impurities: removed by strong cooling & filtration
 Solvent removal : by distillation.
Non-volatile solvent extraction
Application: Preparation of natural flower
producing the finest perfumes.
oils
Principle: based on the liposolubility of volatile
oils
Solvents:
Lipids of high degree of purity e.g.
 Fats (lard : tallow in a mixture 2:1)
 Fixed (olive oil)
Techniques:
 Enfleurage (hot & cold)
 Pneumatic method
 Maceration (in fixed oils)
Enfleurage Process- Preparation of jasmine oil
 Equipment:
Great number of glass plates closely arranged in wooden
frames (or chassis).
 Procedure:
1.
2.
3.
4.
5.
6.
Spread the mixture of fat (lard / tallow 2: 1) on both surfaces
of each glass plate.
Cover the top of each plate with flowers or petals, so that
each layer of flowers is enclosed between 2 layers of fat.
Replace old flowers by fresh ones every 2-3 days
Repeat the process until the fat is saturated with the oil
Remove the last charge of flowers from the fat
("Defleurage")
Scrap & collect the fat layers, warm, filter through gauze &
cool  “Enfleurage product” or “Floral pomade”
Enfleurage Process
Flower Petals
Add
fat
mixture
[Lard & tallow (2 : 1)]
1) Enfleurage Product (floral pomade)
[Fat saturated with oil]
* Add absolute alcohol
* Triple extraction
* Cooling (remove most of fat)
2) Triple extract
[alc. solution of vol. oil + pigments + traces of fats]
Evaporation of alcohol
or fractional distillation
3)Absolute of Enfleurage
[Semi-solid, alcohol-free product]
Dilution with
H2O + NaCl
4)Volatile oil
Jasmine flowers
“Enfleurage” Process
Cold Enfleurage
Hot Enfleurage
Super critical fluid extraction
Principle: based on using liquefied gases e.g. CO2
under specific temperatures & pressures as
extracting solvents. Under these conditions these
gases are liquids but maintain the penetrating
properties of gases & allow more efficient
extraction. The oils obtained are of closest
composition to the natural oils.
Process
Distillation
Applications
For
dried
&
Advantages
fresh Cheapest
Disadvantages
method High temperature
material, rich in volatile (apparatus, solvent & presence of water
oils with thermostable & source of heat)
may
constituents
constituents.
Scarification
For preparation of oils -Carried
& Expression
present
in
at
room Expensive
large temperature
need
amounts in outer peels
oils
Suitable for
-Carried at room or Expensive
low temperature
sensitive oils present in
small amounts
to
high
with
more natural odors.
material with heat-
due
of
sensitive constituents.
fresh
the
number of workers
of fruits & rich in heat- -Yields
Extraction
affect
oils
number
with workers.
more natural odors
to
use of solvent & / or
high
-Yields
due
of
Methods based on enzymatic hydrolysis
of glycosides
Glycosides with volatile aglycones are found in:
1. Volatile oil-containing plants e.g. mint,
rosemary, Pinus spp., cinnamon & celery.
2. Plants devoid of volatile oils e.g. Gaultheria
spp., black mustard & bitter almond.
Black mustard
The volatile aglycones are known as the
"essential oils" of the plants e.g.
1. Methyl salycilate = oil of wintergreen
2. Allyl isothiocyanate = volatile oil of
black mustard
3. Benzaldehyde = volatile oil of bitter
almond
Bitter almond
Gaultheria sp.
Methods based on enzymatic hydrolysis
of glycosides: Principle
1. Plant material + enzymatic hydrolysis 
volatile aglycones in the hydrolysate
2. Hydrolysate + distillation or extraction with
organic solvent  volatile aglycone
Fixed oil if present in large amount in the plant material
should be removed by expression before hydrolysis
Examples of glycosides with volatile aglycones
Plant name
Gaultheria
procumbens
(Ericaceae) &
Betula lenta
Non-volatile
Glycoside
Volatile
aglycone
Other hydrolytic
products
Hydrolytic
enzyme
Gaultherin
Methyl salicylate
Primeverose
(Xylose + Glucose)
Gaultherase
Monotropin
Methyl salicylate
Glucose
Gein
Eugenol
Glucose
-Glucosidase
Sinigrin
Allyl isothiocyanate
Glucose + Potassium
acid sulfate
Myrosin
Glucovanillin
Vanillin
Glucose
-Glucosidase
Amygdalin
Benzaldelhyde
Gentiobiose
(2
glucose units) + HCN
Amygdalase &
Emulsin
(Betulaceae)
Geum urbanum
(Rosaceae)
Brassica nigra
(Brassicaceae)
Vanilla planifolia
(Orchidaceae)
Amygdala amara
(Prunus
amygdalus,
Rosaceae)
Preparation & purification of volatile oil
of bitter almond
1.
2.
3.


Seeds crushed & fixed oil removed by expression
Cake macerated in water for few hours, at 40ºC in a closed vessel
Amygdalin  hydrolysis (Amygdalase + Emulsin)  Benzaldelhyde
+ 2 glucose + HCN
Steam distillation  benzaldehyde + HCN (free state or as
benzaldehyde cyanohydrin)
Purification of bitter almond oil or "Removal or fixation of HCN"
By transformation to the non-volatile Ca2Fe(CN) 6 : Impure
distilled oil + Ca (OH)2 +FeSO4+ redistillation
Detection of residual HCN in the purified oil
Prussian blue test: Oil + NaOH (t.s.) & shake, if any traces of HCN
 NaCN + FeSO4 (traces of Fe+++ ions) + HCl & warm  Fe4 Fe
(CN)6]3 (ferric ferro cyanide), bluish black in color.
2 HCN + Ca (OH) 2
Volatile
3 Ca (CN) 2 + FeSO4
Ca (CN)2 + 2H2O
Non-volatile
Ca2 Fe (CN)6 + CaSO4
Non-volatile
Determination of
percentage of volatile oil
in plant material
Miscibility with alcohol
1. Most volatile oils are miscible
with absolute alcohol.
2. Oils highly miscible with
alcohol of low concentrations
are usually rich in oxygenated
constituents.
3. Decreased miscibility with
alcohol of low concentrations
 adulteration with non-polar
solvents e.g. petroleum ether
(turbidity) or fixed oils
% v/w = Vol of oil × 100 / Wt of drug
Physical Examination: helps in evaluation of the oil sample &
detection of adulterants
Odor
Detection of any abnormal odor (by smelling 1
or 2 drops of the oil applied on a filter
paper)  adulteration or deterioration
during storage
e.g. orange oil acquires a caraway odor on bad
storage due to autoxidation of limonene
to carvone & carveol
Solubility
1.
Oils are soluble in non-polar solvents as
benzene, carbon disulfide & light
petroleum.
2.
Any turbidity  moisture
Specific gravity
Apparatus: pycnometer (specific gravity
bottle)
Sp. gr. gives an indication on composition
1.
Oils with sp. gr. < 0.9, rich in
hydrocarbons & aliphatic compounds
2.
Oils with sp. gr. > 1.0, rich in aromatic &
S compounds.
3.
Oils with 0.9 > sp. gr. < 1.0, contain
different types of constituents
Optical rotation [Apparatus: Polarimeter ]
1.
Determination helps in detection of
adulteration & identification of the
variety of the sample e.g.

French oil of turpentine is levorotatory [l
(-)] as it contains l-pinene in high
concentration.

American
oil
of
turpentine
is
dextroratory [d (+)] as its major
constituent is d-pinene.
2.
Gives indication on the method of
preparation of the volatile oil isolate:

All synthetic compounds are racemic
(dl).

Natural compounds are generally
optically active present in (l) or (d)
forms.
Example: natural camphor is (l) or (d) while
synthetic camphor is (dl).
Refractive index [Apparatus: Refractometer]
Refractive Indices of volatile oils range from
1.4- 1.6 any deviation  adulteration
Pycnometer
Polarimeter
Abbe refractometer
Chemistry of volatile oils constituents
Types of constituents detected in volatile oils:
V. O. are complex mixtures formed of:
1.
Terpenoids (mainly mono- & sesquiterpenoids)
2.
Phenyl propanoids (C6-C3, aromatic)
3.
Aliphatic compounds (acyclic, straight chain compounds
which may be terpenoids).
4.
Miscellaneous compounds
organo-sulfur compounds.
e.g.
organo-nitrogen
&
 Each group includes non-oxygenated (hydrocarbons) &
oxygenated compounds.
 Oxygenated constituents are generally responsible for
the characteristic odor of the oil.
Removal of terpenoid hydrocarbons

Oils rich in terpenoid hydrocarbons deteriorate rapidly on
storage due to oxidation & polymerization  bad smelling
(with turpentine-like odor) & resinified products.

Removal of most terpenoid hydrocarbons  "terpenelessoils" by any of the following methods:
1.
Fractional
distillation
under
reduced
pressure:
hydrocarbons have lower b.p. than oxygenated
compounds, they distill first & are rejected.
2.
Column chromatography on silica gel: hydrocarbons are
eluted with n-hexane then oxygenated compounds with
absolute alcohol.
3.
Selective extraction oxygenated components with dilute
alcohol followed by distillation.
“Terpeneless oils”
Oils from which most terpene
hydrocarbons are removed
1.
More expensive than natural
oils
2.
Richer
in
compounds.
3.
More soluble in low-strength
alcohols.
4.
Used in smaller amounts to
give the same strength of
odor.
5.
oxygenated
More stable being less liable
to deterioration
“Volatile oil isolates”
 An isolate is a single
chemical substance
isolated from the oil
“Oleoptene & Stearoptene”
1. Stearoptene = solid fraction
separating on cooling a v.o.
(previously
known
as
camphors), consists of 1 or
more
solid
(mainly
oxygenated ) compounds
2. Oleoptene
=
remaining
liquid
fraction,
mainly
formed of hydrocarbons
Isolation of volatile oil constituents

Physical methods (cooling, fractional distillation,
fractional crystallization & preparative gas
chromatography)

Chemical methods depend on:
1. Solubility differences in acids or alkalis
2. Derivatization (due to presence of functional
groups).
3. Adduct
formation
compounds).
(specific
for
certain
Chemical methods for isolation of V.O. constituents
Solubility in alkalis:
1. Compounds containing -COOH group (strongly acidic) + mild alkali
(Na2CO3)  water soluble Na salts (decomposed by acids).
2. Phenolic compounds (mild acids) + aqueous NaOH or KOH (strong alkalis)
 water soluble Na or K phenates (decomposed by acids)  phenol.
Derivatization:
1. Alcohols  esterification  phenyl urethans or acid phthalates
2. Carbonyl compounds  derivatives e.g. crystalline
semicarbazones, phenyl hydrazones & oximes.
bisulfites,
Formation of crystalline additive products
1. Geraniol, benzyl & cinnamyl alcohols + anhydrous CaCl2.
2. Carvone + H2S gas in presence of NH3.
3. Cineole + strong acids (e.g. H3PO4) & resorcinol
4. Unsaturated terpene hydrocarbons + HCl, HBr & NOCl (nitrosyl chloride
or Tilden’s reagent).
5. Azulenes +
 Strong mineral acids e.g. H3PO4 and H2SO4
 Ferrocyannic acid
 Nitrocompounds e.g. picric, styphnic & tortylic acids.
Terpenoids (Terpenes)
 They constitute the largest known group of secondary
metabolites.
 The term “terpenes” should better be used to indicate the
unsaturated hydrocarbons
 All yield isoprene as final product of destructive distillation
(= pyrolysis).
 Isoprene, a 5 carbon-atom unit, is the building unit of all
terpenoids
1 CH
2
4
H2C
3
C
h
t
C 2
Abbreviated structure
h=head, t=tail
CH3
Isoprene, 2-methyl 1:3 butadiene, 1,3 isopentene
Isoprene rule for formation of terpenoids
 Theoretical biogenetic rule which states that: “Each group
of terpenes originates from the head-to-tail condensation of
a variable number of isoprene units”.
Isoprene
Isoprene
Isoprene
Isoprene
Monocyclic
Acyclic
monoterpene monoterpene
Bicyclic
Monoterpene
Isoprene
Acyclic sesquiterpene Monocyclic sesquiterpene
Coupling of isoprene units to yield mono- & sesquiterpenoids
Terpenoids in Essential Oils
 Thousands are identified in essential oils
 Mainly mono- or sesquiterpenoids (volatile & of low
molecular weight)
 Acyclic (i.e. aliphatic) or Alicyclic (i.e. with nonaromatic ring-structures)
 Hydrocarbons or oxygenated (alcohols, aldehydes,
ketones, esters, ethers, oxides or peroxides)
 Often optically active occurring as d-, l- & dl isomers
Monoterpenoids (C 10)
1. Most abundant class of essential oil constituents.
2. Consist of 2 molecules of isoprene
3. Hydrocarbons have the empirical formula C10H16
4. Acyclic or alicyclic (mainly mono- & bicyclic)
Terpenoids in Essential Oils
Sesquiterpenoids (C15)
1.
Present in the high boiling point fractions of the oils (250-280oC).
2.
Mostly viscous liquids or may be crystalline.
3.
Consist of 3 molecules of isoprene
4.
Hydrocarbons have the empirical formula C15H24
5.
Acyclic, monocyclic or polycyclic.
6.
Occur in more than 100 different skeletons with ring size
ranging from 4, 7, 8, 10 & 11 C atoms.
Azulenes (C15H18)
1.
Usually discussed under sesquiterpenoids because they have
the same number of C atoms & distill in the same boiling range.
2.
But, they possess aromatic properties due to high conjugation &
are highly colored (generally blue, green or violet) e.g.
Chamazulene in oil of chamomile.
Nomenclature of terpenoids

Chemical names are derived from the corresponding saturated
hydrocarbon skeleton
1.
2.

The acyclic monoterpenoids are 2, 6-dimethyl octane (myrcane)
derivatives.
Most monocyclic monoterpenoids are para-menthane rarely metamenthane derivatives.
3.
Bicyclic monoterpenoids are thujane, carane, pinane, camphane or
fenchane derivatives.
4.
Acyclic sesquiterpenoids are trimethyldodecane derivatives.
5.
Mono- & polycyclic sesquiterpenoids are bisabolane, humulane,
elemane, germacrane cadinane, santalane, cedrane derivatives
etc…
6.
The number & position of the double bonds are indicated e.g. a
double bond between C1 & C2 by 1 ; while a double bond between
C1 & C6 by 1(6)
Trivial names are better adopted for facility.
Saturated hydrocarbon skeletons of
mono- & sesquiterpenoids
MONOTERPENOIDS
SESQUITERPENOIDS
Myrcane
p-Menthane
m-Menthane
Trimethyldodecane
Thujane
Carane
Elemane
Pinane
Germacrane
Bornane (Camphane) Fenchane
Bisabolane
iso-Camphane
Humulane
Cadinane
Isomerism of Monoterpenoids
 Structural isomerism due to
shift in the double bonds,
e.g.
Myrcene
Ocimene
Limonene
Terpinene
 Structural isomerism due to
shift in the position of a
substituent group e.g. pmenthadiene
&
mmenthadiene derivatives.
Limonene
Sylvestrene
Isomerism of Monoterpenoids
 Geometrical isomerism: e.g. the cis-trans isomeric alcohols, nerol &
geraniol.
CH 2OH
H
Geraniol
H
CH 2OH
Nerol
 Optical isomerism: due to the presence of one or more asymmetric C
atoms e.g. dipentene occurs in d, l & dl forms due to asymmetry at C4
(not involved in a double bond), while terpinene is optically inactive.
 Strainless ring isomerism: chair & boat configurations more stable
than planar configuration.
 Isomerism
due to molecular rearrangement of the ring
structures: e.g. from pinane to camphane etc….
Phenyl propanoids (C6-C3) or
Aromatic constituents
 Less common than terpenoids.
 Contain a C6 phenyl ring to which is attached a C3
propane side chain
 Many are phenols (e.g. eugenol), phenol ethers (e.g.,
anethole, safrole,
cinnamaldehyde).
apiole)
or
aldehydes
(e.g.,
 The propane side chain may be formed of 2 C (C6-C2)
or 1 C (C6-C1) e.g. vanillin, methyl salicylate &
methyl anthranilate.
 Certain aromatic C10 compounds e.g. p-cymene,
thymol &
carvacrol can be described under
monoterpenoids.
Examples of phenyl propanoids in volatile oils
OH
OH
p-Cymene
OCH3
OH
Thymol
Carvacrol
O
OCH3
O
O H CO
3
O
OCH 3
Anethole
Eugenol
Saffrole
OH
OCH3
Apiole
O
CHO
OCH 3
CHO
Vanillin
CH2 OH
OH
Cinnamaldehyde
Methyl salycilate
Phenyl ethyl alcohol