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
alkaloid after Pelletier

e.g.

Pelletierine

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
[analgesics,
laxatives,
etc..]

activity
cardiotonics

B. Biosynthetic
origin,
solubility
properties & key functional groups
C. Chemistry
properties

&

common

physical

B.According to biosynthetic origin,

solubility properties & key functional
groups:

1.

Phenolics: e.g. flavonoids & their glycosides,

phenyl propanoids, anthocyanins, xanthones,
tannins & quinones
2. Terpenoids: e.g. carotenoids, steroids & the
major constituents of volatile oils
3. Organic acids & lipids: e.g. simple organic
acids (citric, oxalic & ascorbic), fatty acids (in
the form of esters in fixed oils, fats & waxes)
4. Nitrogenous compounds: e.g. alkaloids &
cyanogenic glycosides
5.
Water-soluble carbohydrates & their
derivatives: e.g. monosaccharides,
oligosaccharides & water-soluble glycosides
6.
Macromolecules: e.g. proteins &
polysaccharides

C.According to chemistry & common

physical properties
This classification will be adopted for
convenience, the major groups are:
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 = etherlike 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

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
Musk, musk-like
products (civet,
castoreum) &
ambergris
Secretions
produced for
attraction or
protection

:Botanical sources
Mainly in higher
plants
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 cells:
(Lauraceae & Zingiberaceae)
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
cross-pollination (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.

2.

Spices & condiments: in food seasoning (to impart

aroma & flavor) or as preservatives

3.

4.

Therapeutic & medicinal uses: local stimulants,

carminatives, diuretics, mild antiseptics, local
irritants, anthelmintics, parasiticides

Flavoring agents: in food (e.g. beverages, soups,

bakery products, confectionery) & pharmaceutical
industries

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 150-

300C. In order to reduce decomposition, volatile

oils are distilled in the presence of water.

The mixture will boil below 100C [Daltons 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
H2 O
Distillation

Steam 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.
containing moisture)

Commercial
preparations

Oils of turpentine &

rose

Oils of clove,
cinnamon &
citronella

Oil of peppermint

Mode of
charging

Plant material
dipped in H2O

-H2O present but not

in contact with the
plant.
-Steam is generated
in the still &
penetrates the drug
-Dried material is
moistened before
charging

Steam
pressure

-H2O is absent.
-Steam is introduced by
pipes & forced through
the plant material
placed on perforated
trays

atmospheric

Can be modified

100C

Can be modified

Temperature
Rate & yield

Relatively low

Advantages

-Least expensive

Better

The best
Hydrolysis is

Method suitable for oils

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)

Purification
(Rectification) of
distilled oils

Florentine
Receivers

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--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 methodsApplication

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

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
corresponding concrete.

Preparation:

repeated
absolute alcohol

than

extraction

the
with

Impurities: removed by strong cooling &

filtration

Non-volatile solvent extraction

Application: Preparation of natural flower

oils producing the finest perfumes.

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
wooden
frames (or chassis).

closely

arranged

in

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

Applications

Advantages

Distillation For dried & fresh Cheapest

material,

rich

Disadvantages
High

in method

temperature

volatile oils with

(apparatus,

&

presence

of

thermostable

solvent & source water may affect

constituents

of heat)

the constituents.

Scarificatio

For preparation of

-Carried at room

Expensive due to

n&

oils present in large

temperature

need of high

Expression

amounts

in

peels

fruits

of

rich

in

outer

number of

&

-Yields oils with

heat-

more natural

sensitive

workers

odors.

constituents.
Extraction Suitable

for

fresh material

with

heat-sensitive oils

-Carried at room

Expensive due to

or low

use of solvent & /

temperature

present in small
amounts

or high number
of workers.

-Yields oils with

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
Black mustard
almond.
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
Bitter almond
3. Benzaldehyde = volatile oil of
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) &

Non-volatile
Glycoside

Volatile
aglycone

Other hydrolytic
products

Hydrolytic
enzyme

Gaultherin

Methyl
salicylate

Primeverose
(Xylose + Glucose)

Gaultherase

Monotropin

Glucose
Methyl
salicylate

Betula lenta
(Betulaceae)
Gein

Eugenol

Glucose

-Glucosidase

Brassica nigra
(Brassicaceae)

Sinigrin

Allyl
isothiocyanate

Glucose +
Potassium acid
sulfate

Myrosin

Vanilla
planifolia
(Orchidaceae)

Glucovanillin

Vanillin

Glucose

-Glucosidase

Amygdalin

Benzaldelhyde

Gentiobiose
(2 glucose units) +
HCN

Amygdalase &
Emulsin

Geum
urbanum
(Rosaceae)

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 40C 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
miscible with
alcohol.

oils are
absolute

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% v/w = Vol of oil 100 / Wt of

drug
polar
solvents
e.g.
petroleum
ether

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 lpinene 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

compounds which may be terpenoids).

4.

Miscellaneous compounds e.g. organo-nitrogen

& organo-sulfur compounds.

chain

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

"terpeneless-oils" 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
terpene

which

most

hydrocarbons are removed

1.

More
expensive
natural oils

2.

Richer
in
compounds.

than

oxygenated

3.

More
soluble
in
strength alcohols.

4.

Used in smaller amounts

to give the same strength
of odor.

5.

low-

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
functional groups).

to

presence

of

3. Adduct formation (specific for certain

compounds).

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 bisulfites,
semicarbazones, phenyl hydrazones & oximes.

Formation of crystalline additive products

1.Geraniol, benzyl & cinnamyl alcohols + anhydrous CaCl2.
2.Carvone + H2S gas in presence of NH 3.
3.Cineole + strong acids (e.g. H3PO4) & resorcinol
4.Unsaturated terpene hydrocarbons + HCl, HBr & NOCl (nitrosyl
chloride or Tildens 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
CH3

Abbreviated structure
h=head, t=tail

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- &

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 (250280oC).

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.

The acyclic monoterpenoids

(myrcane) derivatives.

are

2.

Most monocyclic monoterpenoids are para-menthane rarely

meta-menthane derivatives.

3.

Bicyclic monoterpenoids are thujane,

camphane or fenchane derivatives.

4.

Acyclic
sesquiterpenoids
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)

are

2,

6-dimethyl

carane,

octane

pinane,

trimethyldodecane

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.
p-menthadiene
&
mmenthadiene
derivatives.

Limonene

Sylvestrene

Isomerism of Monoterpenoids
Geometrical

isomerism: e.g. the cis-trans isomeric alcohols,

nerol & geraniol.

CH2OH
H

Geraniol

Optical

H
CH2OH
Nerol

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, apiole) or
aldehydes (e.g., cinnamaldehyde).

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. pcymene, thymol &

carvacrol
described under monoterpenoids.

can

be

Examples of phenyl propanoids in

volatile oils
OH

OH

p-Cymene
OCH3
OH

Thymol

Carvacrol
O

OCH3

O
O H CO
3

OCH3

Anethole

Eugenol

Saffrole

OH
OCH3

Apiole
O

CHO
OCH3

CH2OH

OH

CHO
Vanillin Cinnamaldehyde Methyl salycilate

Phenyl ethyl alcohol