Geranyl acetate, Geranyl formate, Geranyl butyrate, Linalyl acetate, Methyl Salicylate, Methyl cinnamate, Ethyl cinnamate, Methyl anthranilate, Benzyl acetate, Benzyl benzoate,1,8-cineole Eucalyptol, Cajuputol and Ascaridole

1. Phytochemistry
Volatile oils
Esters, oxides & peroxides
By
Dr. Mostafa Mahmoud Hegazy ( PH.D.)

2. •Many volatile oils owe their aroma to the presence
of esters.
•The most common esters are the acetates of
terpineol, borneol and geraniol.
•Aging of perfumes is generally carried to allow
esterification to take place and thus improving the
fragrance.
Esters

3. Esters isolated from volatile oils could be classified
according to the acyl radical into:
•Esters of aliphatic acid; formic, acetic and
butyric
•Esters of aromatic acid; benzoic, salicylic and
cinnamic
•Nitrogen-containing esters; methyl anthranilate
Classification

4. H
CH2OCOCH3
H
CH2OCOCH3
OCOCH3
CH3
C
O
O
CH2
C
O
O
H2
C
C
OH
O
O CH3
C
NH2
O
O CH3
OHO
O
H2
C
OCOCH3
Geranyl acetate Linalyl acetate Menthyl acetate
Benzyl acetate Methyl salicylate Benzyl benzoate
Benzyl salicylate Methyl anthranilate
Examples of esters detected in volatile oils

5. Identification of esters
1. By saponification followed by identification
of both alcohols and acids resulting from
hydrolysis.
2. By aminolysis,(i.e. hydrolysis using amines) is valuable
as a method of identification of the acyl group (acid radical)
the ester is refluxed with benzyl amine to gives N-substituted
benzyl amine.
RCOOR' + NaOH RCOONa + R'OH
Ester Sodium salt Alcohol
RCOOR' + C6H5.CH2.NH2
Ester
RCONH.CH2.C6H5 + R'OH
N-substituted benzylamide AlcoholBenzylamine

6. Determination of esters
Based on hydrolyzing the esters by alc. KOH
and determination of ester value
• Saponification of the esters using a known
excess of standard alcoholic alkali (KOH).
• Determination of the amount of alkali
consumed for ester(s) hydrolysis after back
titration of the excess non-reacting alkali
with standardized acid.
• Calculation of the ester percentage.

7. Isolation of esters
• Esters are difficult to isolate in pure
form because;
1. Boiling range of many esters is so close,
they cannot be separated by fractional
distillation.
2. Many esters are unstable; may be
undergo hydrolysis during distillation.
3. They do not form crystalline derivatives
because they lack special function
groups, except methyl anthranilate.

8. Esters of aliphatic acid
Esters of Geraniol
1. Geranyl acetate
• Oil of Citronella, Lemon grass
• and Lavender.
• Rose-like odor
• Isolation by fractional distillation in vacuum
Identification
By hydrolysis → Geraniol + acetic acid.
Widely used in perfume, cosmetic
and soap industries to imitate rose oil.
2. Geranyl formate
• Oil of Geranium.
• Rose-like odor
3. Geranyl butyrate
• Oil of Boronium pinnata (Rutaceae)
• Rose-like odor
H
CH2OCOCH3
Geranyl acetate
Terpinolene form
H
CH2OCOCH3
Geranyl acetate
Limonene form

9. Esters of Linalol
• Linalyl acetate
• Source
• Oils of Lavander, Bergamot and Jasmin
• a pleasant lavender-like odor
• It can be obtained by fractional distillation under high
vacuum, since it is easily decomposed on steam
distillation.
OCOCH3
Linalyl acetate

10. Esters of aromatic acid
1.Methyl Salicylate
Occurrence: 99% of the oil of wintergreen Gaultheria
procumbens after hydrolysis of gaultherin glycoside.
Identification: It gives red-violet color with FeCl3
Uses: Local irritant, antiseptic and antirheumatic.
OCH3
O
O-glu-xyl
OCH3
O
OH
H2O+
Gaultherin Methyl salicylate
Gaultherase
+ glucose Xylose+

11. 
Action of alkalis:
- In dilute aqueous alkalis e.g. KOH, it readily dissolves yielding K methyl salicylate
(the phenolic OH group gives the phenate).
- In more concentrated aqueous solutions, e.g. 3% NaOH, it is sparingly soluble due
to the formation of sodium methyl salicylate which precipitates (Na phenates are less
soluble than the K salts).
- When heated with excess alcoholic alkalis (KOH or NaOH), both ester and
phenolic groups are involved in the reaction (saponification and formation of
phenate) and on acidification salicylic acid is obtained.
C
OH
O
O CH3
Methyl salicylate
C
OK
O
O CH3
Potassium methyl salicylate
C
OK
O
OK
C
ONa
O
O CH3
Sodium methyl salicylate
Dil.KOH 3% NaOH
Alc.KOH
C
OH
O
OH
[H+
]
Salicylic acid

12. Toxicity:
-Ingestion of relatively small amounts of methyl salicylate may
cause severe poisoning and death (average lethal dose 10 ml
in children and 30 ml in adults).
-Symptoms of toxicity are nausea, vomiting, acidosis,
pulmonary edema, pneumonia, convulsions and death.
OHO
O
H2
C
Benzyl salicylate
Benzyl salycilate
Benzyl salycilate is used as fixative in perfumes and
as ingredient in sunscreen preparations.
OC
Menthyl salicylate
HO
O
Menthyl salycilate
It is almost odorless.
It is used as ingredient in sunscreen preparations.

13. • 2- Cinnamic acid esters
• These are used in perfume industry and
• as flavoring agents in foods and cosmetics.
• Methyl cinnamate that imparts a strawberry-like odor.
• Ethyl cinnamate that imparts a cinnamon-like odor.
CH=CHCOOCH3

14. Esters containing nitrogen
These are organo-nitrogen compounds containing an ester group. The most
common are derivatives of anthranilic acid or o-aminobenzoic acid.
3. Methyl anthranilate
Oils of Jasmin and Neroli
It has a beautiful violet fluorescence that is apparent in any volatile oil
containing it.
• Isolation
• It can be readily isolated by:
• Shaking the oil with dilute H2SO4 (due to basic amino group).
• Cooling to crystallize the sulfate formed.
• Purification by recrystallization of the sulfate from alcohol.
• Regeneration of the ester by treatment with NaOH.
• Identification
1- By preparation of derivatives of the amino group e.g. picrate, benzoate etc…
2- By physical examination of the characteristic violet fluorescence.
• Cinnamyl anthranilate is a synthetic compound, that is largely
used in food, soap and perfume industries as flavoring agent to give a
grape or cherry-like odor.
C
NH2
O
O CH3
Methyl anthranilate

15. 4. Benzyl acetate
• Source: It is a constituent of Jasmine oil.
• Uses
• It is used in perfumery and as solvent for cellulose acetate.
• If ingested, it causes GI irritation with vomiting and diarrhea.
• It is also irritating to skin, eyes and respiratory tract.
5. Benzyl benzoate
• Balsam Peru, Balsam Tolu
• Separated by cooling
• Uses
• Although it may cause eye and skin irritation,
• benzyl benzoate has a wide variety of uses as:
• Scabicide and pediculicide.
• Solvent for cellulose acetate, nitrocellulose and artificial musk.
• Substitute for camphor in celluloid and plastic pyroxylin compounds.
• Perfume fixative.
Flavoring agent in confectionery and chewing gum
CH3
C
O
O
CH2
Benzyl acetate
C
O
O
H2
C
Benzyl benzoate

16. Oxides
These are internal ethers, the most widely distributed is the monoterpenoid
cineole, and other examples are the sesquiterpenoids bisabolol oxides.
O
O O
1,8-Cineole
O
H
OH
H
O
OH
H
(-)α-Bisabolol oxide A (-)α-Bisabolol oxide B
Examples of oxides in volatile oils
Monoterpenoids
Sesquiterpenoids

17. Monoterpene oxides1,8-cineole
Eucalyptol, Cajuputol
•It is widely spread in essential oils, next constituent after α-pinene in
frequency.
•Major constituent of oils obtained from certain Eucalyptus species (30 - 70 %),
oil of Cajuput
• (Melaleuca leucadendron, Myrtaceae) (40 %), and oil of Laurel leaf (50 %).
O
O
O
1,8-Cineole

18. Isolation •It can be isolated by one of the following methods, based on its amount in the
oils:
• Fractional distillation followed by cooling the fraction collected at 170-180 º C,
crystalline cineole is collected.
• Formation of additive products with:
• Halogen acids HCl or HBr to yield the crystalline C10H18O. HCl or C10H18O. HBr.
• Phenols e.g. 50% resorcinol.
• Syrupy phosphoric acid, which is decomposed by hot water (regeneration).
This reaction is also used for estimation in case of oils rich in the constituent.
O
Cineole Phosphoric acid complex
O
2 OH
OH
Cineole resorcinol complex
. . H3PO4
OH O
OH
Dehydration
1,8-CineoleTerpin hydrate
Synthesis
It can be obtained by dehydration of terpin
hydrate.

19. Properties
• Colorless syrupy oil, b.p. 176 - 177 º C with camphor-like odor and a pungent
taste.
• It is a terpenoid inner ether, quite stable and can be distilled over metallic Na
without undergoing any change and is not attacked by the normal reducing
agents.
• It readily forms additive compounds (with HBr, HCl, phenols and H3PO4).
• Determination
• Several methods are proposed including:
• 1- The congealing point method ( Kleber's and Von Rechenberg's method )
• The congealing point of the cineole-containing oil is determined, and cineole
content is read from specific tables. A disadvantage of the method is that the
whole process should be carried at low temperatures (below zero degree).
• 2- The o-cresol method (Cocking's method)
• This depends on that the freezing point of a mixture of cineole and o-cresol
is lowered due to the amount of other constituents in the assayed oil. The
percentage w/w of cineole corresponding to the freezing point is then
calculated from special tables.

20. • 3- The phosphoric acid method (Scammel's method , modified
by Baker and Smith )
• This depends on that cineole forms with syrupy phosphoric
acid (sp.gr. 1.75), on the cold, a loose additive compound from
which it is regenerated by the addition of warm water.
• The volume of cineole liberated is measured in the graduated
neck of a Cassia flask and its percentage in the oil calculated.
• This method is used for large amounts of cineole (not less than
50 %).
• 4- Other colorimetric methods have been devised and are
useful in case of low cineole- containing oils.

21. Identification & Uses
Identified by:
– Microchemical tests:
+ 5% hydroquinone → colorless prisms
+ 50% soln of resorcinol → leaf-like crystals
Uses
– Internally: expectorant in chronic bronchitis
– Locally: mild anesthetic and antiseptic in
inflammations

22. Monoterpene peroxides
Ascaridole
In oil of chenopodium
• The only naturally occurring monoterpenoid peroxide
• Decomposes with explosion by heat and acids
• Used as: Anthelmintic against round worms
O
O
O
O O
O
Ascaridole

23. • Isolation
•
• It is obtained by repeated fractional distillation of the oil
in vacuum and collecting the fraction boiling at 95 - 98
ºC (avoid raising the temperature to prevent explosion).
•
• Properties
• Viscid yellow oily liquid, with disagreeable odor and flavor.
• Insoluble in water but soluble in dilute acetic acid.
• It can not be distilled at atmospheric pressure.
• It explodes with violence if :
• heated to 130 -135º C ( decomposition ).
• treated with H2SO4 , HCl , HNO3 or H3PO4 .
• It liberates iodine from KI in acetic acid solution (used for
determination).
•

24. Identification
It does not form any crystalline derivatives and could be
identified through:
1- Treatment with ferrous sulfate to yield ascaridole glycol,
which is, characterized by formation of its monobenzoate or
dibenzoate esters with specific melting points.
2- Reduction with hydrogen / Pd to give cis 1,4 terpin (m.p. 116
-117 º C).
O
O
O
O
OH
OH
Ascaridole Ascaridole glycol
FeSO4
[O]
O
O
OH
OH
Ascaridole cis 1,4 Terpin
H2/Pd

25. • Determination
• Based on its oxidizing character on KI in
strong acidic medium (HCl+acetic acid),
the liberated iodine is titrated against st.
sod. Thiosulphate.
• The reagents are cooled before mixing
with the oil to;
1. Avoid explosion (exothermic reaction)
2. Avoid volatilization of iodine by heat of
the reaction
3. Avoid part of liberated iodine entering in
2 ry reactions (addition reaction to double
bonds)

26. Composition of some important
volatile oils
Major
constituents
Name of oil Botanical origin Isolates
Oxides &
Peroxides
Eucalyptus oil Eucalyptus globulus Cineole (over 70%) ,
terpenes etc …
Cajuput oil Melaleuca spp. Cineole (50-60 %)
terpenes alcohols &
esters.
Chamomile oil Matricaria chamomilla Bisabolol, bisabolol
oxides (50%) &
Chamazulene
(2-10 %).
Chenopodium oil Chenopodium
ambroisoides var.
anthelmintica
Ascaridole (60 - 75 %).

27. For more educational lectures
cognosy4all.blogspot.com

28. cognosy4all.blogspot.com
Pharmacognosy and Herbal Medicine Dr. Mostafa