Phytochemistry 1 (PHG 2024)
Volatile oils (Oxygenated terpenes)
Lecture 5
By the end of this lecture you
will be able to:
• Understand the chemistry of volatile oils
constituents ( oxygenated terpenes).
• Compare between different chemical classes
of oxygenated terpene hydrocarrbons.
• Enumerate & describe some example
compounds belong to different classes of
oxygenated terpene hydrocarbons.
C- Oxygenated terpenes: Acyclic terpenoids alcohol
Acyclic monoterpenoids
HO
H CH2OH
CH2OH CH2OH H
-Citronellol -nerol - Geraniol (+)-Linalol
Acyclic sesquiterpenoids
OH
CH2OH
C-Oxygenated Terpenes
1- Acyclic monoterpene alcohol (1ry):
Citronellol
Source: d-form is mainly obtained from oil of lemon grass (50 %), l-form
from oil of geranium (35 - 40 %) and oil of rose (40 – 50 %).
Properties: Citronellol is optically active colerless liquid, that can be easily
oxidized to citronellal.
Preparation: By fractional distillation (225-226 oC).
Uses:1- Citronellol is used in perfume industry,
cosmetic and soap industries to impart a rose-like odor.
2- Potent insect repellant.
C-Oxygenated Terpenes
1- Acyclic monoterpene alcohol (1ry):
Geraniol & Nerol
Source: Geraniol is present in oils of geranium and rose (50 %), lemon grass
(40 %).
➢Nerol isobtained from oils of neroli (bitter orange), bergamot.
Preparation: Both nerol and geraniol are colorless, optically inactive (c.f.
citronellol) liquids with rose-like odor (similar to citronellol). They can be
easily oxidized to citral a & b.
Due to the higher degree of unsaturation they are more reactive and
consequently more susceptible to degradation.
Uses:1- Both nerol and geraniol are used in perfume industry, cosmetic and
soap industries to impart a rose-like odor.
2- Geraniol is potent insect repellant (similar to citronellol).
C-Oxygenated Terpenes
Isolation: Geraniol is isolated through formation of a crystalline adduct
with calcium chloride as follows:
-Addition of anhydrous CaCl 2 to the oil containing geraniol.
-Washing of the deposited adduct with warm water [to decompose the
complex and regenerate geraniol].
➢ This method is used to separate geraniol from citronellol in oil of rose.
➢ Nerol is difficult to be obtained in a pure form (i.e highly reactive
compound).
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C-Oxygenated Terpenes
1- Acyclic monoterpene alcohol (3ry):
HO
*
Linalool
(
+ )
-Li
nal
ol
Source: d-form : coriander oil, l-form : oil of lavender.
•Properties: optically active liquid with a characteristic lavender-like
odor
•Highly unstable, due to the presence of two double bonds and a
tertiary alcoholic group.it is easily dehydrated to yield monoterpenoid
hydrocarbons (e.g. myrecene).
•
Uses: Linalool and its esters are used in perfume industry, cosmetic and
soap industries to impart a lavender-like odor.
C-Oxygenated Terpenes
2- Acyclic sesqueterpene alcohol:
OH
CH2OH
nerolidol Farnesol
Source: Source:
in oil of hops in oil of neroli
Tertiary alcohol Primary alcohol
C- Oxygenated terpenes: Cyclic terpenoids alcohol
Monoterpenoids Sesquiterpenoids
OH
H
OH OH OH
CH2OH
(-)-Menthol -Terpineol (-)-Borneol Carotol Santalol
Monocyclic Bicyclic Tricyclic
C-Oxygenated Terpenes
3- monocyclic monoterpenes alcohol (2ry):
H
1 *
Menthol H
4 *
3 OH OH
* H
M e n th o l ( - ) - M e n th o l
Source: The most common isomer is l-menthol .
Occurs in large amounts in oil of peppermint (Mentha piperita, Labiatae or
Lamiaceae) 60 - 65 %
Properties: optically active solid crystals with a characteristic peppermint-
like odor.
Isolation: It is obtained from peppermint oil by successive cooling and
collection of the deposited crystals.
Uses: 1-Local action: menthol is used as, counter irritant (rubefacient), mild
local anesthetic.
Systemic action: It exerts a and is used as carminative and antispasmodic,
improve symptoms of irritable bowel syndrome (IPS).
C-Oxygenated Terpenes
3- monocyclic monoterpenes alcohol (3ry):
OH OH
1
2
α-Terpeniol
* OH
8
T e r p e n io ls
Source: Camphor oil.
Properties: Optically active solid crystals.
Preparation: α- terpeniol can be easily prepared from limonene and α-
pinene by acid treatment.
Uses: In perfume industry. OH
or 6 0% H2S O 4
OH OH
L im o n en e − p in en e T erp in − T e rp e n io l
o r D ip en te n e
C-Oxygenated Terpenes
4- Bicyclic monoterpenes alcohol (2ry):
Borneol
Source: It occurs in many essential oils (e.g. Camphor oil).
Properties: Optically active solid crystals.
Preparation: Borneol can be easily prepared from α- pinene.
Uses: Bornyl isovalerate: sedative.
Bornyl - bromoisovalerate: sedative and hypnotic.
Cl OH
Cl
HCl gas Isomerization KOH
-10oC Molecular
Rearangement
Pinene Pinene hydrochloride Bornyl chloride Borneol
C-Oxygenated Terpenes
5- monocyclic sesquiterpenes alcohol (3ry):
H OH
α-bisabolol
(-) -B is a b o lo l
Source: It is a monocyclic tertiary alcohol that constitutes the major
component (about 50%) of the German chamomile volatile oil (Matricaria
chamomilla).
Uses: 1-bisabolol responsible of the ulcer-protective properties of
chamomile.
2-Promote wound healing.
6- Tricyclic sesquiterpenes alcohol (1ry):
α-santalol
−Sa
nta
lol CH
OH
2
Source: The main component in sandalwood oil.
Uses: Very efficient sedative (aromatherapy).
C- Oxygenated terpenes: Aldehydes in volatile oils
Acyclic Aldehydes
CHO CHO H H
CHO CHO H H CHO CHO
Citronellal Citral a or geranial Citral b or neral
Alicyclic Aldehydes
CHO CHO CHO
CHO
Safranal Myrtenal
Phellandral Perillaldehyde
Aromatic Aldehydes
CHO CHO CHO CHO CHO
OH
O CHO
Furfural
OCH3
Benzaldehyde Salicylaldehyde OCH3 OH
Cuminaldehyde Anisaldehyde Vanillin
C- Oxygenated terpenes: Aldehydes and ketones in volatile oils
Isolation and quantitative determination (For both aldehydes and ketons):
1- Reaction with sodium bisulfite:
They react with NaHSO3 to give crystalline bisulfite derivatives
(hydroxy sulfonic acid salts). On heating in presence of dilute acid or
Na2CO3 the carbonyl compound is regenerated. Stronger alkalis may
cause resinification of the product (aldol condensation).
OH OH -
C or C +
C O + NaHSO 3 SO 3 Na SO Na
d ilu te a c id o r 3
S o d iu m b is u lfite
N a2C O 3 / B is u lfite d e r iv a tiv e
2- Reaction with hydroxyl amine:
They react with hydroxylamine.HCl to yield oximes ppt. The original
aldehyde or ketone can be regenerated by acid treatment.
C O + H2N OH.HCl C N NH2 + H2O +HCl
xss Hydroxyl amine Oxime
Produced acid is tit. against alc.KOH
using MR in aldehyd and dimethyl yellow intenal
indicator in case of ketones
C-Oxygenated Terpenes
1- Acyclic monoterpenes aldehyde:
Citronellal
Source: Lemon grass oil (as citronellol).
Isolation: By fractional distillation or by formation of the crystalline
bisulfite from which the aldehyde is regenerated.
Preparation: Can be easily prepared from citronellol by oxidation.
Uses: In perfume industry.
Citral a and b
Source: Lemon grass oil
Properties: Its responsible for the taste and odor of lemon.
Citral a and b
Isolation: By formation of the crystalline bisulfite from which the
aldehyde is regenerated.
NOTE: Citral a can be separated from citral b. The crystalline sodium
bisulfite compound of citral a is sparingly soluble while that of citral b
is readily soluble in NaHCO3.
Separation of citronellal from citral:
Bisulfite method:
Citral is more reactive than citronellal due to the presence of double
bond. So it reacts with dilute NaHSO3 solution while citronellal reacts
only with concentrated solutions giving derivatives from which it could
not be regenerated easily.
Preparation: Citral a and b can be easily prepared from geraniol and
nerol by oxidation.
C-Oxygenated Terpenes
2-Aromatic aldehyde:
CHO
Benzaldehyde
B e n z a ld e h y d e
Source: It occurs combined as amygdalin glycoside mainly in bitter almond,
but also in peach and apricot kernels (Rosaceae). Free benzaldehyde is a
constituent of oils of cinnamon.
Isolation: Enzymatic hydrolysis of the glycoside amygdalin which yields
benzaldehyde + glucose + HCN (or benzaldehyde cyanohydrin + glucose).
H OGlc -Glc
C CHO
CN
e m u ls in
+ H 2O + 2 G lc + HCN
A m y g d a lin B e n z a ld e h y d e
H OH
H 2O C
e m u ls in CN
+ 2 G lc
B e n z a ld e h y d e
c y a n o h y d r in
Benzaldehyde
Semi-synthesis: By oxidation of benzyl alcohol or from toluene.
Properties: Benzaldehyde is a liquid, with bitter almond odor that is readily
oxidized on exposure to air to the solid benzoic acid.
Uses: Perfumes industry.
CH 2 OH CHO
[O]
B e n z y l a lc o h o l B e n z a ld e h y d e
CH 3 CHCl 2 CHO
[Cl 2 ] Fe/H 2 O
o
100C
T o lu e n e B e n z y ld ic h lo r id e B e n z a ld e h y d e
C-Oxygenated Terpenes
2-Aromatic aldehyde: CHO
Vanilline OCH 3
OH
V a n illin
Source: It occurs combined as glucovanillin glycoside in vanilla
fruits (pods), which contain about 1.5 – 3% vanillin .
•It occurs in the free form as a constituent of benzoin, balsam
Peru, clove oil.
CHO
Uses: As a flavoring agent in food industry. E n zy m e
CHO
Semi-synthesis: Vanillin can be prepared
H 2O
By oxidation of lignin. OCH 3 OCH 3
NOTE: Ethyl vanillin (vanillal, Ethavan® ,Ethovan®) OGlc OH
It is a solid with a finer and more intense G lu c o v a n illin V a n illin
vanilla-odor than vanillin. Replacement of the
methyl group by an ethyl group intensifies
H CHO
HC C C......
the fragrance. CHO [O]
OCH OCH
3
3
OH OH
OCH 2 CH 3
OH Lignin Vanillin
E th y l v a n illin
C-Oxygenated Terpenes
2-Aromatic aldehyde:
Cinnamaldehyde
Source: Oil of cinnamon (40-50%).
Uses: Cinnameldehyde is a safe and effective insecticide and agro-
pesticide.
2- Potent anti microbial agent, so it is widely used as an ingredient in
several mouthwashes.
3- Could protect against hyperglycemia and obesity.
4- Recent studies indicated it efficacy in protection against Alzehimer’s
disease (Block tau protien formation in the brain).
C- Oxygenated terpenes: Ketones in volatile oils
O OH
O O O
O
(-)-Menthone (+)-Pulegone (+)-Piperitone (-)-Carvone Diosphenol
O
O O
O
(+)-Thujone (+)-Fenchone (+)-Camphor -Irone
Examples of ketones detected in volatile oils
C-Oxygenated Terpenes
3-Monocyclic ketones:
Menthone 1
*
1
*
O O
4 * 4 *
(-)-Menthone (+)-Isom enthone
Source: Oil of pippermint (10-15%).
Isolation: Isolated through formation of its oxime and regenerated by
treatment with dilute H2SO4.
Uses: Flavoring agent.
O O
Carvone
(+ )-C a rv o n e (-)-C a rv o n e
Source: Oil of caraway (45%).
Properties: l-carvone occurs in spermint oil (with peppermint like odor),
while d-carvone occurs in caraway (caraway like odor).
C-Oxygenated Terpenes
3-Monocyclic ketones:
OH
Diosphenol
O
Source: It is the main constituent of leaf oils of
Barosma betulina (Buchu camphor). D io s p h e n o l
Isolation: By repetitive cooling of the oil at – 20º C,
where upon diosphenol separates as crystals.
Uses: 1- Diuretic and urinary antiseptic.
2- Could be use as anti-obesity agent.
Camphor
O
(+ )-C a m p h o r
Source: found in all parts of the camphor tree .
Isolation: By cooling of camphor oil.
Semi-synthesis: It can be prepared from α-pinene.
Camphor
Cl OH
Cl O
H C l gas Is o m e r iz a t io n KOH HNO 3
-1 0 o C M o le c u la r O x id a t io n
R e a ra n g e m e n t
P in e n e P in e n e h y d ro c h lo rid e B o r n y l c h lo r id e B o rn eo l C am phor
Uses: Rubefacient, and local aneshetic.
How can you separate camphor from borneol mixture?
