This presentation contains introduction of terpene and structure elucdation of monoterpenes

1. STRUCTURE ELUCIDATION
OF MONOTERPENOIDS
DEPARTMENT OF
PHARMACEUTICAL CHEMISTRY
ISF College of Pharmacy, Moga
Shalini Jaswal
M.Pharm (Pharmaceutical Chemistry)
1st sem

2. TERPENOIDS
• DEFINATION: Originally, the term “terpene” was employed to describe
a mixture of isomeric hydrocarbons of the molecular formula C10H16
occurring in the terpentine and many essential oils which are obtained from
the sap and tissues of certain plant and trees. The oxygenated derivatives
like alcohols, aldehydes, ketones, etc. at that time called camphor.
• CLASSIFICATIONS:
Class No. of isoperene
units
Molecular
formula
1. Isoprene 1 C5H8
2. Monoterpene 2 C10H16
3. Sesquiterpenes 3 C15H24
4. Diterpenes 4 C20H32
5. Triterpenes 6 C30H48
6. Tetraterpenes 8 C40H64
7. Polyterpenes n (C5H8)n

3. MONOTERPENOIDS OR TERPENES
• The monoterpenoids are composed of two isoperene units. These are the
simplest natural occurring terpenoids which are isolated from essential oils
obtains from the leaves, roots and barks of various plant.
• These compounds have pleasant odours and are largely used as perfumery
industry.
• Monoterpenoids may be divided into three groups:
1. Acyclic monoterpenes. Example- citral.
2. Monocyclic monoterpenes. Example- minthol
3. Bicyclic monoterpenes. Example- camphor
A. CITRAL
• It is considered to be the most important
member of the acyclic monoterpenes because
the structure of remaining terpenoids in this group are based on the
structure of citral.
• It is optically inactive oil with lemon like smell.
• Pale yellow in colour, b.p. 228
.
C

4. ISOLATION
From lemon grass oil, citral is obtained by its fractional distillation under
reduced presssure. This is then purified by forming the bisulphite compounds
the latter compounds further decomposed with sodium bicarbonate yields, pure
citral
CONSTITUTION OF CITRAL
1. Molecular formula- C10H16O.
2. Presence of 2 double bond
• as citral is adds on two moles of bromine or hydrogen, this shows that it
contain 2 double bond.
C10H20O C10H16O C10H16OBr4
tertrahydrocitral citral citral tetrabromide
• Citral on ozonolysis yields acetone, laevuladehyde and glyoxal. This shows
that citral is an acyclic compounds containing 2 double bond.

5. 3. Presence of aldehyde group
• With hydroxylamine, citral forms an oxime, indicating that it must contain
one oxo group.
• With phenylhydrazine, it forms phenylhyrazone, further conferming the
presence of oxo group.
• Citral on reduction with sodium amalgum yields alcohol, geraniol. Which
indicates that the oxo group is aldehyde.
4. C-Skeleton of citral
when citral is heated with pottasium hydrogen sulphate, it cyclises to p-
cymene, a cyclic compound of known structure.

6. Formation of p-cymene and the products obtained from the ozonolysis reveal
that C-skelton of citral contains two isoprene units which joined by heat to
tail arrangement. The formation of p-cymene also reveals that relative
positions of methyl and isopropyl groups in citral.
5. Structure of citral
6. Synthesis of citral
Barbier-Bouveault-Tiemann’s synthesis:
According to this synthesis, methyl heptenone is converted into geranic
ester by using Reformatsky’s reaction(is an organic reaction which condence
aldehyde or ketone, with alpha-halo esters using a metallic zinc to form beta-
hydroxyester.).

7. After this, Tiemann converted geranic ester into citral by distilling a mixture of
calcium salts of geranic and formic acid.
Arens-Van Dorp’s synthesis:
In this synthesis, acetone on condensation with acetylene in the presence of
Sodium and liquid ammonia yield the product which on reduction followed by
treatment with PBr3 undergoes allylic rearrangement. The product so obtained
is treated with sodium salt of aceto- acetic ester and then hydrolysed to yield
Methyl heptone . The latter compound on condensation with ethoxy acetylene
magnesium bromide, followed by the partial reduction and acidification yields
Citral by allylic rearrangement.

9. B. MENTHOL
• Menthol is an optically active compound.
• Only its (-) form occurs naturally in peppermint oils.
• It’s a saturated compound having melting point 43
.
C.
• It is used as an antiseptic and an aesthetic.
Constitution
1. Molecular formula- C10H20O
2. Presence of alcoholic group - as menthol forms esters readily with acids,
this means that it must posses an alcoholic group.
3. Presence of secondary alcohol
The oxidation of menthol yields ketone, indicating that the hydroxyl group
in menthol is secondary in nature.
4. On dehydration followed by dehydrogenation, menthol yields p-cymene,
indicating the presence of p-cymene Skelton in the compound.

10. 5. Synthesis of menthol

11. C. CAMPHOR
• It is the most important constituent of the oil of the camphor.
• Occure in the Cinnamonum camphora.
• It is solid having melting point 180
.
C and it is optically active
• Uses – as an insect repellent.
- as an mild disinfectant and stimulant for heart muscles.
- for the production of smokeless powders and explosives.
• Constitution of Camhor
1. Molecular formula C10H16O.
2. Presence of keto group
I. It form oxime with hydroxylamine
II. When champhor is distilled with iodine it yields cavacrol.
I2 +

12. 3. Presence of –CH2CO group.
When camphor is treated with amyl nitrite and hydrochloric acid, it yields iso
nitroso camphor.

13. 4. Presence of six memberd ring
5. Saturated characteristics.
Camphor forms monosubstituted products like mono-bromocamphor, mono-
chlorocamphor-sulphonic acid. The production of these products revels
that camphor is a saturated compound. And does not contains a double
bond.

14. 6. Nature of carbon frame in camphor.
when camphor is oxidized with nitric acid, it yields a crystalline
dibasic acid , camphoric acid C10H16O4. as a camphoric acid
possesses the same number of carbon atom as camphor , it means
that the keto group must be present in one of the ring of
camphor. Further camphoric acid is dicarboxlic acid and its
molecular refraction reveals that it is also saturated. Thus during
the conversion camphor into camphoric acid , there occur the
opening of ring containing the keto group and therefore
camphoric acid must be monocyclic compound.
When camphoric acid is further oxidized with nitric acid ,
camphoric acid is obtained.

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