Structural Elucidation of Monoterpenoids

Monoterpenoids or Terpenes:Consist of two isoprene units(C10H16)
Oxygenated derivatives= Isoprenoid compound
Pleasant odour = used for their flavour

Monoterpenoids may be divided into three groups:
1.Acyclic monoterpenoids (Eg.Citral)
2.Monocyclic Monoterpenoids (Eg.menthol)
3.Bicyclic Monoterpens (E.g.Camphor)
Citral:Acyclic Monoterpenes
Other structure based on this structure
Optical Activity: Inactive
Smell: Lemon Like
Colour: Pale Yellow
Boiling Point: 228 ℃

Isolation:From lemon grass (Cymbopogon citratus or Cymbopogon flexuosus).
Fractional Distillation under reduced pressure.
Purified by forming bisulphite.
This compound further decomposed with sodium bicarbonate yields pure citral.
Uses:Used in perfume & flavour industry.
Manufactures of vitamin A.
Used to reduce blood pressureMenthol:Optically active
Saturated compound
Melting point: 43 ℃
Laevorotatory compound
Monocyclic terpenoids
Isolation:
Obtained from peppermint oil(Mentha piperita, .Mentha arvensis)
Family : labiatae
Menthone is another constituent of peppermint oil ,geranium.
Uses:
Both use as
carminative
stimulant
flavouring agent
Antiseptic
Local Anaesthetic
Camphor:Optically active
Melting Point: 180 ℃
Naturally occurring bicyclic monoterpenoid ketone
Dextrorotatory form naturally occurring
Racemic form –synthetic product
Colourless,crystalline solid granular mass
It has characteristic penetrating odour
Aromatic pungent taste followed by sensation of cold
Isolation
Obtained from camphor tree(Cinnamomum camphora)
Family:Lauraceae
Uses
Mild disinfectant
Stimulant for heart muscles
Topically antipruritic agent
Rubefacient
Counterirritant
Antiseptic
Insect repellant
Determination of molecular weight
Flavouring agent in soaps ,tooth powder, cosmetic products
1.Molecular formula: C10H160
2.Presence of saturated system:
Camphor form monosubstituted products like mono-bromocamphor, mono-chloro-camphor-sulphonic acid. The production of these products reveals that camphor is saturated compound. and does not contain a double bond.
3.Presence of cyclic ketonic group:
Hydroxylamine-oxime
Phenylhydrazine-phenylhydrazone
Semicarbazide-semicarbazone .
Oxidation of camphor yields dicarboxylic acid having same number of carbon atoms.
All reactions indicate the presence of a cyclic ketone.

1. Structural Elucidation of Terpenoids Presented By: Divya Ashok Dhule M.Pharm .(Pharmaceutical Chemistry) 1 st year Department of Pharmaceutical Sciences Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur-440033

2. Monoterpenoids or Terpenes Consist of two isoprene units(C 10 H 16 ) Oxygenated derivatives= Isoprenoid compound Pleasant odour = used for their flavour Monoterpenoids may be divided into three groups: 1.Acyclic monoterpenoids (Eg.Citral) 2.Monocyclic Monoterpenoids (Eg.menthol) 3.Bicyclic Monoterpens (E.g.Camphor)

3. Citral : Acyclic Monoterpenes Other structure based on this structure Optical Activity: Inactive Smell: Lemon Like Colour: Pale Yellow Boiling Point: 228 ℃ Fig. Citral (3,7-Dimethyl-2,6-octadienal or lemonal)

4. Isolation From lemon grass (Cymbopogon citratus or Cymbopogon flexuosus ). Fractional Distillation under reduced pressure. Purified by forming bisulphite. This compound further decomposed with sodium bicarbonate yields pure citral . Uses Used in perfume & flavour industry. Manufactures of vitamin A. Used to reduce blood pressure.

5. 1.Molecular formula : C 10 H 16 O 2.Presence of 2 double bond Addition of two moles of bromine & hydrogen It contain 2 Double bond C 10 H 20 O C 10 H 16 O C 10 H 16 OBr 4 Tetrahedrocitral Citral Citral Tetrabromide Citral Acetone,Laevulaldehyde,glyoxal Ozonolysis Structural Elucidation of Citral

6. 3.Presence of an aldehyde group: Citral reduces fehling solution indicate confirming presence of aldehydic group.

7. 4.C-skeleton of citral : When citral is heated with potassium hydrogen sulphate ,it is cyclized to p-cymene ,a known aromatic compound and hence the carbon skeleton and the relative positions of the alkyl groups ,methyl and isopropyl are established.

8. Synthesis : Structure of citral is confirmed by Barbier Bouveault Tiemann’s synthesis.

9. Menthol: Optically active Saturated compound Melting point: 43 ℃ Laevorotatory compound Monocyclic terpenoids

10. Isolation: Obtained from peppermint oil(Mentha piperita, .Mentha arvensis) Family : labiatae Menthone is another constituent of peppermint oil ,geranium. Uses: Both use as carminative stimulant flavouring agent Antiseptic Local Anaesthetic

11. Structural elucidation of Menthol : 1 . Molecular formula : Menthol =C 10 H 20 O Menthone= C 10 H 18 O 2 . Presence of secondary alcoholic group : Menthol 3.Presence of p-menthane skeleton: Dehydrogenation of menthol yields p-cymene indicating the presence of p-menthane skeleton in the compound. Menthone (O)

12. 4. Synthesis :

13. Camphor Optically active Melting Point: 180 ℃ Naturally occurring bicyclic monoterpenoid ketone Dextrorotatory form naturally occurring Racemic form –synthetic product Colourless,crystalline solid granular mass It has characteristic penetrating odour Aromatic pungent taste followed by sensation of cold

14. Isolation Obtained from camphor tree(Cinnamomum camphora ) Family:Lauraceae Uses Mild disinfectant Stimulant for heart muscles Topically antipruritic agent Rubefacient Counterirritant Antiseptic Insect repellant Determination of molecular weight Flavouring agent in soaps ,tooth powder, cosmetic products

15. Structural elucidation of camphor 1.Molecular formula : C 10 H 16 2.Presence of saturated system : Camphor form monosubstituted products like mono- bromocamphor , mono-chloro-camphor-sulphonic acid. The production of these products reveals that camphor is saturated compound. and does not contain a double bond. 3.Presence of cyclic ketonic group: Hydroxylamine-oxime Phenylhydrazine -phenylhydrazone Semicarbazide-semicarbazone . Oxidation of camphor yields dicarboxylic acid having same number of carbon atoms. All reactions indicate the presence of a cyclic ketone.

16. 4.Presence of –CO-CH 2 Benzaladehyde = monobenzylidene derivative which indicate the presence of –CO-CH 2 This is confirmed by the formation of isonitroso derivative (oxime) when treated with nitrous acid(HNO 2 ) Oxidation of camphor to a dibasic acid , camphoric acid ,with the same number of carbon atoms confirms the presence of -CO-CH 2, Distillation of camphorbwith iodine yields Carvacrol.the presence of phenolic group in carvacrol indicates the presence of ketonic group in camphor.

17. 5.Bicyclic skeleton : The presence of ketonic group in camphor (C 10 H 16 O) suggests C 10 H 18 as the molecular formula for the saturated hydrocarbon . The molecular formula C 10 H 16 corresponds to C n H 2n-2 (general formula for bicyclic compounds). Therefore ,the camphor must be bicyclic . 6.Presence of one ring as a six –membered ring : Upon distillation with Zinc chloride or phosphorus peroxide camphor yields p-cymene ,indicating that one of thee rings is six membered in camphor

18. 7.Carbon frame in camphor: When camphor is oxidized with nitric acid ,it produces camphoric acid and then camphoronic acid . Therefore ,in order to determine the structure of camphor.

19. Synthesis: Structure of camphor is confirmed by synthesis

20. Reference: Algarsamy V. , Pharmaceutical Chemistry of Natural Product, Monoterpenoids.Edition 2012, Page no.367-404

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