Terpene and structure elucidation of monoterpene

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) 1 st sem

2. TERPENOIDS DEFINATION: Originally, the term “ terpene ” was employed to describe a mixture of isomeric hydrocarbons of the molecular formula C 10 H 16 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 C 5 H 8 2. Monoterpene 2 C 10 H 16 3. Sesquiterpenes 3 C 15 H 24 4. Diterpenes 4 C 20 H 32 5. Triterpenes 6 C 30 H 48 6. Tetraterpenes 8 C 40 H 64 7. Polyterpenes n (C 5 H 8 ) 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: Acyclic monoterpenes. Example- citral. Monocyclic monoterpenes. Example- minthol Bicyclic monoterpenes. Example- camphor 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 Molecular formula- C 10 H 16 O. Presence of 2 double bond as citral is adds on two moles of bromine or hydrogen, this shows that it contain 2 double bond. C 10 H 20 O C 10 H 16 O C 10 H 16 OBr 4 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. 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 . 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 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 t reatment with PBr 3 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.

8. 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 Molecular formula- C 10 H 20 O 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.

9. 5. Synthesis of menthol

10. 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 Molecular formula C 10 H 16 O. Presence of keto group It form oxime with hydroxylamine When champhor is distilled with iodine it yields cavacrol . I 2 +

11. 3. Presence of –CH 2 CO group. When camphor is treated with amyl nitrite and hydrochloric acid, it yields iso nitroso camphor.

12. 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.

13. 6 . Nature of carbon frame in camphor. when camphor is oxidized with nitric acid, it yields a crystalline dibasic acid , camphoric acid C 10 H 16 O 4. 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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