Terpenoids

Terpenoids

CAMPHORMolecular Formula : C10H16OGeneral reactions showed it is saturated.Oxidation of camphor gave dicarboxylic acid of 10 C atoms which showed the presence of a keto group.Parent hydrocarbon has molecular formula C10H18 which is CnH2n-2, hence it is a bicyclic system.It forms an oxime with nitrous acid, hence it contains CH2CO- group.

Camphoric acid is a dicarboxylic acid which contains same number of C atoms as camphor. Hence in the formation of camphoric acid, the ring containing the keto group has opened and it contains only one ring.

Camphoronic acid was shown to be a saturated tricarboxylic acid and on distillation gave isobutyric acid II, trimethylsuccinic acid III, CO2 and C.

Bredt suggested that camphoronic acid is ,,-trimethyl tricarballylic acid I since this structure would give the required decomposition products.

Camphoronic acid has structure I, hence camphoric acid must contain three methyl groups. The formula can be written as (CH3)3C5H5(COOH)2. The parent hydrocarbon of this is C5H10, which corresponds to cyclopentane derivative.

Camphoric anhydride forms only one monobromo derivative therefore there is only one -H atom. Hence one carboxylic acid has to be at tertiary carbon (C1). The position of other carboxylic acid has to be predicted.

p-Cymene

Distillation of camphor with ZnCl2 gives p-Cymene, which can be expected from the structure B only.AB

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When distilled with iodine camphor gives carvacrol, VIII.

SYNTHESIS of CAMPHORIC ACID

SYNTHESIS of CAMPHOR

LONGIFOLENEMolecular formula : C15H24.The structure was established by the X-ray analysis of its hydrochloride

SYNTHESIS of LONGIFOLENE

ABIETIC ACIDMolecular Formula : C20H30O2.

Its a monocarboxylic acid.

On dyhydrogenation with S it gives retene.

Retene, C18H18 was shown by oxidative degradation to be 1-methyl-7-isopropylphenanthrene (confirmed by synthesis).

Hence the carbon skeleton present in abietic acid is :

It is known that on dehydrogenations with S/Se , carboxyl groups and angular methyl groups are eliminated.

Oxidation of abeitic acid with KMnO4 gives a mixture of products, among which are 2 tricarboxylic acids, C11H16O6 (II), C12H18O6 (III). II on dehydrogenation forms m-xylene and III forms hemimellitene. In both cases 3 carbon atoms are lost which could be 3 carboxylic groups. Hence atleast two methyl groups are in the meta position. One methyl group was originally present in abietic acid in ring A, hence the other methyl group must be an angular one and present at 12 position.

Vocke showed that acid II evolves two molecules of CO2 when warmed with concentrated H2SO4. This indicates II contains 2 carboxyl groups attached to tertiary carbon atoms. These results can be explained by assuming that one carboxyl group in II is that in abietic acid, and since in both cases this carboxyl group is attached to a tertiary carbon atom, the most likely position of this group is 1.

Catalytic hydrogenation of abietic acid gives tetrahydroabietic acid, C20H34O2. Thus it contains two double bonds.

Abietic acid on oxidation with KMnO4, among other products gives isobutyric acid. Hence one double bond is in ring C at 6,7 or 7,8 position. UV spectrum has indicated that the double bonds are not only conjugated but also present in different rings.

If one double bond is at 6,7 position then the other double bond will be in the same ring but if it is at 7,8 position then the other double bond will be at 14,9 position.

SYNTHESIS of ABIETIC ACID

TAXOL