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Determination of Structure of Terpenoid
Prepared byDr. N.GOPINATHAN
ASSISTANT PROFESSORDEPARTMENT OF PHARMACEUTICAL CHEMISTRY
FACULTY OF PHARMACYSRI RAMACHANDRA UNIVERSITY
CHENNAI-116TAMILNADU
INDIA
General structural elucidation
• Determination of molecular formulae of a pure specimen – elemental analysis.
• If it is optically active, its specific rotation is measured. It helps to distinguish the two or more possible structure as in limonene and carvone.
• Analytical method• Synthetic• Physical• Knowledge of a molecular
rearrangement• Synthesis
Nature of oxygen atom
• Hydroxy group• Formation of acetates with acetic
anhydride
Benzoates with 3,5 dinitro benzoyl chloride
Formation of urethane with phenyl iso cyanate
Nature of OH is revealed by esterification rate primary > secondary > tertiary
Carbonyl group
Carbonyl group-It can be ascertained by oxidation to show whether it is a ketone
or aldehyde
Carbon less in number
CH2-C=O group
CH2-C=O groupin ring on oxidation it yield dicarboxylic acid without any loss of carbon atom
Methyl ketone –COCH3
• Detected by haloform reaction –oxidation- it yields acetic acid
COOH group
• Effervescence with sodiumbicarbonate.• Number of cooH group is estimated by
titrating with standard alkali• The point of attachment of COOH to
primary, secondary or tertiary is determined by rate of esterification.
• primary > secondary > tertiary.• Tertiary is difficult to esterify.
Isopropylidene It is determined by ozonolysis to acetone. The amount of acetone is estimated volumetrically and the number of isopropylidene group is determined
Isopropenyl
Presence of unsaturation is ascertained by addition product.
From number of consumption of H2 molecule the number of double bond can be estimated
The number of halogen consumed would give the amount of unsaturation
Markovnikoff’s rule
Tilden’s reagent
It forms crystalline product having sharp melting point and be used for identification and separation of terpenoids.C=C both are tertiary gives blue colour.One is tertiary and other is secondary gives colourless complex
Epoxide formation by treated with peracid
Presence of conjugated system can be determined by the Diel’s alder reaction
Number of rings
• From number of olefinic double bonds, nature of functional groups and molecular formula of terpenoid, It is possible to find out the molecular formula of the parent saturated hydrocarbon.
Example
• Citral C10H16O with two double bond and one carbonyl group. The molecular formula of the parent saturated hydrocarbon.
It is considere with acyclic general formulae thus citral must be Acyclic
From molecular refraction, the nature of carbon skeleton of sesquiterpenoids can be ascertained
Oxidative degradation product• Degrade the terpenoid to small fragments of known
structure it can be done by oxidation.• Ozonolysis• The reagent attack olefinic linkage of molecule to
form ozonide which upon decomposition by hydrolysis or catalytic reduction yield the corresponding carbonyl carbon.
• Ozonolysis locate position of double bond in a molecule.
• The formation of acetone and formaldehyde reveals the presence of isopropylidene and terminal double bond
Oxidation with nitric acidIt is a strong oxidising agent which drastically degrade the terpenoid to a mixture of aliphatic and aromatic acid
Haloform reaction
Hydroxylating agent – lead tetra acetate in hot acetic acid, peracid , Osmium tetra oxide, hydrogenperoxide, potassium per manganate etc It will form glycols
If double bond is in ring on oxidation yield ketoacid or dicarboxylic acid without loss of carbon atom.Alpha pinene on oxidation yield keto acid
Dehydrationwhen terpenoid with alcohol or ketonic group heated with dehydrating agent, these lose a molecule of water and converted into simple aromatic compound
When open chain terpenoids are dehydrated with dehydrating agent they yield cyclic compound
Dehydrogenation
• When terpenoid is heated with Zn, I, Br,S,Se and palladium they are converted into aromatic compound of known structure.
• If it is unknown which can be determined by synthesis.
• By this method the skeleton structure and position of side chain in original terpenoids can be determined.
Dehydrogenation
Synthetic method
Grignard reagent
By grignard reaction methyl, isopropyl can be introduced to carbonyl alpha terpineol a naturally occurring terpenoid tertiary alcohol can be prepared
Reformatsky reaction- alpha substituted ester treated with carbonyl [ aldehyde / ketone / ester ] in the presence of zinc to form beta hydroxy ester.later which is treated with dilute acid to yield beta hydroxy acid which may further converted to unsaturated acid or hydrocarbon
Physical methods
• UV- detection of conjugation.• IR• NMR• Mass spectroscopy• Optical rotation• X ray analysis• Knowledge about rearrangement• synthesis
THANK YOU