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Resolution of racemic mixture
1. RESOLUTION OF RACEMIC MIXTURE
BY
IQRAR AHMAD ABRAR AHMAD
Department Of Pharmaceutical Chemistry
M.Pharm First Year(Sem 1)
RCPIPER,shirpur
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2. ENANTIOMERS:
Isomers which are nonsuperimposable mirror images of each
other are called enantiomers.
These are distinguished by
1)+/-
2)D/L
(l/-)-enantiomer
(anticlockwise rotation)
(dl/±)-racemate
(no overall effect)
(d/+)-enantiomer
(clockwise rotation)
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3. RACEMIC MIXTURE: A equimolar(50/50) mixture of the two
enantiomers is called a racemic mixture or a racemate.
Enantiomers have identical chemical and physical properties,
except:Their effect on plane polarised light.
RESOLUTION: the process of seperation of pure enantiomer from
their racemic modification is called resolution.
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4. NEED FOR RESOLUTION OF RACEMIC
MIXTURE:
CETRIZINE
levocetirizine has been found to be less sedating than
cetirizine
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5. LEVODOPA
levodopa (L-dopa) is used in treatment of Parkinson’s disease, its
D-form causes serious side effects,such as granulocytopenia
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7. 1.MECHANICAL SEPARATION OR
SPONTANEOUS RESOLUTION:
This invoved mechanical separation of the crystal of one enantiomers
from the other in racemic mixture based on difference in their shapes
Crystal of the two forms have different shapes separated by
magnifying lens and forceps
This method first used by pasteur for he resolutiuon of sodium
ammonium tartarate which crystallise out in the form of racemic
mixture below 27 degree
This methods is time consuming and every compound can not be
crystallized at room temperature
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8. 2.PREFERENTIAL CRYSTALIZATION BY
INOCULATION:
This method involve seeding of a saturated solution of the racemic
mixture with a pure crystal of one the two enantiomers.
The soluition now become suppersaturated with respect to the added
enantiomers
It begins to crystallise out
Eg. Harda obtained free from amino acid by adding corresponding
d/l isomers of amino acid
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9. 3.BIOCHEMICAL SEPARATION:
It was introduced by PASTEUR in 1858.
This method is based on fact that when certain micro organisms like
bacteria,fungi,yeast,moulds,etc are grown in dilute solution of racemic
mixture,they eat up one enantiomer rapidly than other.
Example: the mould penicillium glaucum preferentially destroys the
(+) isomer of racemic ammonium tartarate leaving (-) ammonium
tartarate in solution.
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10. 4.CHROMATOGRAPHIC SEPERATION:
The racemic mixture can be separated by chromatography on an
optically active support.
The diastereomeric adsorbates which are formed have different
stabilities.
Thus one enantiomer will be held more tightly than the other and
would be eluted first.
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11. 5.KINETIC METHOD :
This method is based on the fact that one of the enantiomer of racemic
mixture reacts faster than other with optically active compound.
menthol reacts faster with (+) mandelic acid than with (-) mandelic
acid.
Thus with difference in kinetics of reaction,racemic mixture can be
seperated.
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12. 6.PRECIPITATION:
This method is based on formation of precipitate by reaction between
any reagent and racemic mixture.
Example: (+) & (-) narcotine when dissolved in HCL ,precipitates
(+) narcotine.
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13. 7.BY DIASTEREOMERS:
When racemic mixture is allowed to interact with optically active
material, it give a diastereomeric derivatives.
Diastereomer have different physical properties and hence can
easily separated into two component by fractional crystallisation
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