This document discusses the resolution of a racemic mixture of menthol. It begins by defining a racemic mixture as a solution containing equal amounts of both enantiomers of a compound. Common methods for separating the enantiomers include mechanical separation, biochemical separation, and forming diastereomeric salts with a resolving agent. For menthol specifically, the document describes two methods - crystallization without solvent and crystallization with hexane as the solvent. Both methods use (R,R)-DBTA as the resolving agent, which forms crystalline complexes that separate the (1R,2S,5R)-menthol enantiomer from the other.

1. RACEMIC MIXTURE SEPARATION
(MENTHOL)
Madhura N. Chincholi
14CHE2032
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2. RACEMIC MIXTURE?
 A solution in which both enantiomers of a
compound are present in equal amounts
 Racemic mixtures can be symbolized by a (d/l)- or
(+/-)- prefix in front of the substance's name.
 The separation of a racemic mixture in to dextro
and laevo components is termed resolution.
 Due to identical physical properties their separation
cannot be effected by simple physical methods.
 Usual methods used for resolving racemic
compounds are Mechanical Separation,
Biochemical separation and by means of salt
formation.
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3. RESOLUTION BY CRYSTALLIZATION
 The racemic compound is reacted with a resolving
agent
 So the mixture contains three chiral compounds:
the two enantiomers and another chiral compound.
 At this time the more stable diastereoisomer
crystallizes and it can be separated from the non
racemic enantiomeric mixture by several methods.
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The essential processes of enantiomeric separation starting from the
racemic compound

5. MENTHOL
5
(+)-Menthol (-)- Menthol
IUPAC name : (1R,2S,5R)-2-Isopropyl-5-methylcyclohexanol
•Menthol has local anesthetic and counterirritant qualities.
•Widely used to relieve minor throat irritation.

6. RESOLUTION OF RACEMIC MENTHOL(MEN)
1. Crystallization without any solvent
 The mixture of resolving agent(RA) and racemic
compound should be warmed until it melted
 Then it should be cooled while one of the
diastereoisomers crystallizes from the melt.
 RA : O,O’-dibenzoyl-(R,R)-tartaric acid ((R,R)-DBTA).
 The crystalline molecular complex (diastereoisomer)
contains the (1R,2S,5R)-menthol (the Lmenthol(L-
MEN))
 While the remained melt is enriched in the other
enantiomer.
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Crystallization without any solvent

8. 2. Crystallization with solvent
 RA : (R,R)-DBTA.
 Solvent : Hexane
 The crystalline molecular complex
(diastereoisomer) contains the (1R,2S,5R)-menthol
(the Lmenthol(L-MEN))
 While the other enantiomer reamined in the solvent.
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9. Crystallization with solvent (hexane)
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10. REFERENCE
E. Pálovics, F. Faigl and E. Fogassy, "Separation of
the Mixtures of Chiral Compounds by
Crystallization", Journal of Advances in
Crystallization Processes, Page 1-37.
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11. THANK YOU!
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