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Resolution of Enantiomers

Resolution of Enantiomers. Separation of a racemic mixture into its two respective enantiomers. Diastereomers. Diastereomers have different physical properties: BP, MP, density, refractive index, solubility

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Resolution of Enantiomers

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  1. Resolution of Enantiomers Separation of a racemic mixture into its two respective enantiomers

  2. Diastereomers • Diastereomers have different physical properties: • BP, MP, density, refractive index, solubility • Can be separated through conventional means (distillation, recrystallization, chromatography) mp = 158oC mp = 256oC

  3. Resolution of Enantiomers • In 1847, Pasteur performed the first resolution of enantiomers from a racemic mixture of tartaric acid salts. • The different enantiomers formed different shaped crystals that were separated by hand using tweezers.

  4. Resolution of Enantiomers • A common method uses a chiral resolving agent. • An optically pure acid forms diastereomeric salts when reacted with a racemic amine, (+/-) bases.

  5. Resolution of Enantiomers • Conversely, an optically pure base reacts with a racemic mixture, (+/-) isomers of acids, to produce diastereomeric salts. • S-(-)-α-phenethylamine can resolve a racemic mixture of ibuprofen, [Ibu(-)][Ibu(+)] (R,S)-2-(4-(2- methylpropyl)phenyl)propanoic acid • S-(-)-α-phenethylamine [Phe(-)] reacts with a racemic mixture of ibuprofen, [Ibu(-)] [Ibu(+)] (R/S) to produce [Phe(-)] [Ibu(-)](S,S) and [Phe(-)][Ibu(+)](S,R), which can be separated.

  6. Ibu(+) Ph(-) Ibu(+) Ibu(-) Ibu(+)Ph(-) 2Ph(-) Ibu(-)Ph(-) Ibu(+)Ph(-) Ibu(-)Ph(-) Ph(-) Diastereomers (different solubilities) Ibu(-) Ibuprofen enantiomers

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