Abstract

Despite the dramatic development of enantioselective synthesis and chromatographic separation methods, optical resolution still remains the cheapest and operationally simplest method for producing pure enantiomers on a larger scale. No extreme conditions or expensive reagents are required, and the eventually expensive resolving agents can be recovered. This chapter is based mainly on the authors’ long experience in the resolution of industrially important molecules, and it presents new observations and establishments as well. Several methods for separation of chiral mixtures, enantiomeric and diastereomeric mixtures, are shown, and possibilities for predicting the efficiency of resolution based on the analysis of physico-chemical properties of the reactants are also described.

Highlights

  • Due to both practical and theoretical reasons, the properties and the possible preparation techniques of chiral compounds are investigated in ever widening fields of research, applying various examination methods [1, 2]

  • The phase-distribution depends on the starting mixture, which follows well the curves of the binary and ternary phase diagrams

  • The equilibrium processes between the supramolecular associates, formed from the chiral molecules, as well as the solubility equilibriums and the catalytic interactions of the formed crystals lead to the phase distribution of the mixtures

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Summary

Introduction

Due to both practical and theoretical reasons, the properties and the possible preparation techniques of chiral compounds are investigated in ever widening fields of research, applying various examination methods [1, 2]. It is a great challenge for some researchers if the goal is to find a simple, inexpensive, economical and patentable preparation of a given chiral compound (single enantiomer), for example according to the demands of the industrial production or drug discovery. Mixtures of diastereomers received with appropriate resolving agents, or mixtures of enantiomers isolated thereof, have to be separated It is common in the two separation methods, that the distribution of the mixtures between two phases, and the phase separation can be applied [4–6]. The most characteristic examples of the above-mentioned methods will be discussed

Formation of macroscopically helical crystals
Particle-size-controlled crystallization
Gravity-based enantiomer separation According to
Fractionated crystallization
Distribution between solid and gas phases, enantiomer separation
Distribution between liquid and gas phases, enantiomer separation
Separation of enantiomeric mixtures by achiral chromatography
Separation of enantiomers by fractionated precipitation
Kinetic control at the fractionated precipitation
Ratio of the molecules composing the diastereomer
Amino acids and their mixtures as resolving agents
Achiral additive structurally related to the racemic compound
Achiral additive structurally related to the resolving agent
Findings
Conclusion
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