**Section 1**

**Chiral Crystallization** 

X Contents

I wish to thank all the authors for their contributions for this book and it is my pleasure to acknowledge the assistance of Ms Vana Persen for her assistance during

Finally I would like to acknowledge my family who has supported me through all the years of doing science. To my wife Dina von Schwarze and to our children Michael,

Department of Chemistry and the Institute of Nanotechnology

**Prof. Yitzhak Mastai** 

Israel

Bar-Ilan University, Ramat-Gan,

the write-up of this book and is preparation in final format.

Reut and Noa for their patience and support.

**1** 

*Hungary* 

**Separation of the Mixtures of Chiral** 

Emese Pálovics2, Ferenc Faigl1,2 and Elemér Fogassy1\*

Reaction of a racemic acid or base with an optically active base or acid gives a pair of diastereomeric salts. Members of this pair exhibit different physicochemical properties (e.g., solubility, melting point, boiling point, adsorbtion, phase distribution) and can be separated owing to these differences. The most important method for the separation of enantiomers is

Preparation of enantiopure (ee~100%) compounds is one of the most important aims both for industrial practice and research. Actually, the resolution of racemic compounds (1:1 mixture of molecules having mirror-imagine relationship) still remains the most common method for producing pure enantiomers on a large scale. In these cases the enantiomeric mixtures or a sort of their derivatives are separated directly. This separation is based on the fact that the enantiomeric ratio in the crystallized phase differs from the initial composition. In this way, obtaining pure enantiomers requires one or more recrystallizations. (Figure 1). The results of these crystallizations (recrystallizations) of mixtures of chiral compounds differ from those observed at the achiral compounds. Expectedly, not only the stereoisomer in excess can be crystallized, because the mixture of enantiomers (with mirror image relationship) follows the regularities established from binary melting point phase diagrams, and ternary composition solubility diagrams, respectively, as a function of the starting enantiomer proportion. According to this fact, we talk about conglomerate behaviour when the enantiomeric excess is

At the same time, there are some enantiomeric mixtures having racemate properties (based on binary phase diagram) which show conglomerate behaviour during its purification by fractionated precipitation. Always the enantiomeric excess is crystallized independently from the starting isomeric composition. This is explained by the kinetic crystallization of the enantiomeric excess.2 Consequenlty, if the enantiomeric purity obtained after recrystallization or by other partial crystallization (as the result of splitting between the two phases) is

crystallized, and racemate behaviour when it remains in the mother liquor.1

**1. Introduction** 

 \*

Corresponding Author

the crystallization. This is the subject of this chapter.

**Compounds by Crystallization** 

*1Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, 2Research Group for Organic Chemical Technology,* 

*Hungarian Academy of Sciences, Budapest,* 
