Methylbenzylamine mandelate

For instance, the aqueous solubility of the n-salt of a-methylbenzylamine mandelate has been reported as 49.1 g/L, and the solubility of the p-salt as 180 g/L [49]. However, the relative solubilities of the p- and n-salt pairs is greatly affected by the choice of temperature or solvent system, and the pathway of the diastereomer separation can easily be manipulated by variations in experimental conditions. In fact, it is possible preferentially to crystallize either the p- or the n-salt depending on the range of parameters used. 

The use of dissociable diastereomers for enantiomer resolution may be illustrated by the case where racemic mandelic acid is resolved using en-antiomerically pure a-methylbenzylamine. The n and p salts of a-methylbenzyl-amine mandelate have aqueous solubilities of 49.1 and 180 g/L, respectively, at 25°C [153], A more recent example, which focuses on the crystallographic origin of the solubility differences, is provided by the resolution of ( )-mandelic acid with (-)-ephedrine in water or methanol solution [154], In general, the relative solubilities of the n and p salt pairs are strongly influenced by the choice of solvent medium and temperature, which provide considerable flexiblity in optimizing the crystallization conditions and the efficiency of resolution. This process may be facilitated by the development of a full solubility phase diagram. 

Many resolving agents derived from natural products have been used since the first discovery of the process, and they are still effective. Many examples are described in the literature.17,18 Synthetic resolving agents, such as a-methylbenzylamine, l-phenyl-2-(p-tolyl)ethylamine, and mandelic acid are very important ones, and widely used for the production of various optically active compounds. 

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