Liquid chromatographic resolution of secondary amino alcohols on a chiral stationary phase based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid: Dependence of temperature effect on analyte structure

Two types of secondary amino alcohols were successfully resolved on a liquid chromatographic chiral stationary phase based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid. The secondary amino alcohols containing a secondary amino group connected directly to the stereogenic center were resolved much better than those containing a hydroxyl group attached directly to the stereogenic center. In addition, the dependence of the separation factor (α) on column temperature was exactly opposite for the two different types of secondary amino alcohols. From the thermodynamic calculations based on Van’t Hoff plots, we conclude that the enantioselectivity for the resolution of the secondary amino alcohols containing a secondary amino group connected directly to the stereogenic center is enthalpically controlled while that for the resolution of the secondary amino alcohols containing a hydroxyl group attached directly to the stereogenic center is entropically controlled.