Solid-Liquid Phase Equilibria of N-Methylephedrine Enantiomers in Two Chiral Solvents

The ternary solubility phase diagrams of the N-methylephedrine species in two chiral solvents, (S)-ethyl lactate and (2R,3R)-diethyl tartrate, have been studied. Solubility measurements were performed for enantiomeric compositions and temperatures ranging from l:1 mixtures to the pure enantiomer and from (273 to 313) K. Predicted ideal solubility curves of the N-methylephedrine species in both solvents revealed deviations from experimental data. The nonrandom two-liquid model was applied to quantify and parametrize these nonidealities and nonideal heterochiral interactions among the enantiomers by means of corresponding activity coefficients. The solvent-solute interactions were interpreted as nonchiral specific, since no asymmetry in the chiral systems were found. The selection of an appropriate solvent for a crystallization-based enantioseparation based on the shape of solubility isotherms is discussed.