Ternary solubility phase diagrams of mandelic acid and n-methylephedrine in chiral solvents with different carbon chain lengths

Abstract

Ternary solubility phase diagrams of mandelic acid and N-methylephedrine species in chiral solvents, (S)-methyl lactate, (S)-propyl lactate, and (S)-butyl lactate, have been determined. Solubility measurements were performed for enantiomeric compositions ranging from 50:50 mixtures to the pure enantiomers and temperatures ranging from 0 to 35 C for mandelic acid and from 0 to 25 C for N-methylephedrine, respectively. The ternary solubility phase diagrams of mandelic acid and N-methylephedrine showed symmetric behavior. It became obvious that increasing chain length of chiral solvents, i.e. from (S)-methyl lactate to (S)-butyl lactate, resulted in decreasing solubility.1HNMR and Raman spectroscopy have been applied to characterize the solute-solvent interaction in the liquid phase for mandelic acid system. Molecular modeling calculations were performed for mandelic acid to get a deeper understanding of the solute-solvent interactions. The effect of the solvent on the shape of the solubility isotherms is discussed by determining the relative solubility ratios (Rmol-values) ust for N-methylephedrine