Separation and Thermodynamic Studies of Chiral Sulfoxides on Teicoplanin‐Based Stationary Phase

Three different teicoplanin chiral stationary phases (CSPs) (native teicoplanin, teicoplanin aglycon, and methylated teicoplanin aglycon) were used to study the enantioseparation and temperature behaviour of a set of chiral sulfoxides. The chiral analytes studied were 2‐, 3‐, 4‐ toluyl methyl sulfoxides and phenyl methyl sulfoxides with different 2‐, 3‐, 4‐halogen substituents on the aromatic ring. The effect of temperature on the LC separation of racemic aromatic sulfoxides was studied between 10 and 50°C in a methanol mobile phase. The van't Hoff plots were constructed and thermodynamic data were determined from the slope and the intercept of linear van't Hoff plots. The van't Hoff plots (ln k versus 1/T and ln α versus 1/T) were linear for all enantiomers. Given the linearity of the van't Hoff plots, thermodynamic parameters, such as the change in enthalpies Δ(ΔH 2,1) and the entropies Δ(ΔS 2,1) for the sulfoxide enantiomers could be calculated. In addition, the elution order did not reverse in the temperature range of this study and the mechanism of enantioseparation did not vary.