Enantiomeric separation of methyl mandelate by gas chromatography and discussion the chiral recognition mechanism

Objective:To separate the enantiomers of methyl mandelate by gas chromatography and investigate the process of the enantiomers separation and the chiral recognition mechanism by calculation of thermodynamic parameters in process of enantiomeric separation.Methods:The enantiomers of methyl mandelate had been separated on β-cyclodextrin(Cyclodex B)chiral capillary chromatographic column.Results:The enantiomers of methyl mandelate can be baseline separated at β-cyclodextrin(Cyclodex B,30 m×0.25 mm×0.25 μm)chiral capillary chromatographic column under column temperature 118 ℃ and 1 mL·min-1 of flow rate of carrier gas.The separation factor(α)and separation degree(R)of enantiomers of methyl mandelate were 1.02 and 1.55,respectively.There was good linearity relation between enantiomeric lnk' or lnα and 1/T.Enthalpy-change(ΔH)of(R)-and(S)-methyl mandelate calculated from Van't Hoff curve were-59.29 kJ·mol-1和-60.64 kJ·mol-1,respectively.The differential enthalpy-change [Δ(ΔH)] and differential entropy-change [Δ(ΔS)] between(S)-and(R)-methyl mandelate calculated from Vant't Hoff curve were-1.34 kJ·mol-1和-3.25 J·mol-1·K-1,respectively.Conclusion:The separation of enantiomers of methyl mandelate was enthalpy-driven process and the interaction between surfaces out of the cavity of β-cyclodextrin and methyl mandelate might mainly contribute to the separation.