Kinetic study on enhanced reactive extraction separation of terbutaline enantiomers by hydrophobic phase transfer

This paper reports a complex kinetic study on enhanced reactive extraction separation of terbutaline (TBTL) enantiomers by hydrophobic phase transfer. The hydroxypropyl-β-cyclodextrin (HP-β-CD) was selected as hydrophilic chiral selector to preferentially combine the S-TBTL enantiomer in the aqueous phase and the sodium tetraphenylborate (NaTPB) was used as hydrophobic phase transfer reagent to transfer more R-TBTL enantiomer into the organic phase. A specific kinetic model was derived and established for describing the complex chiral extraction process. In the model, the inclusion reaction of TBTL enantiomers with HP-β-CD in the aqueous phase was assumed in equilibrium, and the phase transfer reaction of TBTL enantiomers with NaTPB in the phase interface was controlled by kinetic factors. The different conditions such as agitation speed, interfacial area, and concentration of TBTL, HP-β-CD, and NaTPB were investigated, separately. The forward and backward rate constant of the extraction reaction was 1.49 × 10−6 m4/(mol s) and 2.33 × 10−9 m4/(mol s), respectively. The experimental data were in good agreement with the model predicted results, which confirmed the model assumptions that the phase transfer reaction has not chiral recognition functions but improved the distribution of TBTL in the organic phase, and the inclusion reaction provided the enantioseparation ability.