Kinetic study on reactive extraction for chiral separation of oxybutynin enantiomers

This paper reports the kinetics of the reactive extraction of oxybutynin (OBN) enantiomers by hydroxypropyl-β-cyclodextrin (HP-β-CD) in water as diluent. The kinetic experiments were carried out in a modified Lewis cell, in which hydrophobic OBN enantiomers was initially dissolved in the organic solvent and extracted into the aqueous phase by HP-β-CD. The effects of process parameters including agitation speed, interfacial area, initial concentration of OBN enantiomers, initial concentration of extractant and pH value of aqueous phase, on initial extraction rate were separately studied. Results show that the extraction reaction kinetics is fast. The reactions are first order with respect to OBN and second order with respect to HP-β-CD. The forward rate constants are 6.12 × 10−5 m6/(mol2 s) for R-OBN and 1.13 × 10−4 m6/(mol2 s) for S-OBN, respectively. By comparison of the experimental values with the model predictions, it is found that the model predictions are in good agreement with the experiment.

► The reactions between OBN enantiomers and HP-β-CD fall in regime 3. ► The reactions are first order to OBN and second order to HP-β-CD, respectively. ► The forward rate constant for R-OBN is 6.12 × 10−5 m6 mol−2 s−1. ► The forward rate constant for S-OBN is 1.13 × 10−4 m6 mol−2 s−1. ► The extraction model predictions are in good agreement with the experiment.