Equilibrium studies on enantioselective extraction of oxybutynin enantiomers by hydrophilic β-cyclodextrin derivatives



The enantioselective extraction of hydrophobic oxybutynin (OBN) enantiomers by hydrophilic β-cyclodextrin (β-CD) derivatives was studied. The efficiency of extraction depends strongly on a number of process variables such as types of organic solvents and β-CD derivatives, concentration of selector, pH, and temperature. The experimental data were described by a reactive extraction model with a homogeneous aqueous phase reaction of R,S-OBN with β-CD. Important parameters of this model were determined experimentally. The physical distribution coefficients for molecular and ionic OBN were 4.96 × 10−3 and 9.52, respectively. The equilibrium constants of the complexation reactions were 1770 and 1340 L/mol for S- and R-OBN, respectively. By modeling and experiment, an optimal extraction condition with pH of 5 and HP-β-CD concentration of 0.1 mol/L was obtained with enantioselectivity (α) of 1.26, which was close to the theoretical maximum of 1.32 and performance factor (pfi) of 0.036. The model was verified experimentally with excellent results. © 2011 American Institute of Chemical Engineers AIChE J, 2011