Equilibrium Studies on Enantioselective Extraction of Oxybutynin Enantiomers by Hydrophilic β-Cyclodextrin Derivatives

The enantioselective extraction of hydrophobic oxybutynin (OBN) enantiomers by hydrophilic beta-cyclodextrin (beta-CD) derivatives was studied. The efficiency of extraction depends strongly on a number of process variables such as types of organic solvents and beta-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 beta-CD. Important parameters of this model were determined experimentally. The physical distribution coefficients for molecular and ionic OBN were 4.96 x 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-beta-CD concentration of 0.1 mol/L was obtained with enantioselectivity (alpha) of 1.26, which was close to the theoretical maximum of 1.32 and performance factor (pf(i)) of 0.036. The model was verified experimentally with excellent results. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 3027-3036, 2011