Equilibrium studies on enantioselective liquid-liquid extraction of homophenylalanine enantiomers with metal-BINAP complexes

摘要

Enantioselective liquid-liquid extraction of homophenylalanine (Hph) enantiomers was investigated with metal-BINAP complexes as enantioselective extractants. The metal complexes were synthesized by the complexation of (s)-2,2'-Bis(diphenylphosphino)-l,l'-binaphthalene (BINAP) with different central ions, among which, copper(I) complex allowed the separation of the Hph enantiomers with the highest operational selectivity. Efficiency of the extraction depends, often strongly, on a number of process variables, including types of organic solvents, pH of the aqueous phase, concentration of host and substrate, and temperature. In order to better understand the extraction process, equilibrium of the system were modeled by a homogeneous reaction model and an interfacial reaction model, respectively. Important parameters required by the modeling, such as complexation equilibrium constant and physical distribution coefficients were determined experimentally. When coupled with the parameters, extraction performance can be predicted by the models. Comparison between the experimental values and the model predictions indicates that the homogeneous reaction model can predict more accurately. By modeling and experiment, an optimal extraction condition concerning pH of 8 and host concentration of 2 mmol/L was obtained with high enantioselective (a) of 1.837 and performance factor (pf) of 0.086.