Experimental and model study on enantioselective reactive extraction of p-hydroxyphenylglycine enantiomers with metal phosphine complexes

Equilibrium study on enantioselective reactive extraction of p-hydroxyphenylglycine (HPG) enantiomers employing (S)-BINAP-metal complexes as host (selector) was performed in a batch system at 5 °C. A reactive extraction model with an interfacial reaction of HPG enantiomers with (S)-BINAP-metal complexes was established to describe the experimental data. The equilibrium formation constants at the interface and other important parameters were determined experimentally. The extraction system shows good selectivity towards HPG enantiomers. Complex with palladium (PdCl2-(S)-BINAP) exhibits the highest selectivity among the metal complexes studied, which is solubilized in the organic phase and preferentially extracts l-HPG from aqueous phase. Efficiency of extraction depends, often strongly, on a number of process variables, including types of organic solvents and metal precursors, concentration of ligand, pH, and temperature. The model quantitatively predicts extraction performance as a function of key operating parameters, providing a simple computational approach to process optimization. The model was verified experimentally with excellent results.