Removal of chromate and phosphate anion from aqueous solutions using calix[4]aren receptors containing proton switchable units

In the present study four new calix[4]arene amide ionophores (4-7) have been prepared by aminolysis of calix[4]arene diester (3) and investigated their extraction ability toward phosphate and dichromate anions at different pH. The 1H NMR data showed that the synthesized compounds exist in the cone conformation. Liquid-liquid extraction experiments have been performed to evaluate the dichromate and phosphate anions extraction efficiency of both calix[4]arene bearing amide-pyridinium units (4-7) and the calix[4]arene derivative bearing aminomethyl pyridinium units (8, 9). It was observed that, compounds 4-7 exhibited lower affinity toward phosphate ions than the calix[4]arene derivative bearing amine pyridinium units (8, 9). The extraction of phosphate and dichromate anions by these compounds indicates that the partially protonated pyridyl or amino groups play the major role for the formation of hydrogen bonds and electrostatic interactions.