Thermodynamic study of solvent extraction of monovalent metal picrates with benzo-18-crown-6 into chloroform

Thermodynamic parameters (H_ex⁰ and S_ex⁰) for the overall extractions of monovalent metal (Na, K, Rb, and Tl) picrates with benzo-18-crown-6 (B18C6), and those (H_D,L⁰ and S_D,L⁰) for the distribution of B18C6 were determined between chloroform and water. All the extracted B18C6 complexes were l:1:1 complexes (B18C6:metal ion: picrate anion). The H_ex⁰ and S_ex⁰ values for all the metals are negative. Every extraction of the metal picrate with B18C6 is completely enthalpy driven. The H_D,L⁰ and S_D,L⁰ values of B18C6 are both positive, and the partition of B18C6 is entirely entropy driven. Enthalpy (H_ex,ip⁰) and entropy changes (S_ex,ip⁰) for ion-pair extractions of B18C6-metal ion complexes with picrate anions were calculated. All the H_ex,ip⁰ and S_ex,ip⁰ values are negative, and the ion-pair extractions are completely enthalpy driven.