The solvent extraction of alkali metal picrates with 4,13- N, N′-dibenzyl-4,13-diaza-18-crown-6

Abstract

Extraction of alkali metal picrates with N, N′-dibenzyl-18-crown-6 was carried out, with dichloromethane as water-immiscible solvent, as a function [ligand]/[metal cation]. The extractability of metal picrates (Li +, Na +, K +, Rb +, Cs +) was evaluated as a function of [L]/[M +]. The extractability of complex cation–picrate ion pairs decreases in this sequence: Li +>Rb +>Cs +>K +>Na +. The overall extraction equilibrium constants ( K ex) for complexes of N, N′-dibenzyl-18-crown-6 with alkali metal picrates between dichloromethane and water have been determined at 25°C. The values of the extraction constants (log K ex) were determined to be 10.05, 6.83, 7.12, 7.83, 6.73 for Li +, Na +, K +, Rb + and Cs + compounds, respectively. DB186 shows almost 2-fold extractability against Li + compared to the other metal picrates, whereas it shows no obvious extractability difference amongst the other metal cations when [L]/[M +] is 0.2–1. However, an increasing extractability is observed for Cs + when [L]/[M +] [1].