THE SOLVENT-EXTRACTION OF ALKALI-METAL PICRATES WITH 4,13-N,N'-DIBENZYL-4,13-DIAZA-18-CROWN-6

Extraction of alkali metal picrates with N,N'-dibenzyl-18-crown-6 was carried out, with dichloromethane as water-immiscible solvent, as a fu nction [ligand]/[metal cation]. The extractability of metal picrates ( Li+, Na+, K+ Rb+, Cs+) was evaluated as a function of [L]/[M+]. The ex tractability of complex cation-picrate ion pairs decreases in this seq uence: 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 degrees C. The values of the extraction constants (log K-ex) we re 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 extractabi lity against Li+ compared to the other metal picrates, whereas it show s no obvious extractability difference amongst the other metal cations when [L]/[M+] is 0.2-1. However, an increasing extractability is obse rved for Cs+ when [L]/[M+] [1]. (C) 1998 Elsevier Science B.V. All rig hts reserved.