Extraction of Alkali Metal and Ammonium Dipicrylaminates into Nitrobenzene in the Presence of Some Acyclic Polyethers

Abstract

The effect of the presence of six different acyclic polyethers (2-glym, 3-glym, 4-glym, PEG 200, PEG 300 and PEG 400), denoted by L, on the distribution of alkali metal dipicrylaminates and ammonium dipicrylaminate (MA) between the aqueous and nitrobenzene phases has been studied. The two-phase system can be quantitatively described by the following five chemical equilibria: Ma+ + Aa- + L0 ↔ MLa+ + Aa-,Ma+ + Aa- ↔ M0+ + A0-, MLA0 ↔ ML0+ + A0-, MA0 ↔ M0+ + A0-, La ↔ L0, for which the respective equilibrium constants Kex(ML+, A-), Kex(M+, A-), Kd0(MLA), Kd0(MA) and KD were determined. The values of Kex(ML+,A-) increase with the increasing crystallographic radius of the M+ ion and with the number of oxyethylene units in the molecule of the ligand, L, in the series 2-glym < 3-glym < 4-glym < PEG 200 < PEG 300 < PEG 400. In addition, it has been demonstrated that the stability of the ML0+ species in the nitrobenzene phase has a maximum value for M+ = Na+ for all the studied ligands. The presence of the polyethers is detrimental to the separation of Cs+ from the other cations, but improves the separation of Na+ from Li+. The extraction selectivities for the K+/NH4+, K+/Li+ and NH4+/Li+ pairs was not significantly affected by the presence of the ligands, except for 2-glym.