Extraction of alkaline-earth metal ortho- and para-nitrophenoxides from aqueous media by crown ether and cryptand complexing agents

Abstract

A study has been performed on the extraction of alkaline-earth metal ortho- and para-nitrophenoxides, from aqueous medium into methylene chloride, in the presence of crown ether and cryptand complexing agents. The results are analyzed in terms of the various constituent complexation and extraction equilibria involved. Comparison is drawn with our previously reported study on extraction of potassium p-nitrophenoxide. The different anion stoichiometries in the two systems result in relatively more favorable extraction of M+ systems at low anion concentrations. Furthermore, while extraction of MX (X = o- or p-nitrophenoxide) can be carried out in the presence of excess MOH, this is not possible in the case of MX2 due to the limited solubility of M(OH)2. The addition of excess MOH leads to more efficient extraction of M+-phenoxides and prevents hydrolysis to free phenols. A noteworthy point in both MX and MX2 systems is that at high concentrations of complexing agent a saturation effect occurs, which limits the overall extent of extraction achievable. Under these conditions the extraction is governed by the equilibrium constant, Kdcs, representing the partitioning of the complexed salt between the aqueous and organic phases, and is independent of the amount of ligand present.