Metal-ion Complexation of Noncyclic Poly(oxyethylene) Derivatives. I. Solvent Extraction of Alkali and Alkaline Earth Metal Thiocyanates and Iodides

The reaction of noncyclic poly(oxyethylene) derivatives with alkali and alkaline earth metal ions was investigated by means of the solvent extraction of their thiocyanates or iodides. Polyethylene glycols with more than 23 oxyethylene units showed a strong extracting power comparable to those of the crown ethers, and the power increased with the increasing number of oxyethylene units in them. Extraction studies using homogeneous poly(oxyethylene) monododecyl ethers revealed that more than 7 oxyethylene units were necessary to bind the potassium ion in the water phase and to transfer the complexed salt to the organic phase, and that the extracting ability of octa(oxyethylene) monododecyl ether was about one sixth of that of 18-crown-6. The monododecyl ether is fairly effective as a complexing agent for potassium picrate even below its critical micelle concentration; the stoichiometry of the extractable complex was found to be 0.8:1 with respect to the ether and the picrate. There was no remarkable difference in the selectivity for alkali metal ions between noncyclic poly (oxyethylene) derivatives and 18-crown-6.