A comparison of alkali metal cation and alkaline earth cation solvent extraction was made for three additional monoionizable crown ethers and one diionizable crown ether. sym-(n-Octyldibenzo)-16-crown-5-oxyacetic acid _1 exhibited high efficiency and selecvity in solvent extraction of alkali metal cations with respect to that observed with alkaline earth cations. Sizes of Na+ and Ca2+ appropriately match with the cavity size of monoethyl sym-bis[4(5)-tert-butylbenzo]-16-crown-5-oxymethylphosphonic acid _3. As the result, Na+ and Ca2+ are the best extracted. sym-(n-Octyldibenzo)-16-crown-5-oxymethyldiphosphonic acid _4was found to be somewhat selective for Na+ over Li+ and other alkaline earth metal cations. In the complexation of alklaine earth cations by crown ether diphosphonic acid _4, Ca2+ and Sr2+ are the appropriate sizes, but lager Ba2+ may be due to favorable formation of a sandwich type complex between the crown ether cavity and the dianion of the deprotonated crown ether phoaphonic acid moiety.

• 정연진 | Chung, Yeong-Jin