Calix[4]arene dibenzocrown ethers as caesium selective extractants

A series of 1,3-dialkyloxycalix[4]arene dibenzocrown ethers were synthesized in the fixed 1,3-alternate conformation with good yields by the reaction of 1,3-dialkyloxycalix[4]arenes with dibenzodimesylate in the presence of caesium carbonate. The three dimensional 1,3-alternate conformation was confirmed by X-ray crystal structure. Upon two phase extraction, NMR studies on the ligand-metal complex, single ion and competitive ion transport experiments through a bulk liquid membrane, 1,3-dipropyloxycalix[4]arene dibenzocrown-6, in which two benzo groups are symmetrically attached to the crown-6 linkage, gave one of the most efficient and selective extractabilities for caesium ion over other alkali metal ions. From supported liquid membrane experiments using 1 and 3 as organic carriers, permeation coefficients of the caesium ion were estimated to be 0.42 and 0.27 cm h^-1, respectively. The selectivity of caesium over sodium ion was observed to increase with permeation time.