Highly efficient solvent extraction of water-soluble macrocyclic metal ligands, hydroxycalix[n]arene-p-sulfonates (n = 4, 6, 8) with trioctylmethylammonium chloride

Water-soluble hydroxycalix[n]arene-p-sulfonates, 1(n)(n-) (n = 4, 6, and 8) , were quantitatively extracted from an aqueous solution into chloroform wi th trioctylmethylammonium ion (TMA(+)) over a wide pH range. The extraction reaction of 1(n)(n-) with TMA(+)Cl(-) and the extraction constants were de termined from slope analyses of linearized extraction data and by the mole- ratio method. It was demonstrated that 1(n)(n-), having n moles of sulfonat o groups in an aqueous solution, could be extracted as 1(n) (TMA(+)), by as sociating with n moles of TMA(+) at a pH lower than that at which protonic dissociation of hydroxyl groups takes place, and that 1(n) (TMA(+))(n+j) wa s extracted at a pH higher than that for j moles of hydroxyl groups dissoci ate to form 1(n)((n+j)-). The extractability of 1(n)(n-) increased in the o rder of n (4 < 6 < 8); also, the pH range where complete extraction took pl ace became wider in the same order. As a possible application of the presen t extraction system, metal extraction with 1(4)(4-) was also shown for the purpose of selective separation of some metal ions.