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, 1nn− (n = 4, 6, and 8), were quantitatively extracted from an aqueous solution into chloroform with trioctylmethylammonium ion (TMA+) over a wide pH range. The extraction reaction of 1nn− with TMA+Cl− and the extraction constants were determined from slope analyses of linearized extraction data and by the mole-ratio method. It was demonstrated that 1nn−, having n moles of sulfonato groups in an aqueous solution, could be extracted as 1n (TMA+)n by associating with n moles of TMA+ at a pH lower than that at which protonic dissociation of hydroxyl groups takes place, and that 1n (TMA+)(n+j) was extracted at a pH higher than that for j moles of hydroxyl groups dissociate to form 1n(n+j)−. The extractability of 1nn− increased in the order of n (4 < 6 < 8); also, the pH range where complete extraction took place became wider in the same order. As a possible application of the present extraction system, metal extraction with 144− was also shown for the purpose of selective separation of some metal ions.