A new type of water-soluble crown ether (3′-sulfobenzo-12-crown-4 (SB12C4), 3′-sulfobenzo-15-crown-5 (SB15C5), 3′-sulfobenzo-18-crown-6 (SB18C6), di(3′-sulfo)dibenzo-18-crown-6 (DSDB18C6), di(3′-sulfo)dibenzo-21-crown-7 (DSDB21C7), and di(3′-sulfo)dibenzo-24-crown-8 (DSDB24C8)) has been prepared. The complex formation constants (β) of lanthanide ions with sulfonated crown ethers in aqueous solution were determined via the solvent-extraction method. The stability of the resulting complexes increases with the number of sulfonic acid groups, 18C6 < SB18C6 < DSDB18C6. For mono and disulfonated crown ether complexes, the stability varies as SB18C6 < SB15C5 < SB12C4 and DSDB18C6 < DSDB21C7 < DSDB24C8. The β values of all the complexes of lanthanide ions decrease with the atomic number, which is a characteristic of macrocyclic ligands, and is quite opposite to the conventional complexing tendency. The extractive separability of lanthanide ions was found to improve by adding sulfonated crown ethers into the aqueous phase as ion-size selective masking reagents. The number of water molecules in the first coordination sphere of the central Eu3+ in the complex was determined by a laser-induced luminescence study. In addition, the fluorescence spectra were measured in order to evaluate the structure of the complexes. The stabilization of the complexes formed is discussed while taking into account an outer-sphere electrostatic attraction between the sulfonic acid group and the metal ion.
A water-solu ble macrocyclic compound, 4'-sulfobenzo-18-crown-6 (SBlSC6), was prepared and utilized as an ion size-selective masking reagent with a view to establishing a highly selective extraction-separation system. In the synergistic extraction of alkaline earths with 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone and trioctylphosphine oxide in cyclohexane or benzene, the extraction of those with larger ionic radii shifted to a higher pH region when SB18C6 was added to the aqueous phase, giving improved separations. A similar result was achieved in the extraction of lanthanides into chloroform with bis(2-ethylhexy1)phosphoric acid. The distribution of SB18C6 into cyclohexane, benzene or chloroform was so low in comparison with that of 18-crown-6 (18C6) and cryptand[2.2.2] that the synergistic extraction with 18C6, which usually reduces the selectivity, was not observed.
This investigation looked at the separation of divalent metal ions,
The 4,4,4-trifluoro-1-(2-thienyl)-1,3-butadione (TTA) used in to toluene solvent-extraction (SE) technique is known to be one of the most effective methods to remove or separate toxic metal ions. 1 We have developed a new solvent-extraction method to efficiently remove metal ions using an octadecyl silica gel (C18g) together with TTA (SE-C18g).2 This method showed an increase in the extraction ability of the metal ions compared with SE. The extraction mechanism of this system involves to adsorption of the extracted metal chelate in the organic phase onto C18g. 3 Because the adsorption reaction is affected by the affinity of C18g to the solvent, it is necessary to use a lower polarity organic solvent, such as toluene. A system has been developed that has no organic solvent, by retaining the TTA molecule directly onto C18g (TTA-C18g). However, the new TTA-C18g particles were found to aggregate together in the aqueous solution due to their hydrophobicity. Hence, a quantitative analysis of metal ion adsorption could not be performed. To prevent aggregation, the C18g particle size was increased. Larger TTA-C18g particles are less likely to aggregate, and are considered to have better adsorption ability. This paper reports on a new method to remove and separate metal ions, without the use of organic solvents, by using large TTA-C18g particles. Experimental Reagents and apparatusThe starting materials were silica gel (Wako Pure Chemical Industries, 1 -2 mm particle size) and TTA (Dojindo Laboratories). All other reagents were of analytical grade. Deionized water was prepared by a MilliQ Gradient A10 MILLIPORE and used throughout. An inductively coupled argon-plasma atomic emission spectrometry (ICP-AES, VARIAN VISTA-PRO) apparatus was used to determine to metal ion concentration in aqueous solution. The pH values of aqueous solutions were measured by a pH meter (HORIBA F-21) equipped with a glass electrode. Preparation of TTA-C18gSilica gel was crushed and sieved to a size of 0.50 -1.0 mm. The C18g was synthesized according to a published method. 4 In order to synthesize TTA-C18g, 50 cm 3 of toluene containing 0.5 mol dm -3 TTA was added to 10 g of C18g. After standing for 24 h at 277 K, the mixed solution was filtered, washed with deionized water and dried at room temperature under a vacuum. Adsorption experiment of divalent transition metal ionsAqueous solutions were prepared containing 1.0 × 10 -4 mol dm -3 metal ions (Co 2+ , Ni 2+ or Cu 2+ ), 0.1 mol dm -3 sodium perchlorate and 2.0 × 10 -2 mol dm -3 of a buffer agent (chloroacetic acid or acetic acid). A 20 cm 3 aliquot of each solution, along with 0.3 g of TTA-C18g, was put into a 50 cm 3 stoppered glass tube. In the case of Co 2+ , to prevent to oxidation of Co 2+ to Co 3+ , 1.0 × 10 -2 mol dm -3 ascorbic acid was added to the solution as a reductant. The stoppered glass tubes were shaken a few times each day to reach to reaction equilibrium (within 36 h) at 298 K. After the reaction was complete, the mixed solutions were filtered. The concentration of metal io...
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