Solvent extraction is known to be a very effective and selective separation method for metal ions. [1][2][3][4] Acylpyrazolones are powerful chelating reagents, and have been used for the solvent extraction of metal ions. [5][6][7] In the solvent extraction of metal ions with chelating reagents, such as acylpyrazolones, the extractability mainly depends on the stability of the complex formation of the chelating reagent and the metal ion.Macrocyclic ligands, such as crown ethers and cryptands, have been utilized in metal-ion separations.
8Many novel macrocyclic ligands have been prepared as ion-pair extraction reagents, exhibiting excellent separation ability. 9 It was shown that water soluble macrocyclic ligands could enhance the separability when they were added in the aqueous phase as ionsize selective masking reagents in the extraction of alkali, alkaline earth and lanthanide metal ions with the chelate extraction reagents. 10,11 On the contrary, it is known that neutral macrocyclic ligands can work as synergists when they were added in the organic phase. In both cases, unique separability would be expected, since the selectivity of the macrocyclic ligands and the chelating reagents is quite different. In this regard, a reagent which has an acylpyrazolone unit and a crown ether unit in the same structure is expected to show unique selectivity. Although a large number of crown ethers bearing pendant groups have been synthesized, 12,13 only a few examples of crown ether-bearing chelating reagents have been reported. 14,15 In the present work, novel acylpyrazolones, HPMP-A15C5 and HPMP-A18C6 (Fig. 1) were prepared and the extractions of seven divalent metal ions (Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ and Pb 2+ ) were examined. The results were compared with those of the synergistic extractions using benzocrown ethers as synergistic reagents.
Experimental
Chemicals and apparatus1-Aza-15-crown-5, 1-aza-18-crown-6, benzo-15-crown-5 (B15C5) and benzo-18-crown-6 (B18C6) were purchased commercially from Tokyo Kasei, and 1-phenyl-3-methyl-4-chloroacetyl-5-pyrazolone was synthesized according to the literature. 16 Good's buffers were purchased commercially from Nacalai Tesque. Metal solutions were prepared from standard solutions provided by Wako. These were used without further purification. Other chemicals were of reagent-grade materials. Water was demineralized and distilled.The metal-ion concentrations were measured with a Japan Jarrell Ash Model ICAP-500 inductively coupled argon plasma atomic emission spectrophotometer. pH measurements were made with a Hitachi-Horiba F-8L pH meter equipped with Horiba 6028 glass combination pH electrode. The pH meter was calibrated against standard reference buffers. 1 H-NMR spectra were measured with a JEOL JNM-AL300 spectrometer Novel 4-acyl-5-pyrazolones having aza-15-crown-5 (HPMP-A15C5) and aza-18-crown-6 (HPMP-A18C6) moieties as an intramolecular synergist have been synthesized by simple coupling reactions between 1-phenyl-3-methyl-4-chloroacetyl-5-pyrazolone and the...
