Molecular Design of Organic Ligands with Highly Selective Recognition and Separation Function for Metal Ions

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Some 4-acyl-5-pyrazolone derivatives with bulky acyl substituent at 4-position have been prepared. The extraction of Sc (III) with smaller ionic radius decreased as the acyl group became bulkier. It is clear that the interligand contact in the Sc complex decreases the stability, since the pKa values of anthracenecarbonyl, acetyl, benzoyl and 3, 5-dimethylbenzoyl derivatives are very similar. The extraction of La (III) with larger ionic radius was governed by the electronic effect such as resonance effect by the substituents. The effect of the interligand contact and the distance between the two donating oxygens was seen in the extraction of tervalent Al. Ga and In.Novel 4-acyl-5-pyrazolones having the crown ether moiety as the intramolecular synergist have been synthesized and the solvent extraction of various metal ions has been examined. 4-Acyl-5-pyrazolone-substituted dibenzo-16-crown-5, dibenzo-19-crown-6, 12-crown-4, 15-crown-5 and 18-crown-6, and bis- (4-acyl-5-pyrazolone) -substituted diaza-18-crown-6 were designed and synthesized by facile coupling reactions. Alkali metal ions were readily extracted into chloroform. The selectivity was governed primarily by the crown ether moiety depending on the cavity size. Alkaline earth metal ions were also readily extracted into chloroform, however the selectivity is governed by both the acylpyrazolone and the crown ether moieties. Among the divalent transition metal ions, the extraordinarily high extractability was seen for Mn, Cd and Pb. It is well known that the extractability for these metal ions is much lower than the other divalent transition metal ions with the conventional chelating extractants. Such anomalous extraction was also given in the synergistic extraction with acylpyrazolone and crown ethers employed separately.