Dipyridinium-Type Anion-Exchange Extractants for Anionic Metal Complexes and Disulfonate Anions

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Abstract
A new series of anion-exchange extractants, polymethylenebis[3-(N, N-dioctylcarbamoyl)pyridinium]s (abbreviated as CnBPy; n=3, 4, 6, 8, 10) were synthesized; they are lipophilic dipyridinium ions bearing two cationic centers at various separations within a molecule. The extraction behavior of metal ions from aqueous hydrohalic acid was investigated. The extractability of divalent metal ions (zinc(II) and cadmium(II)) decreased in the order: C10->C8- >C6->C4->C3BPy> monocationic extractant (1-butyl-3-(N, N-dioctylcarbamoyl)pyridinium, abbreviated as BuMPy). However, in the extraction of trivalent metal ions ( iron(III) and indium(III)), the extraction ability of extractants decreased in the order: BuMPy_??_C10->C8->C6->C4->C3BPy. These orders were analogous to those observed in the previously reported extractions using diphosphonium extractants. The extraction of organic dianionic substrates, 1, 5- and 2, 6-naphthalenedisulfonates (abbreviated as NDS2-) was also investigated. The extraction of 1, 5-NDS2- decreased in the order: C10_??_C8-_??_C6->C4->C3BPy, while that of 2, 6-NDS2-decreased in the order: C10- >C8->C6->C4->C3BPy. There were no distinct maxima in the plot of extraction constant (log Kex) vs. n-value; such behavior was considerably different from that of diphosphonium extractants reported previously. The structural aspects of extractants and their relation to extraction selectivity are discussed.