Abstract
A series of liquid anion-exchange extractants R3P+-Y-P+R3, polymethylenebis(trioctytphosphonium)s (Y=(CH2)n, n=2, 3, 4, 6, 10) and xylylenebis(trioctylphosphonium)s (Y=o-, m-, p-xylylene), were synthesized. These are lipophilic diphosphonium ions bearing two cationic centers at various distances within a molecule. The extraction of organic sulfonate anions, α-naphthalenesulfonate (NS-) as well as 1, 5- and 2, 6-naphthalenedisulfonates (NDS2-) was investigated by using these extractants. From equilibrium studies, the monoanionic sulfonate (NS-) was found to be extracted via the stepwise formation of 1:1 and 1: 2 ion pairs, while the dianionic sulfonates (1, 5- and 2, 6-NDS2-) formed 1:1 ion pairs for all of the diphosphonium extractants. The extractability of NDS2- exhibited a remarkable dependence on the distance separating two ionic centers in the dicationic extractants as well as in NDS2-. The extraction of NS- did not show such an effect. A mechanism is discussed for the recognition of interionic distance in the extraction of di-ionic substrates.
