Synergistic extraction of alkaline earth cations with 3-phenyl-4-benzoyl-isoxazol-5-one and tri-n-octylphosphine oxide in toluene

The synergistic extraction of alkaline earth cations from 1M NaNO3, aqueous solutions with 3-phenyl-4-benzoylisoxazol-5-one (HPBI) and tri-n-octylphosphine oxide (TOPO) in toluene at 25 degrees C has been studied. The extraction efficiency follows the order Ba2+ < Sr2+ < Ca2+ < Mg2+, which is the same as that previously observed with 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (HPMBP). The extraction occurs at a lower pH range than with HPMBP because of the higher acidity of HPBI. The extracted species are M(PBI)(2)(TOPO)(x) with x=2 for M=Mg, Ca, Sr and Ba (log K-1,K-2,K-2 = 3.91, 3.69, 1.18 and 0.29 respectively) and with x = 3 for M = Sr and Be (log K-1,K-2,K-3 = 3.28 and 2.07 respectively). M2+ + 2 HPBIorg + x TOPOorg reversible arrow(K,1,2,x) M(PBI)(2)(TOPO)(x,org) + 2 H+ The strong interactions which occur between HPBI and TOPO (log K-int = 1.84) have been considered in the extraction constant calculations. HPBIorg + TOPOorg reversible arrow(Kint) TOPO . HPBIorg.