EXTRACTION OF COBALT(II) WITH MIXTURES OF 4-ACYL-PYRAZOL-5-OLS AND ALIQUAT-336 IN TOLUENE - EFFECT OF THE PYRAZOLOL SUBSTITUENTS

The extractions of cobalt(II) from 1 M (Na, H)ClO4 medium with mixtures of 4-acyl-pyrazol-5-ols (HL) (17 species) and aliquat 336 in its perchlorate form (B+, ClO4-) in toluene, at 25-degrees-C, have been studied. They are described by the equilibrium: Co2+ + 3 HLBAR + (B+, ClO4-)BAR reversible (B+, CoL3-)BAR + 3 H+ + ClO4-. Its constant is partly determined by the anionic exchange equilibrium between (B+, ClO4-)BAR and HLBAR, which is favoured when HL substituents are electron-attractive. Lipophilic substituents on HL favour the cobalt extraction, but conflicting effects can occur owing, for example, to steric hindrance.