Extraction of cobalt(II) with mixtures of 4-acyl-pyrazol-5-ols and aliquat 336 in toluene: Effect of the pyrazolol substituents

Abstract

The extractions of cobalt(II) from 1M (Na, H)ClO4 medium with mixtures of 4-acylpyrazol-5-ols (HL) (17 species) and aliquat 336 in its perchlorate form (B+, ClO4−) in toluene, at 25°C, have been studied. They are described by the equilibrium: $$Co^{2 + } + 3\overline {HL} + \overline {(B^ + ,ClO_4 ^-- )} \rightleftarrows \overline {(B^ + ,CoL_3 ^-- )} + 3H^ + ClO_4 ^-- .$$ Its constant is partly determined by the anionic exchange equilibrium between\(\overline {(B^ + ,ClO_4 ^-- )} \) and\(\overline {(B^ + ,ClO_4 ^-- )} \), which is favoured when HL substitutents are electron-attractive. Lipophilic substituents on HL favour the cobalt extraction, but conflicting effects can occur owing, for example, to steric hindrance.