Highly Effective Extraction of Iron(III) with 4-Isopropyltropolone in Nonpolar Solvents Containing 3,5-Dichlorophenol as a Synergist

A great enhancement in the extraction of iron(III) with 4-isopropyltropolone (Hipt) has been observed upon the addition of 3,5-dichlorophenol (DCP) as a hydrogen-bond donor, and highly efficient synergistic extraction system for iron(III) was presented using nonpolar solvents such as heptane and cyclohexane. An equilibrium study of the heptane system has demonstrated the formation of the adduct complexes of not only the iron(III) chelate, Fe(ipt)3·nDCP (n = 1 - 3), but the reagent, Hipt·nDCP (n = 1, 2). The formation constants (βM,n = [Fe(ipt)3·nDCP]org/[Fe(ipt)3]org[DCP]orgn, βH,n = [Hipt·nDCP]org/[Hipt]org[DCP]orgn) of the corresponding complexes were determined and evaluated by comparing with those of acetylacetone (Hacac). The values obtained for Fe(ipt)3 and Hipt were larger than those for Fe(acac)3 and Hacac, respectively, suggesting the higher hydrogen-bond accepting power and basicity of the former ligand.