The solvent extraction of iron(III) from chloride solutions by N,N′-tetrasubstituted malonamides:: Structure-activity relationships

The extraction of iron( III) from chloride solutions has been investigated using N,N'-dimethyl-N,N'-diphenylhexylmalonamide (DMD Phi(H)MA), N,N'-dimethyl- N,N'-diphenyldodecylmalonamide (DMD Phi(D)MA), N,N'-dimethyl-N,N'-dicyclohexylmalonamide (DMDCMA) and N,N'-dimethyl- N,N'-dihexylmalonamide (DMDHMA). The main aim of this work was to investigate whether there is a relation between the chemical structure of malonamides and their iron( III) extraction behavior, and to try to understand the dependence of the metal extraction mechanism on the structural characteristics of the malonamides. The introduction of an alkyl chain on the central carbon atom of N,N'-dimethyl-N,N'-diphenyl skeleton malonamides increases the affinity of the organic derivatives for iron(III) at lower hydrochloric acid concentrations: the longer the alkyl chain, the lower the acidity of half of the extraction of iron(III) is. A similar behavior has been observed both for DMDCMA and DMDHMA when N,N'-dimethyl-N,N'-diphenylmalonamide (DMDFMA) is taken as a reference. The collected spectroscopic results point out that either the presence of a central alkyl chain on N,N'-dimethyl-N,N'-diphenyl skeleton malonamides or the replacement of the N,N'-diphenyl groups by dicyclohexyl-or di-n-hexyl ones, likely determines iron(III) extraction through a solvation pathway, also involving the extraction of HCl molecules.