Kinetics of Formation of the Monoacetylacetonato-Iron (III) Complex

Abstract

FEW kinetic investigations on the formation of complexes with β-diketones are found in the literature. Taft and Cook examined the reaction of thenoyltrifluoroacetone with various metal ions and in particular that with Fe(III). They found the rate-determining step is the reaction of Fe(III) with the enolate anion¹. Celiano and Gentile have investigated the kinetics of the reaction of acetylacetone, benzoylacetone and its derivatives with Cu(II), and indicated that the rate-determining step is the reaction of Cu(II) with the enol form of the β-diketone and with its enolate anion². In an attempt to evaluate the two types of mechanisms proposed, we have examined the reaction of acetylacetone, benzoylacetone, trifluoroacetyl-acetone and thenoyltrifluoroacetone with Fe(III)³. The behaviour is very similar in all cases and under our conditions the product is the mono-chelated complex, Fe(AA)²⁺. The results of experiments on the acetylacetone/Fe(III) reaction are reported here.