The kinetics of formation of the mono(acetylacetonato)iron(III) complex

Abstract

The kinetics of the reactions between ferric ion and acetylacetone in aqueous solution have been studied. The rate equation when ferric ion is present in excess is: Rate =k₁[Haca]+k₂[Haca][Fe]+k₃[Haca][Fe]/[H⁺]. The effect of variation of temperature and ionic strength have also been examined. The simplest interpretation of the data is that formation of the complex in the range of acidities studied takes place by three routes: (i) the slow formation of the anion of the ligand followed by rapid reaction of it with ferric ion; (ii) the reaction of neutral acetylacetone molecule with a ferric ion or of a protonated acetylacetone molecule with the hydroxo-species Fe(OH)²⁺; (iii) the reaction of a neutral acetylacetone molecule with the Fe(OH)²⁺ species.