Bleach Catalysis in Aqueous Medium by Iron(III)-Isoindoline Complexes and Hydrogen Peroxide

Abstract

Hydrogen peroxide and peroxymonocarbonate anion based bleach reactions are important for many applications such as paper bleach, waste water treatment and laundry. Nonheme iron(III) complexes, [FeIII(L1-4)Cl2] with the 1,3-bis(2’-Ar-imino)isoindolines ligands (HLn, n = 1-4, Ar = pyridyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl, respectively) have been shown to catalyze the oxidative degradation of morin as a soluble model of a bleachable stain by H2O2 in buffered aqueous solution. In these experiments the bleaching activity of the catalysts was significantly influenced by the Lewis acidity and redox properties of the metal centers, and showed a linear correlation with the FeIII/FeII redox potentials (in the range of 197 to 415 mV) controlled by the modification of the electron donor properties of the ligand introducing various aryl groups on the bis-iminoisoindoline moiety. Similar trend but with low yields was observed for the disproportionation of H2O2 (catalase-like reaction) which is a major side reaction of catalytic bleach with transition metal complexes. The effect of bicarbonate ions might be explained by the reduction of Fe(III) ions and/or the formation of peroxymonocarbonate monoanion, which is much stronger oxidant and could increase the formation of the catalytically active high-valent oxoiron species.