Terpyridine-manganese complexes: A new class of bleach catalysts for detergent applications

Abstract

Oxidation catalysis is one approach used to improve the performance of hydrogen peroxide in laundry bleach applications. We introduce herein a new class of bleach catalysts based on the ligand 2,2′∶6′,2″ terpyridine. A set of manganese complexes of substituted terpyridines was investigated with respect to their physicochemical properties and bleach performance. Introduction of electron-donating hydroxy and amine substituents in the 4-position of the individual pyridine rings improves the bleach performance in model experiments with morin (2′,3,4′,5,7-pentahydroxyflavone) in solution as well as on tea-stained cotton fabrics. All the catalysts show excellent bleach performance at 40 and 25°C under European washing conditions. Performance is superior to that of the activator tetraacetyl ethylenediamine (TAED) but depends critically on the substitution pattern. Dye damage caused by the catalysts is similar to that of TAED, proving that catalytic bleach systems with high performance and low damage are indeed feasible. Model experiments revealed that the complexes are highly stable under aqueous alkaline conditions in the presence of hydrogen peroxide. The optimal pH for catalytic activity is about 10. For a catalyst to have a high bleach performance, it must possess a sufficiently low activity to catalyze disproportionation of hydrogen peroxide, which is a major side reaction of catalytic bleach with manganese complexes. All the catalysts showed a similar affinity for the cotton fabric, suggesting that differences in bleach activity of complexes are not caused by differences in the fabric affinity.