Boosting Peroxide Reactivity: New Mn(II) Chelidamate Catalysts for Efficient Low-Temperature Bleaching

Abstract

The development of efficient catalytic systems for low-temperature bleaching is a key challenge for reducing energy consumption in laundry processes. In this work, five manganese(II) complexes derived from chelidamic acid were designed, synthesized, and evaluated as bleaching catalysts for the activation of hydrogen peroxide under mild and aqueous conditions. The ligand framework was functionalized by O-alkylation at the 4-hydroxy group with neutral, cationic, and anionic substituents to modulate hydrophobicity and charge distribution. All complexes were tested in morin bleaching as a benchmark reaction, exhibiting good conversions (>90%) already at 20 °C within a short reaction time (30 min). The O-functionalized Mn(II) complexes significantly outperformed the free hydroxyl analogue and Mn(II) salt precursor. Kinetic analysis revealed the presence of an induction period, followed by a quasi-linear regime used to determine apparent turnover frequencies (TOF), ranging from ∼80 to 180 h–1. The catalytic behavior was strongly influenced by the reaction medium, showing a marked dependence on bicarbonate buffer concentration, achieving optimal activity at moderate alkaline pH (≈9.3). Notably, efficient bleaching was achieved at low catalyst concentrations (μM range) and low hydrogen peroxide loadings (0.05% w/w). Furthermore, the catalytic system was also effective in the oxidation of the azo dye Sunset Yellow FCF, supporting its potential application in the wastewater treatment of degradation-resistant pollutants. These results highlight the importance of ligand design in tuning catalytic performance and support the potential application of these manganese complexes as sustainable bleaching catalysts operating under mild conditions.