Selective iron-catalyzed aerobic oxidation of alcohols in water to carboxylic acids mediated by additives

Abstract

The direct catalytic oxidation of alcohols to carboxylic acids is very appealing, however, economic and environmentally friendly catalytic systems should be further explored from the aspect of less waste production and a convenient procedure. Herein, we display a structurally defined inorganic ligand-supported iron compound, (TBA)₃[FeMo₆O₁₈(OH)₆] (simplified as FeMo₆), which could be used as a heterogeneous molecular catalyst in water for this conversion, with oxygen as the terminal oxidant and KCl as an additive. The oxidation of various alcohols (aromatic and aliphatic) could be achieved in almost all cases under mild conditions and provided the corresponding carboxylic acids in high yields, including some active molecular entities and natural molecules with carboxyl structures. Detailed studies showed that chloride ions could combine with the molecular catalyst FeMo₆ to form a supramolecular aggregate FeMo₆·Cl, which could effectively catalyze the reaction, relying on the synergistic effect of chloride ions and FeMo₆. Control experiments, ¹H NMR studies and density functional theory (DFT) calculations showed that the oxidation reaction might involve a free radical pathway.