Alkali metal cation-anchored hydrated hydroxide complexes at the nanoscale interface as catalytic active sites for selective liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde

Abstract

Although water and alkali species synergistically activate C–H bonds and O₂ molecules in alcohol selective oxidation, the chemical states of these species and their regulatory mechanisms of the reaction pathways remain poorly understood. Herein, we report that alkali metal hydroxides alone act as efficient catalysts for the selective oxidation of benzyl alcohol to benzaldehyde under aqueous conditions. The catalytic efficiency is profoundly governed by the microstructural interplay at the biphasic interface, which is delicately modulated by parameters including the type and dosage of base, water content, alkali cation identity, and solvent polarity. Through isotopic labeling experiments and advanced spectroscopic analyses—including UV-vis absorption, fluorescence spectroscopy, and ¹H NMR—we identify the active catalytic site as a hydrated hydroxide complex anchored by alkali metal cations at the biphasic nanoheterogeneous interface. Notably, smaller alkali metal cations exhibit stronger water-binding affinity, which paradoxically reduces the reactivity for benzaldehyde formation. This counterintuitive behavior is attributed to metastable interfacial states that favor substrate and O₂ activation, thereby accelerating electron transfer and reaction kinetics. Our findings reveal that these complexes generate surface electronic states (SESs) through spatial orbital overlap between O atoms in H₂O and OH⁻, enabling concerted electron–proton transfer. This work not only clarifies the pivotal role of hydrated hydroxide complexes in selective alcohol oxidation, but also provides new insights into the design of metal-free catalytic systems for sustainable chemical synthesis.