Synergistic catalysis within core-shell FeO@SiO functionalized with triethylene glycol (TEG)-imidazolium ionic liquid and tetramethylpiperidine N-oxyl (TEMPO) boosting selective aerobic oxidation of alcohols.

HYPOTHESIS

It is expected that incorporation of 2, 2, 6, 6-tetra-methyl piperidine-N-oxyl radical (TEMPO) and an imidazolium bromide bearing hydrophilic triethylene glycol (TEG) groups on FeO@SiO core-shell may not only result in a novel highly water-dispersible/magnetically separable multi-functional catalyst system for metal-free aerobic oxidation of alcohols, which operates through a synergistic relay pathway, but it could potentially provide a strong platform for simultaneous separation and recycling of all components.

EXPERIMENTS

The catalyst was prepared by anchoring TEMPO moieties onto a magnetic core-shell FeO@SiO functionalized with an ionic liquid bearing TEG groups. The materials was characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption isotherms, thermal gravimetric analysis, and elemental analysis. The performance of the catalyst was evaluated and quantitatively measured in the aerobic oxidation of alcohols in water.

FINDINGS

The catalyst exhibited excellent and stable colloidal dispersion in water and high performance in the aerobic oxidation of various types of alcohols under metal- and halogen-free reaction conditions. As hypothesized, strong synergistic effect between functionalized components was seen in the described reaction. The catalyst displayed excellent dual-adjustable-selectivity in the oxidation of primary alcohols to either the corresponding aldehydes or carboxylic acids by tuning the reaction solvent and/or reaction time and excellent recycling behavior through a "double-separation-strategy".