Silica-Supported 4-OH-TEMPO/NO_x: A Novel and Efficient Catalyst for Aerobic Oxidation of Alcohols

Abstract

Silica-supported 4-OH-2,2,6,6-tetramethylpiperidyl-1-oxy/NO_x (4-OH-TEMPO was immobilized on the surface of silica using the sol-gel method, and then it adsorbed NO_x), as a heterogeneous catalyst, has exhibited good catalytic performance in alcohol oxidation. A broad range of alcohols were oxidized to their corresponding aldehydes or ketones with more than 99% selectivity and 99% conversion rate by such a catalyst system at room temperature in air. NO_x not only acted as an electron bridge between O₂ and 4-OH-TEMPO but also were conducive to the formation of the aldehydes as active component. A possible mechanism for oxidation of alcohols promoted by silica-supported 4-OH-TEMPO/NO_x was supposed.

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GRAPHICAL ABSTRACT

Keywords:

• Alcohol oxidation
• molecular oxygen
• NO_x
• sol-gel
• TEMPO

ACKNOWLEDGMENT

This work is partially supported by the Program for Changjiang Scholars and Innovative Research Team in University (IRT0711).

Notes

^a Quality percentage.

^b Silica-supported 4-OH-TEMPO/NO_x had been used five times.

^a Diameters of the pores are between 1.7000 and 300.0000 nm.

^b BJH adsorption average pore diameter (4 V/A).

^c Silica supported 4-OH-TEMPO has been used once.

^d Catalyst has been used five times.

^a Substrate (1 mmol), silica-supported 4-OH-TEMPO/NO_x (0.5 g), CH₂Cl₂ (6 mL), room temperature, and ambient pressure. Conversion and selectivity determined by GC.

^b No product was detected.