A Nitric Acid-Assisted Carbon-Catalyzed Oxidation System with Nitroxide Radical Cocatalysts as an Efficient and Green Protocol for Selective Aerobic Oxidation of Alcohols

The incorporation of nitroxide radicals into a nitric acid-assisted carbon-catalyzed oxidation system (NACOS) afforded a highly efficient, widely applicable, non-metallic approach for the selective aerobic oxidations of alcohols. Without any solvent, this novel protocol has the ability to oxidize various primary alcohols to their corresponding aldehydes with selectvities as high as 99% at full conversions, with only 0.1 mol% of nitroxide radicals and <4.5 wt% of activated carbon under mild conditions (temperatures as low as 50 degrees C and atmospheric pressure). The performances of several stable nitroxide radicals have been compared. The effects of nitric acid concentration, activated carbon loading, and temperature have been studied for the oxidation of benzyl alcohol. The enhanced NACOS represents a greener and more efficient fundamental chemical process, due to its use of molecular oxygen as an oxidant, and its solvent-free nature.