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

Abstract

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 8C 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.

Development of a General and Practical Iron Nitrate/TEMPO‐Catalyzed Aerobic Oxidation of Alcohols to Aldehydes/Ketones: Catalysis with Table Salt

“…In addition, we noticed in the very beginning that NaNO 3 and HNO 3 32 failed to replace Fe(NO 3 ) 3 in the recation of 3‐( n ‐hexyl)‐1,2‐octadien‐4‐ol, indicating the importance of Fe 3+ in the reaction (Scheme ).…”

Recent advances in green catalytic oxidations of alcohols in aqueous media

“…Similarly, Tong and coworkers [82] have reported highly efficient and selective aerobic oxidation of alcohols using a catalyst comprising TEMPO (1-3 mol%), ceric ammonium nitrate (5 mol%) and sodium nitrite (10 mol%), in water as solvent. The cheapest source of NO 2 is nitric acid and systems have been described [83][84][85] which utilize TEMPO/HNO 3 in the absence of added metals, i.e. transition metal-free systems.…”

Design and Synthesis of Hyperbranched Aromatic Polymers for Catalysis

“…For this purpose, a nitroxyl radical with low toxicity and reversible redox behavior, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), has been studied [37]. Furthermore, our research group presented a nitric acid–assisted carbon-catalyzed oxidation system (NACOS) using carbon-based materials as metal-free catalysts [38] and demonstrated that TEMPO enhanced this oxidation system [39]. Although TEMPO has typically been demonstrated as a homogenous catalyst, the immobilization of TEMPO onto solid supports such as polystyrene [40], silica [41], and iron oxide [42] has also been reported.…”

“…Two synthesized heterogeneous catalysts, TEMPO/HBPEK/CB and TEMPO/HBPEK/PI, exhibited a reliable catalytic activity. The performance of TEMPO/HBPEK/CB was slightly better than that of TEMPO/HBPEK/PI, perhaps due to the synergy between TEMPO and CB [39]. Both TEMPO/HBPEK/CB and TEMPO/HBPEK/PI were easy to separate from the reaction solution, and over 90 wt% of the catalysts were successfully collected by filtration.…”