Hydroxylamine as a Source for Nitric Oxide in Metal‐Free 2,2,6,6‐ Tetramethylpiperidine N‐Oxyl Radical (TEMPO) Catalyzed Aerobic Oxidation of Alcohols

Abstract

The communication reports on the metal‐free 2,2,6,6‐tetramethylpiperidine N‐oxyl radical (TEMPO) catalyzed aerobic oxidation of various alcohols to aldehydes and ketones. A novel catalyst system that uses 1–4 mol% of TEMPO in combination with 4–6 mol% of aqueous hydroxylamine is introduced. No other additives are necessary and corrosive by‐products are not formed during oxidation. Nitric oxide which is important for the catalytic cycle is generated in situ by reaction of the hydroxylamine with TEMPO. A catalytic cycle for the overall oxidation process is suggested.

SBA‐15‐Functionalized 3‐Oxo‐ABNO as Recyclable Catalyst for Aerobic Oxidation of Alcohols under Metal‐Free Conditions

“…To address these problems, the application of stable nitroxyl radicals, especially 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its derivatives, has received a great deal of interest for the selective oxidation of alcohols under metal-free conditions using molecular oxygen as a terminal oxidant. [6] In this context, the use of non-transition metal co-catalysts such as tBuONO (TBN) [7] and NaNO 2 [8] is well documented for the oxidation of primary and secondary alcohols in the presence of TEMPO. However, many of these methods are inefficient when using aliphatic and secondary alcohols; therefore, their wide-spread applicability is hampered.…”

Aerobic Oxidations via Organocatalysis: A Mechanistic Perspective

“…Wertz and Studer also used aqueous NH2OH instead of NaNO2/HCl to provide the NOx source, and they confirmed the efficiency of this system for TEMPO catalyzed alcohol oxidation, which gives ketone products in yields of 87-97%, even 21% for cyclohexanone (Scheme 16). (42) In this neutral condition, the hydride-transfer mechanism might also be involved. Besides TEMPO, ABNO and AZADO also have lower NO-H bond BDE than that of NHPI, and the alcohol oxidations promoted by ABNO and AZADO are considered to be through their oxoammonium cations.…”

“…Wertz and Studer also used aqueous NH 2 OH instead of NaNO 2 /HCl to provide the NO x source, and they confirmed the efficiency of this system for the TEMPO-catalyzed oxidation of alcohols to give ketones of 87-97% yield, even 21% for cyclohexanone (Scheme 20). 42 Under these neutral conditions, the hydride-transfer mechanism might also be involved.…”

Übergangsmetallfreie oxidative Kreuzkupplung von Tetraarylboraten zu Biarylen mit organischen Oxidationsmitteln

“…[20] Seit 2004 wurden übergangsmetallfreie Varianten mit TEMPO als Katalysator, Stickstoffmonoxid als Co-Katalysator und molekularem Sauerstoff als terminalem Oxidans entwickelt. [21] Motiviert von diesen Berichten testeten wir unterschiedliche co-katalytische Systeme um das Oxoammoniumsalz in situ zu regenerieren.…”

“…Es wird angenommen, dass im Katalysezyklus in situ erzeugtes NO 2 das 4-AcNH-TEM-POBAr 2 zum entsprechenden Oxoammoniumsalz reoxidiert und selbst durch O 2 regeneriert wird. [21] Das Biaryl 5 t, das eine Estergruppe enthält, wurde in 46 % erhalten und das Chlor-substituierte Biaryl 5 u wurde ebenfalls erfolgreich hergestellt, wenn auch in geringerer Ausbeute. In beiden Fällen ist die niedrigere Ausbeute hauptsächlich auf eine verringerte Kreuzkupplungsselektivität zurückzuführen, die in der Bildung der von den "Dummyliganden" herrührenden Biaryl-Nebenprodukte resultierte.…”