An Efficient Aerobic Oxidation of Alcohols to Aldehydes and Ketones with TEMPO/Ceric Ammonium Nitrate as Catalysts
Sung Soo Kim*, Hyun Chul Jung
*Department of Chemistry and Center for Chemical Dynamics, Inha University,
Incheon 402-751, South Korea, Email: sungsoo
inha.ac.kr
S. S. Kim, H. C. Jung, Synthesis, 2003, 2135-2137.
DOI: 10.1055/s-2003-41065
Abstract
The combination of TEMPO and CAN can be used for the aerobic oxidation of benzylic and allylic alcohols into their corresponding carbonyl compounds. However, steric hindrance has been observed to impede the reaction with some substituted allylic systems. The present method is superior to others currently available due to its relatively short reaction times and excellent yields.
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simplified oxidation mechanism
Details
The document discusses an efficient method for the aerobic oxidation of alcohols to aldehydes and ketones using TEMPO (2,2,6,6-tetramethylpiperidinyloxyl) and ceric ammonium nitrate (CAN) as catalysts. The study, conducted by Sung Soo Kim and Hyun Chul Jung at Inha University, highlights that secondary benzylic alcohols with alkyl chains oxidize faster than simple benzyl alcohols, while those with bulky phenyl rings exhibit prolonged reaction times. The method achieves yields greater than 90% for benzylic and benzylic alcohols and over 80% for allylic alcohols without steric hindrance. The oxidation process is superior to existing methods due to its shorter reaction times and excellent yields.
The oxidation mechanism involves the reduction of dioxygen to water by the oxidation of Ce3+ to Ce4+, which then oxidizes TEMPO to an N-oxoammonium cation. This cation subsequently oxidizes the alcohol to the corresponding carbonyl compound. The study also includes control experiments to determine the role of each reagent, showing that both CAN and TEMPO are crucial for the reaction. The method is effective for a wide range of substrates, although steric hindrance can affect the reaction rate. The procedure involves dissolving the alcohol, CAN, and TEMPO in acetonitrile, heating under a stream of O2, and purifying the product via silica gel chromatography.
Key Words
air oxidation, TEMPO, cerium ammonium nitrate, benzylic alcohols, allylic alcohols, aldehydes, ketones, enones
ID: J66-Y2003-1570
