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TEMPO and Carboxylic Acid Functionalized Imidazolium Salts/Sodium Nitrite: An Efficient, Reusable, Transition Metal‐Free Catalytic System for Aerobic Oxidation of Alcohols
Author(s) -
Miao ChengXia,
He LiangNian,
Wang JinQuan,
Wang JingLun
Publication year - 2009
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.200900285
Subject(s) - chemistry , alcohol oxidation , catalysis , aldehyde , alcohol , ionic liquid , transition metal , ketone , allylic rearrangement , carboxylic acid , organic chemistry , hydrogen bromide , bromide , sodium nitrite , inorganic chemistry , bromine
An effective catalytic system comprising a 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) functionalized imidazolium salt ([Imim‐TEMPO] + X − ), a carboxylic acid substituted imidazolium salt ([Imim‐COOH] + X − ), and sodium nitrite (NaNO 2 ) was developed for the aerobic oxidation of aliphatic, allylic, heterocyclic and benzylic alcohols to the respective carbonyl compounds with excellent selectivity up to >99%, even at ambient conditions. Notably, the catalyst system could preferentially oxidize a primary alcohol to the aldehyde rather than a secondary alcohol to the ketone. Moreover, the reaction rate is greatly enhanced when a proper amount of water is present. And a high turnover number (TON 5000) is achieved in the present transition metal‐free aerobic catalytic system. Additionally, the functionalized imidazolium salts are successfully reused at least four times. This process thus represents a greener pathway for the aerobic oxidation of alcohols into carbonyl compounds by using the present task‐specific ionic liquids in place of the toxic and volatile additive, such as hydrogen bromide, bromine, or hydrogen chloride (HBr, Br 2 or HCl), which is commonly required for the transition metal‐free aerobic oxidation of alcohols.