Sulfonic Acid-Functionalized Ionic Liquids as Metal-Free, Efficient and Reusable Catalysts for Direct Amination of Alcohols

A series of sulfonic acid-functionalized (SO3H-functionalized) ionic liquids was synthesized and used as metal-free, highly selective and efficient catalysts for the direct amination of alcohols. Notably, the activities of the series of SO3H-functionalized ionic liquids were compared and a 92% isolated yield was obtained using 3-tetradecyl-1-(butyl-4- sulfonyl)imidazolium trifluoromethanesulfonate ([BsTdIM][OTf]) as the catalyst. Importantly, the catalytic system has wide substrate scope including benzylic, allyl, propargylic, aliphatic alcohols with sulfonamide, amide, carbamate, aromatic amine and N-heterocyclic compounds. Interestingly, the system was also suitable for a multi-gram scale direct amination of alcohols. Additionally, the reusable nature of [BsTdIM][OTf] makes this protocol more attractive and avoids the disposal and neutralization of acidic catalysts. Moreover, preliminary experiments indicated that this reaction should proceed via an SN1 pathway.