CeO2 has been an important redox promoter in automotive catalysis, but limited studies have reported organic reactions by pore CeO2. This presentation summarizes our recent findings on CeO2-catalyzed green organic transformations of nitriles, amides and esters using various nucleophiles (H2O, alcohols, and amines). First, we found CeO2-catalyzed hydration of nitriles at low temperatures (eqn. 1) in water. Use of alcohols (eqn. 2) or amines (eqn. 3) as nucleophiles instead of H2O can lead to a design of CeO2-catalyzed one-pot esterification or N-alkyl amidation of nitrile under solvent-free conditions. Among various metal oxides, CeO2 shows the highest activity for (1) hydration of nitriles to amides in water, (2) one-pot ester synthesis from nitriles and alcohols, (3) one-pot synthesis of N-alkyl amide from nitriles with amines, and (4) synthesis of N-alkyl amide from amides and amines (transamidation). Also, CeO2 catalyzed the esterification of primary amides with alcohols under neutral conditions, providing the first versatile catalytic system for direct alcoholysis of amides to esters (eqn. 5). CeO2 acted as an efficient and reusable heterogeneous catalyst for transesterification of various esters with alcohols under the solvent-free conditions (eqn. 6). These methods are applicable in the synthesis of various amides, esters, and alkylamides in good to high yield (70-99%). For these reactions, the catalyst was easily retrieved from the reaction mixture by centrifugation and the recovered catalyst was reused at least three times without marked loss of its catalytic activity. Mechanistic studies suggest that the unique catalytic feature of CeO2 is due to the cooperation of Lewis acid site (Ce cation) and acid-base (Ce-O) pair site which activates an electrophile and a nucleophile, respectively.

Ceria-catalyzed transformations of amides, esters, and nitriles

2019 Fall National Meeting

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