Synergism of Metal and Organocatalysis in Condensation Reactions of Aromatic Aldehydes with Anilines Affording Imines: Effect of Catalysts on the Base of a Supported Cerium(III) and Proline

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Condensation reactions between 4-X-benzaldehydes (X = NO2, H, OCH3) and 4-Y-anilines (X = NO2, H, OCH3) catalyzed by new catalyst, i.e. Ce (III) supported on weakly acidic cation-exchanger resin of polyacrylate type and/or by proline as organocatalyst giving 4-Y-N-[(E)-(4-X-phenyl)methylidene]anilines, were studied. It was found that the both of the used catalysts, i.e. metal and organocatalyst, shortened reaction time, thus contributing to higher yields of products. The synergism between catalytic action of polymer supported Ce (III) and proline was found. It was observed that simultaneous application of metal and organocatalyst led to shorter reaction times. On the other hand, it was found that the synergic efficiency of the both applied catalysts depends on electron influence of the substituents X, Y present in 4-X-benzaldehyde and 4-Y-aniline, as well. Imines were prepared under catalysis by Ce (III), proline or by simultaneous use of both catalysts in the yields 97-99% and identified. For comparison, the above mentioned condensation reactions were carried out under classical catalysis by mineral acid with different, usually poor, results.