Cross-linked polystyrene/titanium tetrachloride as a tightly bound complex catalyzed the modified Mannich reaction for the synthesis of piperidin-4-ones

Abstract

Cross-linked polystyrene beads were prepared, characterized and the resulting polymer carrier was functionalized with titanium tetrachloride (TiCl4) via complexation of polystyrene with TiCl4 to afford the corresponding cross-linked polystyrene-TiCl4 stable complex (PSt/TiCl4) in an one step reaction and characterized by FT-IR, UV, TGA, DSC, XRD, SEM, BET. This tightly bound coordination complex was used as a water tolerant, heterogeneous, recoverable and reusable Lewis acid catalyst for the synthesis of substituted piperidin-4-ones via the modified Mannich multi-component condensation of ketones, aromatic aldehydes, and ammonium acetate in 1:2:1 M ratio under mild conditions. The rate of reactions was found to decrease with an increasing percentage of crosslinking and the mesh size of the copolymer beads. The catalyst is water tolerant, stable and can be easily recovered and reused at least four times without any loss of activity.