Nano-Fe 3 O 4 encapsulated-silica particles bearing sulfonic acid groups (Fe 3 O 4 @SiO 2 -OSO 3 H) has been used as an efficient and magnetically separable heterogeneous catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles by one-pot, four-component reaction of benzil, aromatic aldehydes, primary amines, and ammonium acetate under neat conditions. The effect of various reaction parameters, such as reaction temperature, catalyst loading and solvent effect, were studied. The desired products are obtained in relatively short reaction times with high yields. Importantly, the catalyst could be easily separated from the reaction mixture by a permanent magnet and reused for several times without the significant loss of its activity.

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