Utilization of eggshell waste as green catalyst for application in the synthesis of 1,2,4,5-tetra-substituted imidazole derivatives

Eggshell as a solid waste was loaded on a nano-Fe 3 O 4 surface. Then, in one step, it (Fe 3 O 4 @eggshell) was converted to Fe 3 O 4 @Ca 3 (PO 4 ) 2 as a nano-magnetic, green, cheap, and environmentally friendly catalyst. Techniques such as FT-IR, VSM, FESEM, TEM, EDX, XRD, and TGA were used to characterize the as-synthesized catalyst. The catalytic activity of Fe 3 O 4 @Ca 3 (PO 4 ) 2 was evaluated in the synthesis of 1,2,4,5-tetra-substituted imidazole derivatives through a one-pot multicomponent reaction. The design of the experiment as a systematic statistical approach was used to obtain the optimum point of the reaction condition so that 0.05 g of the as-synthesized catalyst and 94.77 °C were the best condition (which provides 90% yield for the benchmark reaction). Then, 1,2,4,5-tetra-substituted imidazole derivatives in the optimum condition were synthesized with very low reaction times in good yields. The as-prepared catalyst was retrieved through a magnet and used several times without significant loss of catalytic activity. Graphical abstract