ZnII doped and immobilized on functionalized magnetic hydrotalcite (Fe3O4/HT-SMTU-ZnII): a novel, green and magnetically recyclable bifunctional nanocatalyst for the one-pot multi-component synthesis of acridinediones under solvent-free conditions

Abstract

Zn^II doped and immobilized on functionalized magnetic hydrotalcite (Fe₃O₄/HT-SMTU-Zn^II) was prepared for the first time as a stable, long-lived, highly efficient and exceptional reusable magnetic nanocatalyst for the one-pot multi-component synthesis of acridinediones as an important class of heterocyclic compounds. The synthesized catalyst was characterized by various spectroscopic and microscopic techniques such as Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, Brunauer, Emmett and Teller (BET) surface area analysis, temperature programmed desorption (TPD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), inductively coupled plasma atomic emission spectroscopy (ICP-OES) and CHNS analysis. The results of characterizations showed the superparamagnetic nature of the catalyst with an average particle size of 20–60 nm which is plate-like in shape. Also, the results of the TPD analysis showed that the nanocatalyst has both acidic sites (site density: 22.66 mmol g⁻¹) and basic sites (site density: 8.49 mmol g⁻¹), and can act as a bifunctional nanocatalyst. The loading amount of Zn^II (doped and immobilized) on functionalized magnetic hydrotalcite was indicated to be 4 mmol g⁻¹, obtained from the ICP-OES analysis. The catalytic activity of this new magnetic nanocatalyst (Fe₃O₄/HT-SMTU-Zn^II) was examined in the multi-component reaction of aromatic aldehydes, dimedone, and various primary amines or NH₄⁺ under solvent-free conditions towards the preparation of acridinedione derivatives in a short period of time. In all the cases, the catalyst could be easily recovered magnetically for at least six runs and the obtained product was isolated using a simple work-up procedure. In our protocol, the solvent-free conditions avoid the problems such as cost, handling, safety and pollution which are related to solvent use. The characteristics of the present methodology make the reaction suitable for scale-up and commercialization.