Abstract

Background: Supporting of choline chloride (CC):2urea as a deep eutectic solvent (DES) on nonomagnetite gives the core-shell of nanoFe3O4@CC:2urea which in DES coating inhibits the agglomeration of nanoFe3O4 and nanoFe3O4 facilitates reusability of DES. The ratio of nanoFe3O4 to DES in nanoFe3O4@CC:2urea was determined as 8:1. These synergic effects led to a high catalytic performance for nanoFe3O4@CC:2urea versus individual nanoFe3O4 or CC:2urea in synthesis of pyrazole derivatives by various synthetic strategies. Faster reactions with higher yields at room temperature occur with low loading of this recyclable hybrid catalyst.

Method: NanoFe3O4 and DESs were prepared by co-precipitation of FeCl3.6H2O and FeCl2.4H2O with NH3 and heating the mixture of CC and hydrogen donors to a homogeneous liquid. Then, nanoFe3O4@CC:2urea was prepared by sonication of nanoFe3O4 and dissolved CC:2urea in methanol. After characterization by FT-IR, SEM, TEM, TGA, and VSM, the efficacy of nanoFe3O4@CC:2urea was examined in one-pot synthesis of pyrazoles and pyranopyrazoles.

Results: NanoFe3O4@CC:2urea is a hybrid organic/inorganic catalyst which in DES coating inhibits the agglomeration of Fe3O4 nanoparticles and nanoFe3O4 improves the reusability of DES. These synergic effects deliver a high catalytic performance for nanoFe3O4@CC:2urea in synthesis of pyrazoles and pyranopyrazoles. Faster reactions with higher yields at room temperature occur with low loading of this magnetically separable and reusable catalyst.

Conclusion: In summary, synergic effects of CC:2urea and nanomagnetite in nanoFe3O4@CC:2urea lead to a reusable catalyst with superior catalytic activity in room temperature three- or four- component synthesis of pyrazoles and pyranopyrazoles. This magnetically separable DES provides higher yields of products, faster reactions, and milder conditions compared to previous reported methods.

Keywords: Deep eutectic, nanoFe3O4, immobilization, pyrazoles, multicomponent reactions, synergic effect.

Graphical Abstract