Abstract
In this work, an efficient method for the immobilization of L-proline on magnetic nanoparticles was offered and evaluated as a recoverable magnetic nanocatalyst for synthesis of 2,4,6-triarylpyridines through one-pot three-component reaction of acetophenone, aryl aldehydes and ammonium acetate. This article is the first report of the catalytic application of L-proline functionalized magnetic nanoparticles in organic reactions as a magnetic nanocatalyst. This novel magnetic nanocatalyst proved to be effective and provided the products in high to excellent yield under solvent-free conditions. The structure of obtained nanoparticles was characterized by Fourier transform infrared spectrophotometry (FT-IR), field-emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA) and energy-dispersive X-ray spectroscopy (EDX). TGA result revealed that it is stable up to 200 °C for using as a catalyst in organic reactions. FE-SEM image of the synthesized nanocatalyst showed that it has nearly core-shell spherical shape and uniform size distribution with an average size about 80 nm. Moreover, the catalyst could be easily recovered by facile separation by magnetic forces and recycled for several times without significant loss of its catalytic activity. The benefits of this study are simplicity, nontoxicity, low cost, simple workup, and an environmentally benign nature.
Highlights
In the recent years, organocatalysts have attracted increasing interest in organic synthesis from the green chemistry points of view[1,2,3,4]
In continuation of our research on the introduction of recoverable catalysts in organic synthesis[61,62,63], we report a convenient and facile one pot synthesis of 2,4,6- triarylpyridines from acetophenones 1 (2 mmol), aromatic aldehydes 2 (1 mmol) and NH4OAc 3 (1.5 mmol) in the presence of Fe3O4\SiO2\propyltriethoxysilane\L-proline nanoparticles (LPSF) nanoparticle, as heterogeneous catalyst at 60 °C under solvent-free conditions (Fig. 1)
L-proline N-hydroxysuccinimide ester was prepared from L-proline and N-hydroxy succinimide (NHS) in the presence of N,N’-dicyclohexylcarbodiimide (DCC)
Summary
We have synthesized a novel nanomagnetic organocatalyst Fe3O4\SiO2\propyltriethoxysilane\L-proline (LPSF) and applied for the synthesis of 2,4,6-triarylpyridines. The synthesize Fe3O4\SiO2\3-aminopropyltriethoxysilane was treated by NHS-L-proline to synthesize the aimed LPSF magnetic nanocatalyst. In order to investigate the possibility of several recycling runs for LPSF magnetic nanocatalyst, the solid catalyst was separated from the reaction mixture by using an external magnet. It was washed two times with ethanol and water, dried and reused in subsequent reactions. After completion of the reaction, the products were separated by an external magnet and washed several times with ethanol. A mixture of acetophenones (2 mmol), aromatic aldehyde (1.0 mmol), ammonium acetate (1.5 mmol) and 0.01 g LPSF nanocatalyst was stirred at 60 °C under solvent-free conditions for an appropriate time.
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