2-Pyridylmethyl-N-palmitoylglycine micelle-guided synthesis of a recyclable CuO@SiO2 nanocatalyst for hydride transfer nitro reduction in water

Abstract

Micelle-assisted syntheses have gained tremendous research interest owing to their ability to solubilize hydrophobic molecules within their core. Herein, we report the synthesis of CuO@SiO₂ core–shell nanoparticles using 2-pyridylmethyl-N-palmitoylglycine (PyN16G) micelles as a template. Removing the PyN16G template by calcination offered porous CuO@SiO₂ nanoparticles with a pore size of 1.44 nm. Transmission electron microscopy showed an irregular soft surface and core with a lattice fringe pattern, suggesting that the surface is porous SiO₂ and the core is made of crystalline CuO. The electronic properties of CuO@SiO₂ were revealed by X-ray photoelectron spectroscopy, and further, the elemental composition was confirmed by energy dispersive spectrometry. The CuO@SiO₂ was explored as a catalyst for hydride transfer reaction, where PyN16G micelles were used as a green medium to reduce lipophilic nitro compounds in water. The amino aromatics products were prepared from nitroaromatics in less than 15 min. The products are easily isolatable in good yield from the reaction medium without column chromatography. The catalyst was reused for more than 10 cycles in the hydride transfer reaction, and the micelles were reusable for three cycles. The reported hydride transfer reaction was tested on a large scale, where we demonstrated 1 g of nitro aniline conversion to diamino benzene in 15 min at 60 °C with good yield. The results imply that PyN16G micelles were an effective medium for producing porous nanomaterials and the synthesis of amino aromatics from nitroaromatic compounds bearing various functionalities.