Abstract
Chitosan microspheres modified by 2-pyridinecarboxaldehyde were prepared and used in the construction of a heterogeneous catalyst loaded with nano-Cu prepared by a reduction reaction. The chemical structure of the catalyst was investigated by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and X-ray Photoelectron Spectroscopy (XPS). Under mild conditions, such as no ligand at room temperature, the catalyst was successfully applied to catalyze the borylation of α,β-unsaturated receptors in a water-methanol medium, yielding 17%–100% of the corresponding β-hydroxy product. Even after repeated use five times, the catalyst still exhibited excellent catalytic activity.
Highlights
The development of heterogeneous catalysts has become a core approach to green, sustainable chemistry due to their ease of recycling, reusability, and environmental friendliness in comparison to homogenous catalysts [1,2]
Themodified morphology and diameter of the modified chitosan microspheres are shown in Figure chitosan by 2-Pyridinecarboxaldehyde was mostly spherical, and the diameter of the particles
Α,β,γ,δ-dienone substrates (4z) successfully gave the 1,4-addition product (6z) with a low yield of 17%. These results demonstrated that the modified chitosan catalyst supported copper (CBS@Cu0) in a heterogeneous catalyst, with an excellent catalytic performance in the boron addition
Summary
The development of heterogeneous catalysts has become a core approach to green, sustainable chemistry due to their ease of recycling, reusability, and environmental friendliness in comparison to homogenous catalysts [1,2]. The immobilization of metal particles on a polymeric carrier is an effective method for preparing heterogeneous catalysts. Chitosan is a preferred polymer carrier for dispersing nanoparticles because of its excellent physical properties, such as being insoluble in most solvents, and can be conveniently prepared as film, fibers, and microspheres [3,4]. Chitosan can be derivatized due to the large amount of embedded active hydroxyl groups and amino groups which are directly used as organic catalysts [5,6]. These functional groups can be modified into schiff bases [7,8], to enhance the ability to chelate ions or elementary substances. There are several reports on the application of chitosan-supported metal catalysts, which include the reduction of nitrobenzene [9,10], epoxidation of olefins [11], Suzuki cross-coupling reactions [12], Heck cross-coupling reactions [13], Knoevenagel condensation [14], and Michael addition [15,16]
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