Abstract
The combination of chitosan as a renewable heterogeneous catalyst and ionic liquid as a “green” solvent was employed for the Knoevenagel reaction. The chitosan catalyst was characterized by various techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and elemental analysis. Excellent conversions were achieved under mild conditions without the need for an inert atmosphere. There was no contribution from leached active species, and conversion was only being possible in the presence of the solid catalyst. The chitosan catalyst as well as the ionic liquid solvent could be recovered in essentially pure form after being used in the reaction, and each of them could be reused several times without a significant degradation in efficiency.
Highlights
Room temperature ionic liquids have been considered as potential green alternatives to conventional volatile organic solvents during the last decade [1,2,3,4,5]
The chitosan catalyst as well as the ionic liquid solvent could be recovered in essentially pure form after being used in the reaction
The chitosan catalyst was characterized using a variety of different techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), nitrogen physisorption measurements, and elemental analysis
Summary
Room temperature ionic liquids have been considered as potential green alternatives to conventional volatile organic solvents during the last decade [1,2,3,4,5]. The Knoevenagel condensation between aldehydes or ketones with activated methylene compounds is one of important carbon-carbon forming reactions in organic synthesis [39, 40]. This reaction is catalyzed by alkali metal hydroxides or by organic bases under homogeneous conditions with the attendant difficulties in catalyst recovery and recycling [41]. ISRN Organic Chemistry transitional metal-catalyzed reactions [55,56,57,58], and it was used as a solid base catalyst for the aldol condensation reaction [59] All of these processes were still carried out in conventional volatile organic solvents. Both the catalyst and the solvent could be reused several times without a significant degradation in performance
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