Proton sponge functionalized polyacrylonitrile fibers as an efficient and recyclable superbasic catalyst for Knoevenagel condensation in Water

Abstract

Fiber catalysts with high catalytic activity and good recyclability have attracted much attention. In this work, proton sponge 1,8-bis(dimethylamino)naphthalene functionalized polyacrylonitrile fiber is prepared to construct a superbasic microenvironment, which is applied to catalyze the Knoevenagel condensation in water for the synthesis of α,β-unsaturated compounds. Different characterization techniques of XPS, 13C solid-state NMR, FTIR, SEM etc. Are used to verify the successful grafting of the proton sponge during modification as well as evaluate the stability of the fiber catalyst in specific application. The fiber catalyst exhibits distinctly higher catalytic activity and efficiency in water than in other solvents, with a low catalytic dosage of 5 mol% under room temperature within 3 h. Besides, a synergistic microenvironment can be formed between the hydrophilic polar surface of the fiber and the superbasic catalytic sites, promoting the efficient catalysis of Knoevenagel condensation reaction. In addition, the fiber possesses high reusability that it can be easily recovered and reused for at least 10 times without obvious loss of its catalytic activity. More interestingly, the fiber can be fixed in a reactor to catalyze the Knoevenagel condensation, in which process pure α,β-unsaturated compounds are continuously obtained by simple filtration, avoiding the use of toxic solvents and time-consuming column chromatography, which presents great potential in cleaner and more efficient production. In brief, with such advantages as high catalytic activity, simple separation operation and good economic efficiency, the proton sponge modified fiber is fairly attractive in fixed-bed reactors in cleaner industrial production.