Acid–base bifunctional catalysis by a heteropolyacid and amines on the polyetheretherketone fiber for cleaner acceleration of the one-pot tandem reactions

Abstract

The development of highly efficient, economical and environmentally friendly catalytic systems is of great significance from the green chemistry point of view. In this paper, we presented a succinct approach to create a heterogeneous acid–base bifunctional catalyst for one-pot tandem reaction from the commercially available textile fiber. The ultra-high strength textile fiber polyetheretherketone (PEEK) was functionalized by a post-grafting method to combine two antagonistic active functions in a synergistic catalyst, and the resulting fiber samples were characterized in detail by morphology, mechanical properties, elemental analysis, X-ray photoelectron spectroscopy, inductively coupled plasma-atomic emission spectrometry, X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet–visible spectrum, nuclear magnetic resonance spectroscopy and thermogravimetric analysis, and further revealed that the amines and the heteropolyacid were immobilized by acid–base interactions in the PEEK surface layer with sufficient stability. Moreover, the acid–base bifunctional catalyst can be successfully applied in the acceleration of the one-pot tandem deacetalization–Knoevenagel reactions with high-efficiency (lower catalyst dosage 0.3 mol%, higher product yields 81–92%), whereas the homogeneous catalysts were unable to initiate the reaction due to their mutual neutralization in solution, and the catalytic mechanism was elucidated by comparison. Furthermore, the fibrous catalyst could maintain its activities more than 10 cycles with a simple post-processing, and the mediated system was capable of enlarging to the gram-scale, which are envisaged for industrial operations and cleaner productions.