Efficient and recyclable tetramethylguanidine-functionalized polyacrylonitrile fiber catalyst tailored for high-yield knoevenagel condensation

Abstract

This work presents a novel and recyclable tetramethylguanidine-modified polyacrylonitrile fiber catalyst (PAN_MGF), specifically designed for the Knoevenagel condensation reaction, which is a crucial method in organic synthesis for CC bond formation. The PAN_MGF was characterized through Fourier-transform infrared spectroscopy (FT-IR), elemental analysis (EA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and mechanical performance analysis. These results collectively confirmed the successful grafting of dimethylcyanamide as a guanidine precursor, which was subsequently converted into tetramethylguanidine functionalities on the PAN_MGF. Under mild conditions of 40 °C with H₂O as the solvent for a 12-hour reaction, the PAN_MGF exhibited superior catalytic performance, with a yield of 97 %. A thorough investigation of various benzaldehyde substrates revealed yields exceeding 90 % for both electron-withdrawing and electron-donating derivatives. These results demonstrate the remarkable substrate versatility and broad applicability of this catalyst. Moreover, when applied to other active methylene substrates, such as methyl cyanoacetate and malononitrile, the PAN_MGF achieved yields of 97 % and 98 %, respectively. These results collectively underscore its broad substrate scope across 28 different substrates and exceptional stability, which maintained a yield of 91.1 % even after 14 cycles, with an 89.9 % yield observed in the 15th cycle. Additionally, gram-scale experiments yielded a high separation efficiency of 93.6 %, further reinforcing the significant potential of PAN_MGF for practical applications in sustainable organic synthesis.