Metal-free solid base catalysis: Boron-doped graphitic carbon nitride for the efficient synthesis of ethyl coumarin-3-carboxylate

Abstract

In this work, boron doped graphitic carbon nitride materials (BgCN-x) were successfully prepared by thermal copolymerization of melamine and boric acid. The comprehensive characterization using various techniques, including powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), UV-Visible spectroscopy (UV-Vis), Field emission scanning electron microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDS), Field emission transmission electron microscopy (FETEM), and X-ray photoelectron spectroscopy (XPS) revealed the uniform doping of boron in the tri-s-triazine rings of g-C₃N₄ by substituting the carbon or nitrogen atoms. Furthermore, the basic site concentrations of the catalysts were evaluated using CO₂-TPD technique. The BgCN catalysts exhibited significantly enhanced catalytic activity in the base-catalyzed Knoevenagel condensation between salicylaldehyde and diethyl malonate for coumarin synthesis. This work underscores the potential of boron-doped or two-dimensional boron-dominant materials as promising candidates for metal-free heterogeneous base catalysis, paving the way for further advancements in the field.