Sulfonated litchi exocarp carbon as solid acid catalyst to produce dihydropyrimidinones via Biginelli reaction

The sulfonation of a partly carbonized litchi shell with concentrated H 2 SO 4 afforded a carbon solid acid catalyst. Various physicochemical techniques, such as XRD, X-ray photoelectron spectroscopy, FT-IR spectroscopy, scanning electron microscopy (SEM), and N 2 physisorption measurements were used to study the structural properties of the prepared materials. It was an amorphous carbon material composed of aromatic carbon in random orientations. The catalytic behavior of the material was examined in the di-carbonyl compounds and urea with aromatic aldehydes for 3,4-dihydropyridine-2 (1H)-ones (DHPMs) production. Sulfonic acid groups were present on the surface at a density of 0.82 mmol/g, which led to a high DHPMs conversion efficiency of 95% at SO 3 H-CL at 80 °C after 3.5 h. More importantly, SO 3 H-CL has satisfying recyclable features and could maintain an 83% yield of its initial catalytic activity in the 6th catalytic run.