Amidosulfonic acid supported on graphitic carbon nitride: novel and straightforward catalyst for Paal–Knorr pyrrole reaction under mild conditions

A novel heterogeneous acidic catalyst was prepared by in situ immobilization of amidosulfonic acid (NH 2 SO 3 H) on graphitic carbon nitride (g-C 3 N 4 ) under hydrothermal conditions. The textural morphology of NH 2 SO 3 H/g-C 3 N 4 nanocomposite was characterized via powder X-ray diffraction, FT-IR, TGA, EDX, and scanning electron microscopy. The spatial arrangement of the amidosulfonic acid on the surface of g-C 3 N 4 leads to the construction of a unique solid acid structure, resulting in a substantial enhancement of catalytic activity toward a high efficient preparation of pyrroles by Paal–Knorr reaction. The reactions undergo completion readily with good to excellent yields, with simple purification in an environmentally friendly manner. The NH 2 SO 3 H/g-C 3 N 4 nanocomposite can be readily recycled, and no noteworthy reduction in the catalytic activity detected after four runs. Graphic abstract