Green Insights of Water-Mediated N-Arylation of 3-Amino-9-ethylcarbazole Using Fabricated Sulfated-Metal Oxides Fly Ash as a Sustainable Catalyst

The key innovative features of this work pertain to the creation of a sulfated SnO2–CeO2–fly ash nanocatalyst, which can be successfully reused as a sustainable catalyst for N-arylation of the industrial waste material. The present system allows N–arylation of 3-amino-9-ethylcarbazole using water as a medium under relatively mild conditions, without the need for costly metal complexes, solvents, ligands, harsh conditions, or handling in an inert atmosphere for conventional coupling reactions. The co-precipitation of SnO2 and CeO2 with fly ash is significant, as the catalyst offers synergistic catalytic properties such as redox activity, oxygen-vacancy active sites, surface acidity, and oxygen mobility, which are important to activate aryl halides and form a C–N bond. The catalyst was also applicable to substituted aryl halides with 79–97% yield. The catalyst was easily recovered and reused in seven subsequent cycles, giving a 95% yield in the seventh cycle with little change in crystal structure and morphology. In this way, the scientific value of this work not only relies on the successful achievement of N-arylation but also on the translation of a waste-derived, water-mediated, ligand-free, recyclable heterogeneous catalytic platform between valorization of fly-ash waste, green chemistry, and sustainable synthetic C–N bond formation for industrial scale.