Solvent-Free, Low-Temperature, Highly Efficient Catalytic Nitration of Toluene with NO2 Promoted by Molecular Oxygen over Immobilized AlCl3–SiO2

A mild and highly efficient method for solvent-free low temperature catalytic nitration of toluene with NO2 promoted by molecular oxygen has been developed in the present work. The immobilized AlCl3–SiO2 catalyst was successfully synthesized by a chemical bonding method. The results indicated that the synergistic catalysis of molecular oxygen and catalyst remarkably improved the nitration efficiency. Under optimal conditions, 86.5% of toluene conversion with 100% of selectivity to mononitrotoluene was achieved at 35 °C. Furthermore, the immobilized 10% AlCl3–SiO2 catalyst exhibited excellent stability in this nitration process. Finally, the probable reaction mechanism for the catalytic nitration promoted by molecular oxygen over AlCl3–SiO2 was suggested. This work affords a simple, highly efficient, safe, and benign approach for the preparation of valuable mononitrotoluene under the mild conditions and has potential industrial application prospects.