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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.

Developing a new environmentally friendly process for benzene nitration to nitrobenzene has been highly desirable for a long time. In this work, NO 2 was used as a nitration agent to replace traditional nitric acid, and different mesoporous SiO 2 and their supported heteropoly acid (salt) were employed to catalyze benzene nitration to nitrobenzene. Several typical catalysts were characterized using XRD, BET and FT-IR, and the acid amounts of the various catalysts were determined. The effects of various factors such as different catalysts, the molar ratio of benzene to NO 2 , reaction temperature, reaction time, HPW loading, the acid amounts of the catalyst and the reuse of the catalyst on the nitration reaction have also been systematically examined. The results indicate that the supported HPW/MCM-41 catalysts exhibit a remarkably synergistic catalytic performance on the nitration reaction of benzene to nitrobenzene. In particular, the 50%HPW/MCM-41 catalyst gives the best results with 73.4% benzene conversion and 98.8% selectivity to nitrobenzene under the optimal reaction conditions. Moreover, the mesoporous structure of MCM-41 was retained under the high loading of HPW. The possible reaction mechanism for the nitration reaction of benzene with NO 2 over HPW/MCM-41 is suggested in the present work. This method provides a promising strategy for the preparation of nitro-aromatic compounds from a catalytic nitration reaction by using NO 2 as the nitration reagent.

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