Controlled nitration of anisole over HNO3/PO4/MoO3/SiO2/solvent systems

•Solids composed of PO43− built in the surface Mo∞O3∞ lattice were obtained.•The solids were characterized by XRD, 31P MAS NMR and Raman techniques.•The PO4/MoOx/SiO2 is effective in nitration of anisole over 65% nitric acid.•Selectivity to 4-nitroanisoles can be easily controlled.•The PO4/MoOx/SiO2 is stable and reusable catalyst.

Nitroanisoles have wide applications in pharmaceuticals, perfumery and production of corresponding amines used extensively in dye industry. The presence of activated methoxy group in the aromatic ring, causes the nitration of anisole to be complex and difficult to control. The catalysts obtained by mixing phosphoric acid with ammonium molybdate, and impregnating the solution on silica gel, are composed of PO43− ions built in the structure of surface Mo∞O3∞ lattice (heteropolyanion structure-like species). Using various amounts of the molybdenum species, it is possible to manipulate the catalyst acidity and simultaneously its activity. At room temperature, for 30 min with using fuming nitric it is possible to obtain ca. 90% anisole conversion with 62% selectivity to 4-nitroanisole. When 65% HNO3 is used, the conversion decreases to 76%, however the selectivity to 4-nitroanisole increases to 74%. Another advantage of the obtained catalysts is the possibility of their effective reuse in the subsequent reactions.

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