(501e) Influence of Catalyst on the Mechanochemical Nitration of Toluene

Recently, it was shown that toluene can be nitrated mechanochemically employing a solvent-less process with a metal oxide catalyst and sodium nitrate as the nitronium source. This nitration method is attractive because it alleviates environmental concerns associated with the currently used techniques involving, most commonly, fuming nitric acid combined with sulphuric acid. Mechanochemical nitration is also scalable and the approach can be extended to nitrate other organic compounds. This effort is aimed to compare different metal oxide catalysts and clarify the mechanism of mechanochemical nitration of toluene. Metal oxides with different Lewis and Bronsted acidities, densities and oxidation states were tested as in experiments. The oxides considered included MoO₃, WO₃, V₂O₅, TiO₂, Bi₂O₃, MnO₂, Fe₂O₃, γ-Al₂O₃, and zeolites HZSM-5(Si/Al-39) and HZSM-5(Si/Al-350). Experiments were performed in a planetary mill. Detectable nitration of toluene occurred only with MoO₃, WO₃, and V₂O₅. For these oxides, the specific surface areas were measured after milling runs using BET method. The results suggest correlations between Bronsted acidity, surface area and yield of nitro-products. The experiments with varied milling times, altered concentration of H-bonds on the catalyst surfaces, and FTIR characterization of the evolving catalyst surfaces will also be presented and discussed.