Liquid-phase Catalytic Continuous-Flow Aromatic Nitration Reactions with Conc. HNO3 on Modified Mixed-Metal Oxide Composites as High-Yielding Solid Acid Catalysts

Continuous-flow nitration of aromatic compounds catalyzed by a well-optimized solid acid catalyst with aqueous nitric acid under liquid phase was investigated. Using a suitable packed bed reactor system furnishing precolumn, the desired flow reaction proceeded to afford a nitroarene in a good yield by adopting Mo(VI)-supported TiO2-ZrO2 mixed-metal oxide. Further investigations toward enhance-ment on catalytic performance at higher weight hourly space velocity (WHSV) indicated that the mixed-metal oxide prepared by sol-gel method with calcination at 700 degrees C presented higher performances at 4.0 h-1 WHSV, and more than 90% yield was achieved. The turnover of the catalyst in long-term operation studies revealed that 87% yield was maintained when ca. 43-fold amount of toluene was delivered to the catalyst (g/g). A wide variety of aromatic compounds including both liquid and solid substances were enabled to convert into the corresponding nitroarene compounds by utilizing the developed system.

Automated summary

Continuous-flow nitration of aromatic compounds using aqueous nitric acid as the catalyst under liquid phase was studied. Mo(VI)-supported TiO2-ZrO2 mixed-metal oxide was used in a suitable packed bed reactor, and a good yield of nitroarene was obtained. Further investigations revealed that the mixed-metal oxide prepared by sol-gel method with calcination at 700 degrees C showed higher catalytic performance, with a yield of over 90% at 4.0 h-1 WHSV. Long-term operation studies showed a conversion rate of 87% with a 43-fold amount of toluene delivered to the catalyst.