Liquid-phase Catalytic Continuous-Flow Aromatic Nitration Reactions with Conc. HNO<sub>3</sub> on Modified Mixed-Metal Oxide Composites as High-Yielding Solid Acid Catalysts
Haruro Ishitani, Masahiro Sasaya, Shū Kobayashi
Abstract
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 TiO 2 –ZrO 2 mixed-metal oxide. Further investigations toward enhancement 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 °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.