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

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 TiO2–ZrO2 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.

Ni-Based Nanoparticles Catalyzed Hydrodeoxygenation of Ketones, Ethers, and Phenols to (Cyclo) Aliphatic Compounds

“…Supported nanoparticles (NPs) represent an important class of heterogeneous catalysts, which are extensively used for variety of chemical processes. − These notable achievements in metal–supported nanocatalysts and their significant advantages inspired us to develop a potential non-noble metal-based HDO catalyst. To design the suitable earth abundant metal-based HDO nanocatalyst, a library of Fe-, Co-, Ni-, and Cu-based nanoparticles was prepared (Table S1) and tested in the hydrodeoxygenation of acetophenone ( 1A ) to ethylcyclohexane ( 1B ) as a model reaction.…”

An Alternative Approach to Synthesize Sildenafil via Improved Copper-Catalyzed Cyclization

“…The subsequent workup necessitates an aqueous washing stage, leading to the generation of a waste stream comprising inorganic acids. This waste stream poses environmental challenges due to its unfriendly impact or may incur substantial costs for treatment. − Subsequently, acylation of the 4-amino-1-methyl-3-propyl-1 H -pyrazole-5-carboxamide with 2-ethoxybenzoyl chloride yielded intermediate compound 8 , which was cyclized under basic conditions to give pyrazolepyrimidinone 2 in 17.5% overall yield. In an improved commercial process, the sulfonamide compound was synthesized at an early stage by chlorosulfonation of 2-ethoxybenzoic acid.…”

Continuous-flow dehydrative amidation between carboxylic acids and amines using modified mixed metal oxides as solid acid catalysts

“…‡ Sulfonic acid-functionalized resin or silica gel and representative metallosilicate SiO 2 -Al 2 O 3 were found to be ineffective. A molybdenum(VI)-modified Ti-Zr mixed oxide, which showed unique and effective solid acid catalysis in continuous-flow aromatic nitration reactions in our group, 24,25 displayed promising activity especially when a low amount of solvent was used (entries 4 and 5). After examining various oxide composites of titanium, zirconium, silicon, and tin (entries 6-11), it was finally found that the 12 wt% Mo(VI) species-immobilized ZrO 2 -SnO 2 mixed oxide gave the corresponding amide almost quantitatively (entry 12).…”