Synthesis of flow‐compatible Ru-Me/Al2O3 catalysts and their application in hydrogenation of 1-iodo-4-nitrobenzene

Abstract

The development of an active, selective, and long-term stable heterogeneous catalyst for the reductive hydrogenation of substituted nitrorarenes in continuous operation mode is still challenging. In this work, Ru based nanoparticles catalysts promoted with different transition metals (Zn, Co, Cu, Sn, or Fe) were supported on alumina spheres using spray wet impregnation method. The freshly prepared catalysts were characterized using complementary methods including scanning transmission electron microscopy (STEM) and temperature programmed reduction (TPR). The hydrogenation of 1-iodo-4-nitrobenzene served as model reaction to assess the catalytic performance of the prepared catalysts. The addition of the promotor affected the reducibility of Ru nanoparticles as well as the performance of the catalyst in the hydrogenation reaction. The highest yield of 4-iodoaniline (89 %) was obtained in a continuous flow process using Ru-Sn/Al2O3. The performance of this catalyst was also followed in a long-term experiment. With increasing operation time, a catalyst deactivation occurred which could only briefly compensate by an increase of the reaction temperature.

Copper-Catalyzed Continuous-Flow Transfer Hydrogenation of Nitroarenes to Anilines: A Scalable and Reliable Protocol

“…Aniline derivatives are relevant intermediates in the synthesis of dyes, pharmaceuticals, agrochemicals, and other fine compounds, and the reduction of aromatic nitroarenes is clearly the most commonly used method of preparation. Given the importance of this process in both industry and academia, it is not surprising that several catalytic flow-chemistry hydrogenation protocols have been reported over the past decade. , The reaction is usually performed under either palladium, − platinum or RANEY nickel, , or Ni/SiO 2 catalysis, giving high yields, and few examples also reported gold, ruthenium, , and cobalt . All reactions are performed in dedicated high-pressure resistant reactors at variable temperatures from rt to 110 °C.…”

“…Given the importance of this process in both industry and academia, it is not surprising that several catalytic flow-chemistry hydrogenation protocols have been reported over the past decade. 16 , 17 The reaction is usually performed under either palladium, 18 − 21 platinum 22 or RANEY nickel, 23 , 24 or Ni/SiO 2 25 catalysis, giving high yields, and few examples also reported gold, 26 ruthenium, 27 , 28 and cobalt. 29 All reactions are performed in dedicated high-pressure resistant reactors 30 at variable temperatures from rt to 110 °C.…”

Highly Selective Electrocatalytic Reduction of Substituted Nitrobenzenes to Their Aniline Derivatives Using a Polyoxometalate Redox Mediator

“…Aromatic amines (anilines) are key nitrogen-containing building blocks for the production of pharmaceuticals, dyes, and polymers, with a prime example being the synthesis of paracetamol, a derivative of 4-aminophenol. − Typically, aromatic amines are synthesized through the reduction of the corresponding nitroarene compounds using heterogeneous catalysts at elevated temperatures and pressures and employing hydrogen gas as the reductant. , Although these conditions give good results for the reduction of unfunctionalized nitrobenzene to aniline, the reduction of more complex (substituted) nitroarenes to their aniline products is much more difficult to achieve with high selectivity. , From among the substituted nitroarenes with reducible groups (e.g., carbonyls, esters, amines, and halide groups), the most challenging substrates are the halogenated aromatics, as the hydro-dehalogenation reaction can occur very readily under the standard high temperature and pressure reduction conditions, leading to a marked drop in selectivity. − …”