Chemoselective hydrogenation of nitroarenes under industrially viable conditions is one of the attractive reaction for chemical, pharma, and pesticide industries. Herein, we report a reusable, stable, and renewable carbon-supported cobalt nanocatalyst (Co/MA-800) for the chemoselective reduction of structurally diverse nitroarenes with molecular hydrogen. The Co/MA-800 nanocatalyst was prepared via simple and straightforward carbonization of macroalgae and characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, H 2 -temperature programmed reduction, N 2 adsorption−desorption, and Raman spectroscopy. The cobalt content in Co/MA-800 is determined by inductively coupled plasma-atomic emission spectroscopy analysis. Furthermore, we show the hydrogenation of four marketed nitro pharmaceuticals that were selectively transformed to the respective primary anilines in excellent yields. We also demonstrate the synthesis of two industrially relevant key pharma intermediates on the ∼1 g scale, which are further employed in the preparation of drug compounds such as Linezolid and Tizanidine. The Co/MA-800 nanocatalyst was also active for the reductive amination of bezaldehyde and nitroarenes to achieve imines in good yields. In addition, the Co/MA-800 nanocatalyst is recycled 5 times without significant drop in catalytic activity.

Methanol is a potential hydrogen source and C1 synthon, which finds interesting applications in both chemical synthesis and energy technologies. The effective utilization of this simple alcohol in organic synthesis is of central importance and attracts scientific interest. Herein, we report a clean and cost‐competitive method with the use of methanol as both C1 synthon and H2 source for selective N‐methylation of amines by employing relatively cheap RuCl3.xH2O as a ligand‐free catalyst. This readily available catalyst tolerates various amines comprising electron‐deficient and electron‐donating groups and allows them to transform into corresponding N‐methylated products in moderate to excellent yields. In addition, few marketed pharmaceutical agents (e. g., venlafaxine and imipramine) were also successfully synthesized via late‐stage functionalization from readily available feedstock chemicals, highlighting synthetic value of this advanced N‐methylation reaction. Using this platform, we also attempted tandem reactions with selected nitroarenes to convert them into corresponding N‐methylated amines using MeOH under H2‐free conditions including transfer hydrogenation of nitroarenes‐to‐anilines and prepared drug molecules (e. g., benzocaine and butamben) as well as key pharmaceutical intermediates. We further enable one‐shot selective and green syntheses of 1‐methylbenzimidazole using ortho‐phenylenediamine (OPDA) and methanol as coupling partners.

Despite considerable achievements in the hydrogenation of aromatic hydrocarbons over the past few years, the ability to hydrogenate arene or heteroarene rings in a highly selective manner in the presence of other reducible sites or without harming the remaining molecular structure has long been a major challenge. Such chemoselectivity and functional group tolerance is highly desirable for enabling direct access to key building blocks of polymers and pharmaceutical agents. For achieving such high selectivity, the development of suitable catalysts is of central importance. Herein, we report a convenient method for the scalable preparation of ruthenium oxide (RuO2) nanoparticles supported on pine needle char (PNC) by simple impregnation of ruthenium salt on unactivated PNC, a solid byproduct (biochar) obtained in the slow pyrolysis of biomass pine needles. The resulting RuO2-based nanocatalyst (RuO2@PNC) exhibited remarkable activity and high selectivity for the hydrogenation of more than 50 challenging arenes and heteroarenes, including biomass-derived aromatic compounds (e.g., 4-n-propylphenol, furfuryl alcohol, and 2-methyl furan). The synthetic value of this transformation is showcased for the hydrogenation of arene mixture present in petroleum refineries or coal tars as well as biomass-derived oils (bio-oils) with enriched furfural, ether, and phenol derivatives. Under optimized conditions, the performance of this new catalyst was compared with state-of-the-art commercial catalysts such as Ru/C, Pd/C, and Raney nickel and found that RuO2@PNC is more superior and selective. Furthermore, the catalyst is easily recovered and reused up to four cycles.