Chemoselective Hydrogenation of Nitroarenes to Arylamines Using Manganese Nanocatalyst and Molecular Hydrogen

This work presents an efficient and sustainable heterogeneous manganese nanocatalyst (Mn 3 O 4 -N@Al 2 O 3 ) for the selective hydrogenation of various nitroarenes to aryl amines using molecular hydrogen. The performance of the Mn 3 O 4 -N@Al 2 O 3 catalyst is evaluated through a series of reactions demonstrating excellent selectivity in hydrogenating the nitro group while preserving functional groups such as aldehyde, ketone, amides, carboxylic acid, nitrile, and olefins. The high selectivity and conversion were maintained even in a gram-scale reaction (∼1 g), performed for the synthesis of active pharmaceutical intermediates, including 2,6-dichloroaniline, 2,2′-(ethane-1,2-diyl)aniline, 2-aminobenzenethiol, and 3-chloro-4-fluoroaniline. Additionally, naphthalene-1,5-diamine and 4-amino-2,6-dichlorophenol were synthesized on a ∼1 g scale, which are key intermediates for producing naphthalene-1,5-diisocyanate and hexaflumuron, respectively. The analytical characterization data reveal that the catalysts consist of Mn 3 O 4 nanoparticles dispersed on the surface of Al 2 O 3 with an average size of 4.04 nm. The reaction mechanism was elucidated by tracking intermediates at different stages of the reactions, indicating a direct route without the formation of any condensation products.