Heterogeneous Cobalt Nanocatalyst for Reductive Transformation of Nitroarenes to Aryl Amines Using Isopropanol as a Hydrogen Source

Abstract

Herein, we introduce an efficient catalytic transfer hydrogenation method using inexpensive, environmentally friendly, and readily available isopropyl alcohol as a hydrogen donor for selectively reducing diverse nitroarenes. The process employs a cobalt-based nanocatalyst (Co–N/Al₂O₃), synthesized via a simple impregnation method using cobalt nitrate, 1,10-phenanthroline, and γ-Al₂O₃ as precursors. This method proves highly effective in producing a wide range of aryl amines (35 examples), pharmaceutical intermediates (4 examples), and late-stage functional group transformations (1 example), with yields ranging from moderate to excellent (70–98%) across various scales. The catalyst was characterized using HR-TEM, powder XRD, XPS, H₂-TPR, N₂ adsorption–desorption, Raman spectroscopy, and ICP-OES techniques. These analyses confirmed the formation of Co₃O₄ nanoparticles. The exceptional performance of the Co–N/Al₂O₃ catalyst is attributed to its optimized textural, morphological, and acidic properties, which are superior to other catalysts. Mechanistic studies provided insights into the intermediates formed during different stages of the reaction and confirmed the indirect route (condensation mechanism). The recyclability studies of the catalyst were validated through experimental testing, demonstrating consistent efficiency over three consecutive cycles. This sustainable method offers a promising alternative to conventional hydrogenation processes that use molecular hydrogen.