Efficient Catalytic Hydrogenation of Nitroaromatic Using Cobalt Single-atom Derived from Metal-organic Framework

Aromatic amines and their derivatives are widely used as important active intermediates in drugs, dyes and herbicides.Therefore, the development of highly efficient, low-cost, and highly selective catalysts for the hydrogenation of nitroaromatic hydrocarbons is desirable.In this study, Zn-Co metal-organic framework (MOF) materials were synthesized with Zn 2+ /Co 2+ as the metal source and 2-methylimidazole as an organic ligand at room temperature.Then, a Co catalyst (Co-N-C) was prepared by in-situ pyrolysis using the Zn-Co MOF as a sacrificial template under a nitrogen atmosphere.Aromatic nitro compounds can be selectively converted to the corresponding aromatic amines using ethanol as solvent, hydrazine hydrate as a hydrogen source, and Co-N-C as catalyst.The Co-N-C synthesized by pyrolysis at 1000 ℃ possesses the best catalytic activity.The effects of solvent and reaction time and the amount of Co-N-C, ethanol, and hydrazine hydrate on the catalytic system were investigated.The catalytic effect was the best when 5 mg Co-N-C, 4 mL ethanol, and 4 mmol hydrazine hydrate were added to the system, and the yield of aniline reached 100% after 10 h.Thirty-one different types of nitro-aromatic compounds, including ortho-, meta-, and para-substituted nitroaromatics with electron-donating or electron-withdrawing substituents, nitrobenzene derivatives with other reducible functional groups, and heterocyclic and polycyclic aromatic compounds, were obtained in high yields under this system, which has a wide substrate scope.In addition, the flutamide and nilutamide derivatives and aminoglutethimide were prepared in excellent yields using the Co-N-C catalytic system.The feasibility of the Co-N-C catalytic system was demonstrated using a gram-scale reaction.Cycling and anti-leaching experiments demonstrated that the Co-N-C material has excellent stability and anti-leaching properties, and acts as a reusable heterogeneous catalyst, which can be easily separated and collected by centrifugation.In addition, two reaction mechanisms of direct reduction and condensation reduction of nitro-aromatics using a Co-N-C catalyzed system were proposed by testing the reaction process.This research provides an efficient, simple, and green method for the hydrogenation reduction of nitroaromatics.