Pt/C‐catalyzed Selective Hydrogenation of Nitroarenes to N‐arylhydroxylamines under Mild Conditions

Abstract

The synthesis of N‐arylhydroxylamines through the in‐situ hydrogenation of nitroarenes over commercial Pt/C catalyst was investigated. The effects of various reaction conditions including hydrogen donor, solvent, catalyst dosage, temperature and reaction time on the selective hydrogenation of nitrobenzene (NB) to N‐phenylhydroxylamine (PHA) were systematically investigated. The results showed that the yield of N‐phenylhydroxylamine reached 87.2 % using hydrazine hydrate as hydrogen donor in N,N‐dimethylformamide solvent at 30 °C for 60 min. And the catalyst showed no obvious activity loss after a 6‐times recycle. Meanwhile, the developed methodology can also transform a range of nitroarenes to the corresponding N‐arylhydroxylamines in excellent yields (74–99 %).

Design and Synthesis of N-Doped Carbons as Efficient Metal-Free Catalysts in the Hydrogenation of 1-Chloro-4-Nitrobenzene

“…This requires the cleavage of the N-O bond, determining it to be the slow stage of the reaction. If the catalytic activity is not very high, there is a risk of phenylhydroxylamine accumulation leading to an increase in byproducts [ 39 ].…”

“…The analysis of the intermediates and products of the reaction under different experimental conditions has led to the conclusion that the direct route is preferred to the condensation route unless strong bases are present. However, the actual reaction mechanism is unclear and is still the aim of debate [ 38 , 39 , 40 ]. The accumulation of intermediate products is a general issue associated with the hydrogenation of nitroarenes.…”

“…This requires the cleavage of the N-O bond, determining it to be the slow stage of the reaction. If the catalytic activity is not very high, there is a risk of phenylhydroxylamine accumulation leading to an increase in byproducts [39]. The indirect pathway progresses through the condensation of nitrosobenzene and phenylhydroxylamine, producing azoxybenzene which will then be reduced to azo, hydrazo and amine compounds in a series of successive steps.…”