Hydrogenation of Nitrobenzene to 4-Aminophenol over Supported Platinum Catalysts

Abstract

The conversion of nitrobenzene (NB) to p-aminophenol (PAP) takes place by way of an initial partial hydrogenation to produce phenylhydroxyl amine (PHA) which then undergoes an in situ acid-catalyzed rearrangement to PAP. This reaction is most commonly run using Pt/C catalysts in the presence of aqueous sulfuric acid and a surfactant to assist in dispersing the NB throughout the reaction medium. The yield of PAP is closely related to those reaction parameters which facilitate first the partial hydrogenation step and second the acid-promoted rearrangement before further hydrogenation to aniline can take place. The effect which a number of reaction parameters such as hydrogen pressure, reaction temperature, stirring rate, and the amounts of NB, the catalyst, and the surfactant present in the reaction mixture had on the rate and selectivity of the hydrogenation was examined. Optimization of these parameters led to the formation of PAP at a selectivity (PAP/AN) of 5.4 with a productivity of over 80,000 g PAP/g Pt/h.

New insight on the mechanism of the catalytic hydrogenation of nitrobenzene to 4-aminophenol in CH3CN–H2O–CF3COOH as a reusable solvent system. Hydrogenation of nitrobenzene catalyzed by precious metals supported on carbon

“…It is noteworthy that the best performing one, in terms of both catalytic activity and yield to 4-aminophenol, is Pt/C. This gives the best results also with the biphasic sulfuric acid nitrobenzene system [1][2][3][4][5][6]. Both Pd/C and Rh/C show high hydrogenation activity, but 4-aminophenol yields (in both cases) is lower than that observed in the presence of Pt/C.…”

“…4-Aminophenol is an important raw material for several products in the field of dyes, polymer and pharmaceutics [1][2][3]. For instance, paracetamol (N-acetyl-4-aminophenol) is a widely employed analgesic and antipyretic whose production is in continuous growth, particularly in the Far East region [4][5][6][7][8][9].…”

“…Till now, the selective hydrogenation of nitrobenzene is likely to be the most convenient from both economical and environmental point of view [1,2,[4][5][6][7][8][9]. The major concern of this process is, however, the use of H 2 SO 4 , which poses corrosion, safety, purification and environmental problems.…”

“…In addition, diluted sulfuric acid causes huge corrosion concern, with the consequent increased costs [1,2,[4][5][6]8,9]. Therefore, removal of H 2 SO 4 use is likely to be the most important target for the improvement of the process.…”

Highly Efficient Au/TiO2 Catalyst for One‐pot Conversion of Nitrobenzene to p‐Aminophenol in Water Media

“…Henke and Vaughen [11] showed that NB pathway is feasible using Pt/C catalyst in inorganic acid solution. [12] Meanwhile, corresponding kinetics was also carefully investigated, showing that hydrogenation rate is competitive against rearrangement rate, which limits the PAP selectivity even in concentrated acids. [12] Meanwhile, corresponding kinetics was also carefully investigated, showing that hydrogenation rate is competitive against rearrangement rate, which limits the PAP selectivity even in concentrated acids.…”