Catalytic Hydrogenation of p-Chloronitrobenzene to p-Chloroaniline Mediated by γ-Mo₂N

Abstract

Promoting the production of industrially important aromatic chloroamines over transition-metal nitrides catalysts has emerged as a prominent theme in catalysis. This contribution provides an insight into the reduction mechanism of p -chloronitrobenzene ( p -CNB) to p -chloroaniline ( p -CAN) over the γ-Mo 2 N(111) surface by means of density functional theory calculations. The adsorption energies of various molecularly adsorbed modes of p -CNB were computed. Our findings display that, p -CNB prefers to be adsorbed over two distinct adsorption sites, namely, Mo-hollow face-centered cubic (fcc) and N-hollow hexagonal close-packed (hcp) sites with adsorption energies of −32.1 and −38.5 kcal/mol, respectively. We establish that the activation of nitro group proceeds through direct pathway along with formation of several reaction intermediates. Most of these intermediaries reside in a significant well-depth in reference to the entrance channel. Central to the constructed mechanism is H-transfer steps from fcc and hcp hollow sites to the NO/–NH groups through modest reaction barriers. Our computed rate constant for the conversion of p -CNB correlates very well with the experimental finding (0.018 versus 0.033 s –1 at ∼500 K). Plotted species profiles via a simplified kinetics model confirms the experimentally reported high selectivity toward the formation of p -CAN at relatively low temperatures. It is hoped that thermokinetics parameters and mechanistic pathways provided herein will afford a molecular level understanding for γ-Mo 2 N-mediated conversion of halogenated nitrobenzenes into their corresponding nitroanilines; a process that entails significant industrial applications.

Recent Progress on Transition Metal Nitrides Nanoparticles as Heterogeneous Catalysts

“…Density functional theory calculations were performed by Altarawneh et al [54] who studied the hydrogenation of p-CNB to p-CAN over the model γ-Mo 2 N(111) surface. The results showed that adsorption of p-CNB is thermodynamically favoured over Mo-hollow face-centered cubic (fcc) and N-hollow hexagonal close-packed (hcp) sites with adsorption energies of −32.1 and −38.5 kcal/mol, respectively.…”

Thiophene Modification of the Pt/SOD Catalyst to Enhance Catalytic Selectivity in Hydrogenation Reactions

“…Generally, p-chloronitrobenzene preferred to adsorb onto bare Pt metal surface with thermodynamically favorable flat-lying geometry via the πelectron interaction between Pt metal and the moiety of benzene group. 54 This parallel geometry would facilitate the activation of the nitro group and C−Cl bond simultaneously, perhaps resulting in the hydrogenation of the nitro group and dechlorination of the C−Cl bond occurrence at the same time. One of the feasible ways to promote catalytic selectivity was to design the surface environment of Pt metal to avoid such parallel adsorption conformation and better to adsorb onto the Pt surface only with the end of the nitro group.…”

“…DFT calculations combined with designed control experiments were conducted to reveal the intrinsic role of modified thiophene in the enhancement of catalytic selectivity of Pt/SOD-thiophene in this transformation. Generally, p -chloronitrobenzene preferred to adsorb onto bare Pt metal surface with thermodynamically favorable flat-lying geometry via the π-electron interaction between Pt metal and the moiety of benzene group . This parallel geometry would facilitate the activation of the nitro group and C–Cl bond simultaneously, perhaps resulting in the hydrogenation of the nitro group and dechlorination of the C–Cl bond occurrence at the same time.…”

Pre-Coking Strategy Strengthening Stability Performance of Supported Nickel Catalysts in Chloronitrobenzene Hydrogenation

“…The gas-phase selective hydrogenation of 1,2-dichloro-4-nitrobenzene (DCNB) to 3,4-dichloroaniline (DCAni) was selected as a model reaction to assess the benefit of the carbon protective layer. We noted that although many different solid catalysts have been reported for the selective hydrogenation of different functionalized nitrobenzenes in the literature [1,2,5,11], there are no widely recognized benchmark systems. In particular, studies on the continuous-flow hydrogenation of DCNB were scarce, though there exists a very recent paper by Duan and co-workers [33].…”

“…Halogenated anilines and their derivatives, such as chloroanilines and dichloroanilines, represent a class of important high-value intermediates for the synthesis of pharmaceutical ingredients, synthetic rubber, dyes, pesticides, etc. [1][2][3] Typical synthetic routes for these highly functionalized molecules are based on a two-step approach, i.e., the nitration of chlorobenzenes or dichlorobenzenes followed by the chemoselective hydrogenation of the nitro group. The hydrogenation process is traditionally realized by the use of stoichiometric reducing agents, including Fe, Zn, Sn, or hydride reagents [4], which unfortunately is environmentally unsustainable due to the generation of substantial amounts of harmful chemical wastes.…”