Nitrobenzene

About: Nitrobenzene is a research topic. Over the lifetime, 5285 publications have been published within this topic receiving 83368 citations. The topic is also known as: essence of mirbane & nitrobenzol.

In situ infrared monitoring of the solid/liquid catalyst interface during the three-phase hydrogenation of nitrobenzene over nanosized Au on TiO2

Abstract: The three-phase hydrogenation of nitrobenzene catalysed by nanosized gold over titania was investigated in a slurry. Simultaneous in situ ATR-FTIR monitoring of the liquid phase and at the solid/liquid catalyst interface identified the species adsorbed on the catalyst and those in the liquid phase during the reaction. Nitrosobenzene was not detected analytically while the spectroscopic measurements strongly indicated phenylhydroxylamine as an intermediate reacting before desorbing from the catalyst surface. Under the same reaction conditions, azobenzene and hydrazobenzene were identified as intermediates during the hydrogenation of azoxybenzene to aniline. When nitrosobenzene or phenylhydroxylamine was alternately fed as reactant, azoxybenzene was produced via a disproportionation route. With the former, azoxybenzene was not further reduced by hydrogen because nitrosobenzene deactivated the catalyst. Combined with H2 uptake, the spectroscopic measurements provided new insights into the reaction mechanism of the gold catalysed hydrogenation of nitrobenzene and an update of the corresponding kinetics.

Identifying competing aerobic nitrobenzene biodegradation pathways by compound-specific isotope analysis.

Abstract: Nitroaromatic compounds that contaminate soil and groundwater can be biodegraded by different, sometimes competing reaction pathways. We evaluated the combined use of compound-specific stable C and N isotope analysis to distinguish between enzymatic nitrobenzene oxidation by Comamonas sp. strain JS765 and partial reduction by Pseudomonas pseudoalcaligenes strain JS45 under aerobic conditions. Bulk 13C and 15N enrichment factors for nitrobenzene dioxygenation with JS765 were -3.9 per thousand +/- 0.09 per thousand (+/- 1sigma) and -0.75 per thousand +/- 0.09 per thousand, respectively. The corresponding primary apparent kinetic isotope effects (AKIE) of 1.0241 +/- 0.0005 for 13C and a secondary 15N AKIE of 1.0008 +/- 0.0001 are in very good agreement with the proposed enzymatic addition of dioxygen to the aromatic ring to form a cis-dihydrodiol in the rate-limiting step of nitrobenzene degradation. For the partial reduction pathway with JS45, epsilonC and epsilonN values were -0.57 per thousand +/- 0.06 per thousand and -26.6 per thousand +/- 0.7 per thousand. The 13C and 15N AKIEs amount to 1.0034 +/- 0.0003 and 1.0273 +/- 0.0008, respectively, and are consistent with the two-electron reduction and dehydration of the aromatic NO2 group to nitrosobenzene. The combined evaluation of delta13C and delta15N changes in nitrobenzene, based on the isotope enrichment behavior found in this laboratory study, provide an excellent starting point for assessing of the extent of nitrobenzene biodegradation via competing pathways in contaminated environments.

Effect of oxidant treatment of date pit active carbons used as Pd supports in catalytic hydrogenation of nitrobenzene

Abstract: Two active carbons from Algerian date pits prepared by chemical activation at moderate temperature (500-600 degrees C) with H3PO4 and ZnCl2 and one commercial active carbon (from Darco) have been oxidized with air at different temperatures (300-450 degrees C) and with nitric acid in severe conditions during a short time. It has been demonstrated that air treatment generates surface oxygenated groups (XPS) that have an acidic character (simplified Boehm titration), without degrading the specific surface area (BET). Each active carbon has an optimal oxidation temperature depending on its activation procedure and corresponding to 20% in weight loss during the oxidation process. This optimal temperature achieves the highest surface oxygen content, which is directly correlated to the global acidity. It also means that when the support is loaded with 5% Pd by incipient wetness method, the catalyst exhibits the best activity for the liquid phase hydrogenation of nitrobenzene to aniline. In general, the metallic dispersion of the catalysts (CO chemisorption) remained appreciable even after oxidizing treatments. Exception is noted when nitric acid is used as oxidant while the active carbon has been prepared using zinc chloride. (c) 2005 Elsevier B.V. All rights reserved.

Gas phase synthesis of para-aminophenol from nitrobenzene on Pt/zeolite catalysts

Abstract: A single-step reaction of nitrobenzene into para-aminophenol was carried out in the gas phase using metal-supported zeolite as a bi-functional catalyst. A significant amount of para-aminophenol was produced with aniline and ortho-aminophenol without using any environmentally undesirable liquid acid. For the selective formation of para-aminophenol, Pt supported on H-ZSM-5 was the best combination of metal and acid catalysts. The selectivity to para-aminophenol depended greatly on the Al concentration of H-ZSM-5; that is, HZSM-5 with intermediate Al concentration gave the highest selectivity. Pt particles on H-ZSM-5 were characterized by the measurements of adsorbed CO, TEM and IR spectra.