Nitro aromatics, hydrogenation

M. T. Rreutzer, F. Kapteijn, J. A. Mouhjn, Fast gas-4iquid—sohd reactions in monoliths a case study of nitro-aromatic hydrogenation, Catal. Today 2005, 105, 421-128. 

Kreutzer MT, Kapteijn F, Moulijn JA. Fast gas-liquid-solid reactions in monoliths A case study of nitro-aromatic hydrogenation. Catalysis Today 2005 105 421-428. 

Nitro aromatics owe their great importance in organic synthesis for being intermediates for the generation of the respective anilines by hydrogenation [17, 61]. For instance, pharmaceuticals are produced via that route [61],... 

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

Figure 11.14 Formation of instable intermediates during the catalytic hydrogenation of nitro-aromatic compounds. The decomposition of phenyl hydroxyl amine (I) is shown in the thermogram at 70% of hydrogen uptake. The decomposition of the nitro aromatic compound (D) decreases as the hydrogenation progresses.

Nitro-polycyclic aromatic hydrocarbons, referred to as nitro-aromatic compounds hereafter, constitute one of the most troubling classes of environmental pollutants. They are derivatives of polycyclic aromatic hydrocarbons (PAHs) that contain two or more fused aromatic rings made of carbon and hydrogen atoms and at least one nitro group (Fig. 10.1). Concern about these compounds arises partly from their ubiquity nitro-aromatic compounds are released to the environment directly from a variety of incomplete combustion processes [1] and are also formed in situ by atmospheric reactions of PAHs [2]. Nitro-aromatic compounds have been found in grilled food in diesel, gasoline, and wood-smoke emissions and are commonly found in atmospheric particulate matter, natural waters, and sediment [3-8],... 

Aromatic nitroso compounds are, like aromatic nitro compounds, hydrogenated rapidly to the amines over palladium catalysts,200,201 as seen in an example shown in eq. 9.71. However, in contrast to the cases with aromatic nitro compounds, a kinetic... 

Irradiation of nitro aromatics produces excited states in which the nitro group oxygen can remove an accessible hydrogen. The resulting diradical can then undergo hydroxyl transfer to the substrate carbon. This process has been used to hydroxylate dammarane terpenes related to steroids, by preparing appropriate nitrophenyl esters of the substrates and then photolyzing (Scheme In Ae steroid series a... 

As might be expected, substitution of iodine by hydrogen in aryl iodides is easier than in aryl bromides. This is evident in selective reduction of chloroiodo aromatics (equation 62), - and especially bromoiodo aromatics (equation 63), and also in the selective reduction of iodonitro aromatics to nitro aromatics (equations 64 and 65). ... 

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