Nitroaromatic reduction

Uniform Dispersion of Anisotropic CuO/SBA-15 Nanocomposites for Nitroaromatic Reduction... 

Nitroaromatic Reduction Nitroaromatics constitute an important class of potential environmental contaminants, because of their wide use in agrochemicals, textile dyes, munitions, and other classes of industrial chemicals. Reduction of nitroaromatics produces amines, throngh a series of electron transfer reactions with nitroso and hydroxylamines as intermediates (Fig. 13.1). Compared to the parent nitroaromatic compound, all intermediates typically reduce readily (Larson and Weber 1994). 

Devlin JF, Klausen J, Schwarzenbach RP. Kinetics of nitroaromatic reduction on granular iron in recirculating batch experiments. Environ Sci Technol 1998 32 1941-1947. 

Nitroaromatic reduction has been observed in natural systems and in well defined laboratory model systems. Nitro reductions are known to be mediated by anaerobic soils and sediments (Wahid and Sethunathan, 1979 Wahid et al., 1980 Adhya et al., 1981a and 1982b Gambrell et al., 1984 Wolfe et al., 1986 Sanders and Wolfe, 1985 Weber, 1988), sulfide minerals (Yu and Bailey, 1992), sewage sludge (Geer,... 

Nitroaromatic reduction has also been demonstrated to occur in mineral systems (Yu and Bailey, 1992). Laboratory studies indicated that the order of reactivity for the reduction of nitrobenzene by several sulfide minerals was Na2S>MnS>ZnS> M0S2. This order of reactivity paralleled the solubility of the mineral sulfides, which suggests that reduction rates were dependent on sulfide ion concentrations in solution. The sulfide ions and other sulfur species were hypothesized to play a bridging role for the transfer of electrons from the mineral to nitrobenzene. 

Nitro functions are easily reductively alkylated and a number of alkylated anilines are made industrially starting with the appropriate nitroaromatic in the ketone as solvent. The addition reaction can occur at the hydroxylamine intermediate as well as the aniline. A process step is saved by beginning with the nitro compound. 

Aromatic nitroso compounds usually are considered to be intermediates in the hydrogenation of a nitroaromatic compound to the aromatic hydroxyl-amine or amine. However, nitroso compounds do not accumulate in these reductions, suggesting that they are reduced more easily than are nitro compounds. Catalysts effective for the nitro group should also be effective for nitroso. 

Reduction of the nitroaromatic with NaBH4 in DMSO or Zn in NaOH/EtOH leads to the hydrazo derivative and treatment with aqueous HC1 gives benzidine rearrangement.115... 

Under the chosen conditions aromatic compounds are nitrated to nitroaromatics [1]. The detection of rotenone [1] (see below) depends on the reduction of silver ions, incorporated into the layer, to metallic silver in the presence of ammonia [4]. The mechanism of the reaction of many substances leading to fluorescent derivatives has not yet been elucidated [2],... 

Two important examples of reductive metabolism of xenobiotics are the reductive dehalogenation of organohalogen compounds, and the reduction of nitroaromatic compounds. Examples of each are shown in Figure 2.13. Both types of reaction can take place in hepatic microsomal preparations at low oxygen tensions. Cytochrome P450 can catalyze both types of reduction. If a substrate is bound to P450 in the... 

Hetherington, L.H., Livingstone, D.R., and Walker, C.H. (1996). Two and one-electron dependant reductive metabolism of nitroaromatics by Mytilus edulis, Carcinus maenas and Asterias rubens. Comparative Biochemistry and Physiology 113, 231-239. 

Glaus M A, CG Heijman, RP Schwarzenbach, J Zeyer (1992) Reduction of nitroaromatic compounds mediated by Streptomyces sp. exudates. Appl Environ Microbiol 58 1945-1951. 

Schwarzenbach RP, R Stierliu, K Lanz, J Zeyer (1990) Quinone and iron porphyrin mediated reduction of nitroaromatic compounds in homogeneous aqueous solution. Environ. Sci. Technol. 24 1566-1574. 

Rafii F, W Franklin, RH Hetlich, CE Cerniglia (1991) Reduction of nitroaromatic compounds by anaerobic bacteria isolated from the human gastrointestinal tract. Appl Environ Microbiol 51 962-968. 

Partial reduction by Clostridia has been demonstrated and has already been discussed in Chapter 9, Part 5. The effectiveness of Clostridia in the anaerobic digestion of a number of nitroaromatics has prompted development of a procedure for the production of spores of Clostridium bifermentans, and a medium for their effective production has been developed (Sembries and Crawford 1997). 

Various other reducing methods are employed for the conversion of (3-nitro alcohols to amino alcohols, namely, electrochemical reduction.107 The selective electrohydrogenation of ni-troaliphatic and nitroaromatic groups in molecules containing other groups that are easy to hydrogenate (triple bond, nitrile, C-I) are carried out in methanol-water solutions at Devarda copper and Raney cobalt electrodes (Eq. 6.55).107... 

Other bacteria. Intestinal bacteria may play a critical role in the metabolic activation of certain nitroaromatic compounds in animals (119) and several reports have appeared on the metabolism of nitro PAHs by rat and human intestinal contents and microflora (120-123). Kinouchi et al. (120) found that 1-nitropyrene was reduced to 1-aminopyrene when incubated with human feces or anaerobic bacteria. More recently, Kinouchi and Ohnishi (121) isolated four nitroreductases from one of these anaerobic bacteria (Bacteroides fragilis). Each nitroreductase was capable of converting 1-nitropyrene into 1-aminopyrene, and one form catalyzed the formation of a reactive intermediate capable of binding DNA. Howard ej al. (116) confirmed the reduction of 1-nitropyrene to 1-aminopyrene by both mixed and purified cultures of intestinal bacteria. Two additional metabolites were also detected, one of which appeared to be 1-hydroxypyrene. Recently, similar experiments have demonstrated the rapid reduction of 6-nitro-BaP to 6-amino-BaP (123). 

Eqs. 9 and 10 make clear predictions about the dependence of quenching rate constants on the free energy change in the quenching step. One way of testing the theory is to observe the quenching of the excited state by a series of related quenchers where the parameters kq(0), K, and k j) should remain sensibly constant and yet where the potentials of the quenchers as oxidants or re-ductants can be varied systematically. Such experiments have been carried out, most notably with the MLCT excited state, Ru(bpy)3 + (1). The experiments have utilized both a series of oxidative nitroaromatic and alkyl pyridinium quenchers, and a series of reductive quenchers based on aniline derivatives. From the data and known redox potentials for the quenchers, plots of RTlnk q vs. 

Rafii F, Cemiglia CE (1995) Reduction of azo dyes and nitroaromatic compounds by bacterial enzymes from the human intestinal tract. Env Health Persp 103 17-19... 

Reduction of quinones, quinonimines, nitroaromatics, azoaromatics, and oxidized aromatic heterocycles Oxidation of phenols and amines... 

Schwarzenbach, R. P., R. Stierli, and J. Zeyer (1990), "Quinone and Iron Porphyrine Mediated Reduction of Nitroaromatic Compounds in Homogeneous Aqueous Solution , Env. Sci. Technol. 24/10, 1566-1574. 

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