Reduction of aromatic nitro compounds

The Zinin reduction is also usehil for the reduction of aromatic nitro compounds to amines in the laboratory. It requires no special equipment, as is the case with catalytic hydrogenations, and is milder than reductions with iron and acid. Usually ammonium or alkah sulfides, hydrosulftdes or polysulftdes are used as the reactant with methanol or ethanol as the solvent. 

Electrolytic reductions generally caimot compete economically with chemical reductions of nitro compounds to amines, but they have been appHed in some specific reactions, such as the preparation of aminophenols (qv) from aromatic nitro compounds. For example, in the presence of sulfuric acid, cathodic reduction of aromatic nitro compounds with a free para-position leads to -aminophenol [123-30-8] hy rearrangement of the intermediate N-phenyl-hydroxylamine [100-65-2] (61). 

Reduction of Aromatic Mitro Compounds to Aromatic Amines. Mild conditions and a large variety of catalysts effect reduction of aromatic nitro compounds to aromatic amines (see Amines byreduction). 

Reduction of aromatic nitro compounds may give products sensitive to air. Moder and Leonard (d5) stressed the importance of rigid exclusion of air during reduction of a nitro compound to a complex air-sensitive diamine in order to maximize the yield. It is quite likely that in these cases the oxidation products will have an adverse influence on catalyst life. 

Hydroxylamines ordinarily do not accumulate in the reduction of aromatic nitro compounds for, with some exceptions, most systems in competition will reduce the hydroxylamine function preferentially. Nonetheless, systems have been found that afford the intermediate aromatic hydroxylamine in excellent yield. With hydrogen gas as a reductant and platinum-on-carbon or -on-alumina and about I wt % of DMSO based on nitro compound as a modifier, aromatic hydroxylamines can be formed in 90% yield under mild conditions. The reduction slows markedly after absorption of the second mole of hydrogen and should be stopped at this stage (80). 

Formation of azo-type products might be troublesome. These by-products, arising from reduction of aromatic nitro compounds, usually are assumed to be derived from the coupling of intermediate nitroso and hydroxylamine compounds. The coupling problem is accentuated in reduction of nitroso compounds because of much higher concentrations. It can be alleviated by dropwise addition of the substrate to the hydrogenation and use of acidic media. 

INDIUM/AMMONIUM CHLORIDE-MEDIATED SELECTIVE REDUCTION OF AROMATIC NITRO COMPOUNDS ETHYL 4-... 

Cell-free supernatants may mediate reductions. The reduction of aromatic nitro compounds by SH was mediated by the hltrate from a strain of Streptomyces sp. that is known to synthesize 2-amino-3-carboxy-5-hydroxybenzo-l,4-quinone (cinnaquinone)... 

Reduction of aromatic nitro compounds by sulfide catalyzed by extracellular compounds excreted into the medium during growth of Streptomyces griseoflavus (Glaus et al. 1992). 

Wang, H., Yan, J., Chang, W., and Zhang, Z. (2009) Practical synthesis of aromatic amines by photocatalytic reduction of aromatic nitro compounds on nanoparticles N-doped Ti02. Catalysis Communications, 10 (6), 989-994. 

Electrochemically generated nickel is very selective for the reduction of aromatic nitro compounds into anilines, in which alkenyl, alkynyl, halo, cyano, formyl, and benzyloxy groups are not affected.84 Sodium sulfide has been used for the selective reduction of aromatic nitro group in the presence of aliphatic nitro groups (Eq. 6.44).85... 

The reduction of aromatic nitro compounds to amino derivatives and cyclizations to various heterocyclic compounds are presented in Chapter 9. Recent advances are presented here. Reaction of 2-nitrobenzaldehyde with vinyl carbonyl compounds in the presence of 1,4-diazbi-cyclo[2.2.2]octane affords Baylis-Hillman products, the catalytic reduction of which results in direct cyclization to quinoline derivatives (Eq. 10.78).134... 

Iron(II) sulphate is a by-product in many industrial processes, such as the manufacture of titanium dioxide, the pickling of steel sheet before galvanising and the reduction of aromatic nitro compounds to amines using iron catalysts. Conversion of waste iron (II) salts to usable iron oxide pigments, where the quality requirements are not too stringent, is therefore a useful proposition, since it uses up chemicals that would otherwise be regarded as waste products. 

The reduction of aromatic nitro-compounds is of exceptionally great interest, not only scientifically, hut also technically. The conversion of the hydrocarbons of coal tar into useful products began with the discovery of the nitration process the conversion, on the technical scale, of the nitro-group of nitrobenzene into the amino-group gave aniline, the starting material for the preparation of innumerable dyes and pharmaceutical products to aniline were added the homologous toluidines, xylidines, naphthylamines, and so on. 

The mechanism of the global 4-electron electrochemical reduction of aromatic nitro compounds to hydroxylamines in aqueous medium shown in reaction 37 was investigated by polarography and cyclic voltametry. The nitro group is converted first to a dihy-droxylamine, that on dehydration yields a nitroso group the latter is further reduced to a... 

A number of authors measured the influence of ring substituents on the rate of catalytic reduction of aromatic nitro compounds by hydrogen (5-7,114,128). The series have been composed in such a way as to allow the Hammett correlations, but, with a single exception, scatter diagrams resulted. The successful case by Rflzicka and Santrochova 128) (series 102, 12 points, slopes for three different platinum catalysts 0.24, 0.34, and 0.92, respectively) differs from the others in the use of platinum catalysts, whereas the other authors worked with rhodium (4,5), palladium (5,114), ruthenium... 

Ferrous sulfate is a gentle reducing agent. It is applied in aqueous solutions mainly for reduction of aromatic nitro compounds containing other reducible functions such as aldehyde groups which remain intact [218]. 

A special use of sodium arsenite (applied in aqueous alkaline solutions) is partial reduction of trigeminal halides to geminal halides [220] and reduction of aromatic nitro compounds to azoxy compounds [221]. 

Enzymatic reduction of aromatic nitro compounds such as 79 into hydroxylamines (equation 56) by plant cells has been recently reported. ... 

Lauwiner, M. Rys, P. Wissmann, J. (1998) Reduction of aromatic nitro compounds with hydrogene hydrate in the presence of an iron oxide hydroxide catalyst. I. The reduction of monosubstituted nitrobenyenes with hydrazine hydrate in the presence of ferrihydrite. 

Pradhan N, Pal A, Pal T (2001) Catalytic Reduction of Aromatic Nitro Compounds by Coinage Metal Nanoparticles. Langmuir 17 1800-1802... 

Further complications of the reduction of aromatic nitro compounds are the possibility of complete reduction to aromatic amines (which may condense with nitroso compounds to give the desired azo compounds), reduction of azo compounds to the corresponding hydrazo compounds, followed by a benzidine (or semidine) rearrangement. It is clear, therefore, that the level of reducing agent used and other reaction conditions are quite critical. 

Reduction of aromatic nitro compounds with carbon monoxide [119] (Eq. 60). 

Historically this reaction developed from the assumption that the formation of azoxy compounds by the reduction of aromatic nitro compounds probably involved the intermediate formation of C-nitroso compounds and hydroxylamines. In the all-aliphatic series, this reaction appears to be quite general. Symmetrically and unsymmetrically substituted azoxy compounds have been prepared by it, the only major problems being the usual ones of developing procedures that afford good yields and of determining the exact position of the azoxy oxygen in unsymmetrically substituted products. 

The bimolecular reduction of aromatic nitro compounds, depending on reaction conditions, may proceed by way of azoxy and azo compounds to 1,2-diarylhydrazines (also referred to as hydrazo compounds). This may be... 

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