Reduction of aromatic nitro groups

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... 

Reductions with zinc are carried out in aqueous [160 as well as anhydrous solvents [163 and at different pHs of the medium. The choice of the reaction conditions is very important since entirely different results may be obtained under different conditions. While reduction of aromatic nitro groups in alkali hydroxides or aqueous ammonia gives hydrazo compounds, reduction in aqueous ammonium chloride gives hydroxylamines, and reduction in acidic medium amines (p. 73). Of organic solvents the most efficient seem to be dimethyl formamide [164 and acetic anhydride [755]. However, alcohols have... 

Reduction of aromatic nitro group takes preference to the reduction of the aromatic ring. Under certain conditions, however, even the benzene ring was reduced. Hydrogenation of nitrobenzene over platinum oxide or rhodium-platinum oxide in ethanol yielded aniline while in acetic acid cyclohexylamine was produced [55]. Heating of nitrobenzene with formic acid in the presence of copper at 200° gave a 100% yield of aniline, whereas similar treatment in the presence of nickel afforded 67% of cyclohexylamine [71]. 

A very reliable reagent for reductions of aromatic nitro groups in the presence of sensitive functions is iron, which does not affect carbon-carbon double bonds [555]. 

The reduction of aromatic nitro groups by use of electro-generated titanium(III) has also been investigated very intensively, especially in India. Thus, aniline derivatives are generated in high yield Evidently this method has some... 

In the following we will try to illustrate these general points by discussing two specific types of redox reactions the reduction of aromatic nitro groups (Eq. 14-9) and the reductive dehalogenation of polyhalogenated Cr and C2-compounds (Eqs. 14-6 to 14-8). These two cases represent two very different types of reactions. In the first case, the transfer of the first electron is reversible, whereas in the second case, it is typically irreversible and involves the breaking of a bond. In the latter case, therefore, one speaks of a dissociative electron transfer. Furthermore, compounds... 

A combination of iron(III) salts with solid-supported hydrazine hydrate (preabsorbed on AI2O3) were successfully used in reductions of aromatic nitro groups (Scheme 4.33). The nature of the solid support plays a crucial role in this reaction and alumina was found to be most effective. In the absence of a solid support, the reaction... 

Aromatic amines are readily prepared by the reduction of aromatic nitro groups by Fe/HCl or Sn/HCl or by catalytic hydrogenation. 

Reduction of aromatic nitro groups occurs in three steps, via nitroso and hydroxylamine intermediates, to the amine. The amine can go on to form polymeric residues by a mechanism analogous to that for oxidative coupling of phenols, as in Equation 2. Abiotic nitro reduction is well documented for pesticides that contain aromatic nitro groups, such as the phosphorothioate esters methyl and ethyl parathion (22, 30-33). 

Aliphatic nitro compounds are hydrogenated under the same conditions used for the reduction of aromatic nitro groups. They follow the same reaction path as illustrated in Scheme 19.1 for aromatic nitro compounds, but they are hydrogenated somewhat less readily than the aromatic species (Eqn. 19.21). 5 Double bonds are hydrogenated in preference to the aliphatic nitro group but not carbonyl or oximino groups. 6> ... 

Zachariah PK, Juchau MR. 1974. The role of gut flora in the reduction of aromatic nitro-groups. Drug Metab Dispos 2 74-78. 

Reduction of aromatic nitro groups using triethylammonium formate, catalyzed by pal-ladium-on-carbon or a soluble triaryphosphine-palladium acetate catalyst is compatible with ester or amide functions, leading to a-amino esters . The nitro group of the pyra-none 2 is selectively reduced, without hydrogenolysis of the benzyl ether linkage in the presence of finely divided Ni ° ... 

Reduction of aromatic nitro groups with formamidinesulfinic acid Chatteijie, Nithiananda Minar, Arlene Clarke, Donald D. 

Because the reduction of aromatic nitro groups is such a facile process, reductive transformation of chemicals containing this moiety is often the dominant pathway for their transformation in the environment. For example, the reduction of methyl parathion, which is representative of the nitro-containing organophosphorus insecticides, to amino methyl parathion has been observed in anaerobic sediments (Wolfe et al., 1986) and flooded soils (Wahid and Sethunathan, 1979 Wahid et al., 1980 Adhya et al., 1981a and 1981b Gambrell et al., 1984), with half-lives on the order of minutes to hours (Equation 3.22). 

Procedures were proposed for the reduction of aromatic nitro groups to amines. Sodium dithionitei78 and a combination of sulfur and hydrazine on activated carboni79 are reported to provide anilines in good to excellent yields. From aliphatic nitro compounds (Eq. 66), primary amines could be obtained with "nickel boride", prepared from nickel chloride and sodium borohydride.i ... 

Reductive reactions are not generally of common occurrence in plants and usually are insufficiently rapid to play a significant role in pesticide detoxification and selectivity. A reaction which has been recorded, however, is the reduction of aromatic nitro groups to the corresponding anilines, and the observed reduction of botran (2,6-dichloro-4-nitroaniline) by axenic callus cultures of soybean demonstrated the ability of plant tissue per se to mediate such biotransformations. While such reactions appear not to occur extensively in higher plants, the reductive deamination (Figure 10.3) of the substituted triazinone metribuzin (3) to 4 represents a major detoxification mechanism which may account for the tolerance of soybean cultivars to metribuzin. Thus, deamination in leaves of tolerant Bragg ... 

Previously, reduction of aromatic nitro groups has been thought to increase the resistance of the molecule to biodegradation. Recent work (3, 34) has shown that reduction of the nitro group to the amine level can result in productive metabolism under anaerobic conditions. Complete reduction of nitro groups has been widely reported to occur in aerobic bacteria (20, 40). However, the amines produced by such reactions seem to be dead end metabolites under aerobic conditions. 

The enzymatic reduction of the nitro group involves the stepwise addition of six reducing equivalents potentially derived from reduced pyridine nucleotides (Fig. 8). The first reaction yields a nitroso derivative which is subsequently reduced to a hydroxylamine the hydroxylamino compound is then reduced to the amine. In most systems studied to date (Cemiglia and Somerville, this volume) a single nitroreductase enzyme is responsible for all three reactions and there is little or no accumulation of the intermediates. However, reduction of nitro compounds does not seem to be the physiological function of the enzymes that have been reported to carry out these reactions. Diaphorases (23), ferredoxin-NADPH reductase (33), and a variety of other enzymes from procaryotes and eucaryotes have been shown to catalyze the fortuitous reduction of aromatic nitro groups. 

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