Of nitro compounds to amines

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). 

In the reduction of nitro compounds to amines, several of the iatermediate species are stable and under the right conditions, it is possible to stop the reduction at these iatermediate stages and isolate the products (see Figure 1, where R = CgH ). Nitrosoben2ene [586-96-9] C H NO, can be obtained by electrochemical reduction of nitrobenzene [98-95-3]. Phenylhydroxylamine, C H NHOH, is obtained when nitrobenzene reacts with ziac dust and calcium chloride ia an alcohoHc solution. When a similar reaction is carried out with iron or ziac ia an acidic solution, aniline is the reduction product. Hydrazobenzene [122-66-7] formed when nitrobenzene reacts with ziac dust ia an alkaline solution. Azoxybenzene [495-48-7], C22H2QN2O, is... 

Hydrogen gas can be replaced by ammonium formate for the reduction of nitro compounds to amines. The ammonium formate method is efficient, and the rapid workup procedure by simple filtratkin makes it widely used for converting the NO to the NH. ° For example, ct-nitro esters are reduced to ct-amino esters in excellent yields on treatment v/ith HCO NH and PdAZ in methanol. ... 

The hydrogenation in the presence of Pd/C is also effective for the conversion of nitro compounds to amines.94 The Michael addition of nitromethane to 2-alkenoic esters followed by catalytic hydrogenation using 10% Pd/C in acetic acid and hydrolysis is a convenient method for the preparation of 3-alkyl-4-aminobutanoic acids, which are important y-amino acids for biological study (Eq. 6.48).94b The reduction can be carried out at room temperature and atmospheric pressure. 

All of these substances can be reduced to benzenamine with tin and hydrochloric acid. As a result, each could be, but not necessarily is, an intermediate in the reduction of nitro compounds to amines. Formation of the bimolecular reduction products is the result of base-induced reactions between nitroso compounds and azanols or amines and possibly further reduction of the initially produced substances (see Exercise 24-18). 

Ready conversion of nitro compounds to amines further extends the applicability of the deamination process. For example, the nitro group may be introduced into an aromatic nucleus for the purpose of closing a position to other groups in subsequent steps of a synthetic sequence, and, finally, the nitro group is replaced by hydrogen. This blocking effect is utilized in the preparation of 2-chlororesorcinol, which cannot be obtained by direct chlorination of resorcinol.187... 

Reduction of nitro compounds to amines is an essential step in what is probably the most important synthetic route in aromatic chemistry. Nitro compounds are readily prepared by direct nitration when a mixture of o- and p-isomers is obtained, it can generally be separated to yield the pure isomers. The primary aromatic amines obtained by the reduction of these nitro compounds are readily converted into diazonium salts the diazonium group, in turn, can be replaced by a large number of other groups (Sec. 23.11). In most cases this sequence is th best method of introducing these other groups into the aromatic ring. In addition, diazonium salts can be used to prepare the extremely important class of compounds, the azo dyes. 

B) Reduction of Nitro Compounds to Amines. Place 0.5 ml of nitromethane or 1-nitropropane in a test tube immersed in cold water add 2 ml of concentrated hydrochloric acid and then a piece of granulated tin. When the reduction is complete, add with cooling 5 ml of 6 N sodium hydroxide solution. Note the strong odor of alkylamine. Devise a test for confirmation. 

Sym. disulfides from halides with simultaneous reduction of nitro compounds to amines... 

Scheme 8.60. Reduction of nitro compounds to amines with alumina-supported hydrazine.

Nitro Compounds. - Catalytic hydrogenation of nitro compounds to amines takes place readily at room temperature and atmospheric pressure. The mechanism proceeds via the nitroso and hydroxylamine stages and azo, azoxy, and hydrazo compounds may also be produced. ... 

Reduction of Nitriles and of Nitro Compounds to Amines Nitro compounds can be reduced over metallic catalysts at relatively low temperatures and pressures. However, for several reasons, it is more desirable to carry out this reduction over nickel sulfide catalysts. The feedstock does not have to be freed of sulfur compounds. A high hydrogen pressure can be used, which makes continuously operating units more eflicient and favors the formation of primary amines which are usually the desired products. 

Reduction of nitro compounds to amines is a synthetically important reaction (98) and is practiced since the birth of modern chemical industry—many aromatic amines are key intermediates in production of dyes and pesticides. However, the stoichiometric reductions using iron or alkali metal hydrogen sulfides or catalytic hydrogenations with heterogeneous catalysts leave room for improvements in selectivity, especially with reference to halonitro-derivatives. There are many homogeneous catalysts such as the rhodium carbonyls in the presence of amines or chelating diamines, or [Rus(CO)i2] in basic amine solutions that are... 

In this paragraph, several stoichiometric and catalytic systems for the reduction of nitro compounds to amines are described. Before discussing the individual systems, some general characteristics must be evidenced. 

Ru(PPh3)3Cl2 is a good catalyst for the phase-transfer-catalysed reduction of nitro compounds to amines by synthesis gas (1 1 CO/H2, note that water is also present in the reaction mixture) at room temperature and atmospheric CO pressure [34] (eq. 7) ... 

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