Reduction of Nitro- to Amino-groups

Reduction of Nitro- to Amino-groups. - Sulphide catalysts continue to find application in selective hydrogenation of nitro-groups. Aromatic nitro-groups in the presence of acetylenes were selectively hydrogenated (373 K, 25-70 atm, in isopropanol) to amino-groups over cobalt polysulphide and RUS2 catalysts, for example (3-nitrophenyl)acetylene to (3-aminophenyl)acetylene in 75-85% yield.  

Bhinde, S, Shih, R. Zawadski, J. R. Katzer, and H. Kwart, in Proceedings Climax Third International Conference on the Chemistry and Uses of Molybdenum , ed. H. F. Barry and P. C. H. Mitchell, Climax Molybdenum Co., Ann Arbor, 1980, p. 184. 

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In both cases the minimum donor - acceptor molar ratio demanded for the reduction of nitro- to amino group equals 3. 

The few direct toxicity comparisons using nitro-substituted phenols and their reduced metabolites indicate that the relationship between reduction of nitro to amino groups, and toxicity varies with the degree of nitration of the parent compound and the test species. The reduction of picric acid to picramic acid (2-A-4,6-DNP) and of 4-NP to 4-AP promoted an order of magnitude toxicity increase in lethal and sub-lethal assessments with several marine and freshwater invertebrates, fish, and algae [12,29,59] (Table 4.5). The reduction of 2,4-DNP to 4-A-2-NP, however, decreased toxicity to P. promelas by 2.5-fold [50,61],... 

Deamination with reduction of nitro to amino groups... 

Substituents attached to aryl groups on imidazole or its benzo derivatives have their normal individual reactivities, e.g, reduction of nitro to amino, diazotization of amino, etc., although there may be some modification of these properties because of the particular environment. 

The Michael addition of nitro compounds to ct,fi-unsatiirated ketones or esters followed by reduction of the nitro to amino group is useful for the preparation of various heterocycles This is presented in Chapter 10 (Symhesis ofHatarocyclas). 

Meyer (17) in the following year then expressed the view that the products of the action of nitrous acid on the ketones were not true nitroso compounds (4) but isomeric oximes (5), and he considered their reduction to be analogous to the conversion of a nitro to amino group, rather than that of ketone to pinacol. Thereafter the Treadwell formulation of pyrazines was abandoned. 

It is difficult to imagine a mechanism generally adaptable to so different catalysts. The easier route should be the reduction of the nitro to amino group, followed by ring closure. However, no water or alcohol was present in the reaction mixture. Moreover, as far as we know, Pt(PPh3)4 has no precedents as catalyst for the carbonylation of organic nitro compounds. 

To the best of our knowledge, this is the first report of a dealkylation of tliis type mediated by a transition metal cluster carbonyl. The formation of this hydride could explain in part the large amount of amine 57 formed during the catalytic reactions. This compound has in fact been considered a key intermediate in the catalytic hydrogenation of nitrobenzene to aniline [97]. However, as has been discussed in Chapters 4 and 6, the participation of hydride derivatives in this type of reduction of the nitro to amino group is doubtful. 

The classic approach to A -acetylated para-aminophenols comprises the nitration of phenol, reduction of the nitro to amino group and A -acetylation. The acetylation step proceeds with limited chemoselectivity, however, accompanied by the formation of A, A -diacetylated and 0-acetylated products. The proposed retrosynthesis represents an elegant solution retra-Beckmann to oxime as the key step, followed by FGI to ketone and retro-Friedel-Crafts disconnection to phenol (Scheme 8.2). 

Aromatic amines are the reduced salt of nitro aromatics or azo compounds. The electron donating amino groups formed from the reduction of nitro and azo groups are estimated to carriage a serious problem to further reductive bio transformations... 

Recent examples on substituted derivatives include the conversion of 4-nitroaniline into p-phenylendiamine by CdS visible light photo-catalysis. Selective reduction of the nitro group in 2 to an amino group has been obtained by irradiation in the presence of Ag nanoparticles of 2,4-dinitro (and 2-nitro-4-chloro)benzenethiol. The nitro to amino group selective reduction in observed also with 2-nitrovinylbenzene preserving the C=C double bond. ... 

Azo-compounds can be obtained by reduction of nitro-compounds, or by oxidation of hydrazo-compounds. They are usually prepared, however, by reacting a phenol or amine with a diazonium salt. The coupling usually takes place in the position para to the hydroxyl or amino group, but if this position is occupied it goes to the ortho position, e.g. 

Amino groups are formed by reduction of nitro groups in aryl substituents and behave normally (62JCS1671), but when attached directly to the pyridopyridazine ring they may be removed by acid hydrolysis or treatment with nitrous acid, or replaced by hydrazine. 

Nitro groups have been reduced to amino groups, whilst amino groups in the 3- and 6-positions of pyrido[2,3-f ]pyrazines and in the 5-position of the [3,4-f ] isomers have been hydrolyzed to the corresponding hydroxy derivatives with alkali. Protected amino groups have been liberated by hydrolysis or reduction in deazapteridine syntheses. 

An easy approach to obtain amino-substituted phthalocyanines is the reduction of nitro groups, which are easily introduced into the macrocycle by condensation of the respective phthalonitrile. 

Fig. 21 Reaction scheme for the detection of aromatics, by means of the reaction sequence, nitration, reduction, diazotization and coupling to an azo dye, and of aliphatic nitro compounds by detection of the primary amino group produced on reduction.

The degradation of 2,4,6-trinitrotoluene under aerobic conditions is strictly dependent on the reduction of one or more nitro groups to amino groups before dioxygenation (Fiorella and Spain 1997 Johnson et al. 2001). 

Amino-2-methoxyphenyl)perhydropyrido[l,2-tf]pyrazine was prepared from a 2-(5-nitro-2-methoxyphenyl)-3-one derivative by catalytic hydrogenation over Pd/C catalyst, followed by the reduction of the 3-oxo group by treatment with BH3-THF complex <1999WO99/042465>. A nitro group was reduced to an amino group in 2-[4-(3-nitrophenyl)piperazin-l-yl]butyl]perhydropyrido[l,2-tf]pyrazine-l,4-dione <2001JME186>, in 8-hydroxy-... 

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