Affecting Nitro Groups

2-Nitro-, 2,8-dinitro-, and 4,8-dinitrophenoxatellurins were reduced to the corresponding aminophenoxatellurins with tin in concentrated hydrochloric acid.  

2-AminophenoxatelIurin A mixture of 2.0 g (5.9 mmol) of 2-nitrophenoxatellurin and a large excess of tin and concentrated hydrochloric acid is heated on a boihng water bath for several hours until the yellow color of the nitrophenoxatellurin has disappeared. The mixture is filtered, the filtrate is treated with cold aqueous sodium hydroxide solution, the solid is shaken with aqueous sodium hydroxide solution, the residual solids are collected, combined, and extracted with chloroform in a Soxhlet apparatus. The chloroform is 

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Brown and Subba Rao have found that sodium borohydride reduces nitriles to amines, but does not affect nitro groups or amides. 

A nitro group in the 4-position markedly increases the instability of the isoxazole ring in alkaline medium. This effect is clearly demonstrated by 3,5-dime thy 1-4-nitroisoxazole. Whereas 3,5-dimethyl-isoxazole is not affected by alkali, its 4-nitro-derivative (134) is cleaved by 2% sodium hydroxide. The structure of the product was proved by its conversion into a triazole (135) with phenyl diazonium chloride, according to the original authors. ... 

Electrochemically generated nickel is very selective for the reduction of ai compounds into anilines, in which alkenyl, alkyhyl, halo, cytino, formyl, ind benzyloxy groups are not affected. Sodium snlfide has been used for the selective reduction of at group in the presence of aliphatic nitro groups (Tq. 6.44. ... 

In nitrobenzene the nitro group has a large electron affinity, and accordingly draws electrons away from the ring. The resonance effect works in the same direction, and, as a result, all positions have a deficiency of electrons. The meta positions are least affected, and the substitution takes place there with difficulty. In aniline, the inductive effect and the resonance effect oppose each other, but the latter wins out, and very easy o-p substitution takes place. 

The stereospecific base-cleavage of the trimethylsilyl group in 1,3-dithiane 1-oxides 499 enables to obtain the specifically deuteriated products 500 (equation 303), A nitro group in y-nitroalkyl sulphoxides 501 (obtained by the Michael addition of nitroalkanes to a, j8-unsaturated sulphoxides) is replaced by hydrogen by means of tributyltin hydride (equation 304). This reagent does not affect the sulphinyl function. The overall procedure provides an efficient method for the conjugate addition of alkyl groups to a, -unsaturated sulphoxides . ... 

Subsequently, these authors have also studied the effect of polar factors on the sulfenate-sulfoxide equilibrium and obtained similar results to those reported by Braverman and coworkers . For example, reaction of 2,4-dinitrobenzenesulfenyl chloride with lithium allyl-a-dj alcoholate gives only (or perhaps mainly ) allyl-a-d2 2,4-dinitrobenzenesulfenate, whereas the corresponding reaction with 4-nitrobenzenesul-fenyl chloride results in complete ( > 99%) rearrangement to the sulfoxide. However, when a single nitro group is located in the ortho position, the ratio (K) of sulfenate to sulfoxide approaches unity. This ratio is also affected by the polarity of the solvent and changes from 1.43 in CCI4 to 0.39 in chloroform, consistent with the results described above for the equilibrium shown in equation 9. 

These reaction conditions also permit the chemoselective quantitative reduction of benzaldehyde to benzyl alcohol without any concomitant reduction of either acetophenone or 3,3-dimethylbutan-2-one present in the same reaction mixture.83 Additionally, this useful method permits the reduction of aldehyde functions in polyfunctional compounds without affecting amide, anhydride, eth-ylenic, bromo, chloro, or nitro groups.79,80,319... 

The traditional technique of reducing nitro compounds with iron powder in dilute acid (Bechamps-Brimmeyr reduction) continues to be used for nitro compounds that are adversely affected by the catalytic reduction method with hydrogen. The list of examples includes aromatic nitro compounds carrying halogen substituents, especially if these are attached in ortho or para position to the nitro group. The solution containing only a small amount of acid (such as acetic acid) is almost neutral and allows iron to precipitate as Fe304. 

Selective reduction (e.g., partial reduction of one of two nitro groups) is carried out with an alkali sulfide, such as sodium hydrogen sulfide NaHS ( sodium sulfhy-drate ) or sodium sulfide Na2S, in an aqueous or alcoholic solution. Azo groups are not affected by this method. The reaction converts sodium hydrogen sulfide or sodium sulfide mainly to sodium thiosulfate. 

Some further light on the behaviour of the nitro group as an orf/ o-subsliUicnl in affecting the strength of benzoic acid can be obtained by correlation analysis employing the extended Hammett equation (Section n.B) in the form of equation 14 ... 

As discussed above, the nitro groups of tetranitromethane and trinitromethyl compounds are susceptible to nucleophilic attack. Both potassium iodide and alkaline hydrogen peroxide affect the reductive denitration of trinitromethyl groups to em-nitronitronates 1,1,1-trinitroethane (33) is quantitatively reduced to potassium 1,1-dinitroethane (24) on treatment with alkaline hydrogen peroxide. Nucleophiles such as potassium fluoride in DMF can displace nitrite anion from tetranitromethane. Various nucleophiles, including azide, chloride, fluoride and ethoxide have been used to displace one of the nitro groups from fluorotrinitromethane. 

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]. 

Neither aromatic halogens [232,602] nor nitro groups were affected during the reductions of the azido group [232, 247, 602]. a-Iodo azides gave, on reduction, aziridines or alkenes depending on the substituents and on the reagents used [603]. 

Reductive cleavage of disulfides is very easy and can be accomplished without affecting some other readily reducible groups such as nitro groups. 

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