Reduction of a nitro

Reduction of a nitro compound to a hydroxylamine. Dissolve 0-5 g. of the compound in 10 ml. of 50 per cent, alcohol, add 0-5 g. of solid ammonium chloride and about 0 5 g. of zinc powder. Heat to boiling and allow the ensuing chemical reaction to proceed for 5 minutes. Filter from the excess of zinc powder and test the filtrate with ToUen s reagent see Section III,70,(i). An immediate black or grey precipitate or a silver mirror indicates the presence of a hydroxylamine formed by the reduction of the nitro compound. Alternatively, warm the filtrate with Fehling s solution a hydroxylamine will precipitate red cuprous oxide. (A blank test should be performed with the original compound.)... 

Reduction of a nitro compound to a primary amine. In a 50 ml. round-bottomed or conical flask fitted with a reflux condenser, place 1 g. of the nitro compound and 2 g. of granulated tin. Measure out 10 ml. of concentrated hydrochloric acid and add it in three equal portions to the mixtiue shake thoroughly after each addition. When the vigorous reaction subsides, heat under reflux on a water bath until the nitro compound has completely reacted (20-30 minutes). Shake the reaction mixture from time to time if the nitro compound appears to be very insoluble, add 5 ml. of alcohol. Cool the reaction mixture, and add 20-40 per cent, sodium hydroxide solution imtil the precipitate of tin hydroxide dissolves. Extract the resulting amine from the cooled solution with ether, and remove the ether by distillation. Examine the residue with regard to its solubility in 5 per cent, hydrochloric acid and its reaction with acetyl chloride or benzene-sulphonyl chloride. 

Controlled-potential coulometry also can be applied to the quantitative analysis of organic compounds, although the number of applications is significantly less than that for inorganic analytes. One example is the six-electron reduction of a nitro group, -NO2, to a primary amine, -NH2, at a mercury electrode. Solutions of picric acid, for instance, can be analyzed by reducing to triaminophenol. 

Sodium Bisulfite. Sodium bisulfite [7631-90-5] NaHSO, is occasionally used to perform simultaneous reduction of a nitro group to an amine and the addition of a sulfonic acid group. For example, 4-amino-3-hydroxyl-l-naphthalenesulfonic acid [116-63-2] C qH NO S, is manufactured from 2-naphthol in a process which uses sodium bisulfite (59). The process involves nitrosation of 2-naphthol in aqueous medium, followed by addition of sodium bisulfite and acidification with sulfuric acid. 

A series of amides has been prepared as protective groups that are cleaved by intramolecular cyclization after activation, by reduction of a nitro group, or by activation by other chemical means. These groups have not found much use since the first edition of this volume and are therefore only listed for completeness. The concept is generalized in the following scheme ... 

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. 

Aromatic nitro and nitroso compounds are easily reduced at carbon and mercury electrodes. Other nitro compounds such as nitrate esters, nitramines, and nitrosamines are also typically easily reduced. The complete reduction of a nitro compound consists of three two-electron steps (nitro-nitroso-hydroxylamine-amine). Since most organic oxidations are only two-electron processes, higher sensitivity is typically found for nitro compounds. Several LCEC based determination of nitro compounds have been reported... 

The first compound of Equation 36 is not made by the condensation procedure, but by the chemical reduction of a nitro group in parathion. Some compounds are rather difficult to obtain by the general method. However, the next three compounds shown here were prepared by this method. 

Nitrophenylpyruvic acid was reduced to oxindole using iron pin-dust-ferrous sulfate in water. The iron oxide-iron residues, after filtering and washing with chloroform, rapidly heated in contact with air and shattered the Buchner funnel [1], Previously, rapid heating effects had been observed on sucking air through the iron oxide residues from hot filtration of aqueous liquor from reduction of a nitro compound with reduced iron powder [2],... 

In preparation for the reduction of a nitro compound, the tetrahydroborate solution is added to an aqueous supension of palladium-on-charcoal catalyst. The reversed addition of dry catalyst to the tetrahydroborate solution may cause ignition of liberated hydrogen. 

Pd(0)-catalyzed substitution reaction, a novel, mild reduction of a-nitro ester to an amino acid ester with TiCl3, and an improved procedure for uracil ring formation. 

Reduction of a nitro compound to the corresponding naphthylamine proceeds exactly as in the benzene series. A batch process using iron and hydrochloric acid is traditional but has been somewhat superseded by catalytic hydrogenation. 

REDUCTION OF A NITRO COMPOUND TO AN AMINE (a) Aniline from Nitrobenzene1... 

There continue to be a few examples reported where rearrangement has been used synthetically to develop new products sometimes important in the industrial world. Monomers for polyamides and polyimides (which are used for making moisture sensitive films, fibres and mouldings) have been synthesized24 by the reduction of a nitro compound, followed by a benzidine rearrangement of the resulting hydrazobenzene derivative as outlined in Scheme 5. 

Preferential reduction of a nitro group in the presence of a carbonyl group in 4-nitroacetophenone ISD, intramolecular rearrangements of o-nitro-benzanilides 32) intramolecular cyclizations of o-nitro-ferf-anilines to benzimidazol-1-oxides 153,154) cyclizations of acylated 2-nitrodiphenylamines to phenazine-l-oxides i ), intramolecular additions of nitro groups to double bonds 156) remarkably ef-... 

Reduction of nitro esters to amino esters is easy, since most of the reagents used for the reduction of a nitro group to an amino group do not attack the ester group. Ethyl 2-chloro-4-nitrobenzoate was quantitatively hydrogenated to either ethyl 2-chloro-4-aminobenzoate or 4-aminobenzoate over palladium [7057]. 

Iron and acetic or dilute hydrochloric acid can be safely used for the reduction of nitro group to an amino group in nitro esters. The problem arises when a nitro ester is to be reduced to a nitro alcohol. Nitro groups are not inert toward the best reagents for the reduction of esters to alcohols, complex hydrides. However the rate of reduction of a nitro group by lithium... 

Oxidation of an alkylated benzene (making an aryl carboxylic acid) is a method of converting an ortho-para activator into a meta director. The reduction of a nitro group to make an aryl amine is a way of changing a meta director into an ortho-para activator. 

In some cases in which the Caro s acid oxidation of amines was not satisfactory, the corresponding hydroxylamines have been oxidized with acidified dichromate solutions [42], Both aliphatic and aromatic nitroso compounds have been prepared by this method [17, 42, 82, 90]. Frequently the reaction mixture from the reduction of a nitro compound is treated directly with the oxidizing medium without the isolation of the intermediate hydroxylamine. The method has been called the nitro reduction oxidation technique, [82] a terminology we cannot condone. 

Four-membered rings are not obtained during reduction of a-nitro-/ -keto alkenes the oxygen of the hydroxylamine intermediate attacks the electrophilic center1,71 with formation of isoxazole derivatives. 

The reduction of a nitro compound to an amine requires six equivalents of reducing agent ... 

Vitamin B12 also catalyzes the reduction of a nitro group by NaBH+, but less efficiently. 

The efficiency of the reduction generally increases when the concentration of the nitro compound decreases. The photoredox reactions are halted when photons are absorbed by the nitro compounds. The concentration limit of this reaction is dependent on the extinction coefficient of a nitro compound in the UV region. These limits are 5 x 10-3 M for 6-nitrocoumarin and 5 x 10-2 M for p-nitrobenzaldehyde (Mahdavi et al., 1993). Complete reduction of a nitro compound would require six protons and would leave six electron holes behind. The oxidation of an alcohol and the reduction of a nitro compound are presented in Figure 9.9. 

The analogy between the behaviour of these diketonate complexes and benzene derivatives is indeed remarkable, and reaction sequences very reminiscent of those observed in organic aromatic chemistry are common. In Fig. 5-9, the reduction of a nitro to an amino derivative is illustrated, a conversion reminiscent of the reduction of nitrobenzene to aniline. It is usually necessary to use kinetically inert cP or d6 metal complexes in sequences of this type. 

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