Hydrazobenzene nitrobenzene

Reduction of nitrobenzene in methyl or ethyl alcoholic sodium hydroxide solution with zinc powder leads to azobenzene or hydrazobenzene according to the proportion of zinc powder employed ... 

The reduction of the nitro group to yield aniline is the most commercially important reaction of nitrobenzene. Usually the reaction is carried out by the catalytic hydrogenation of nitrobenzene, either in the gas phase or in solution, or by using iron borings and dilute hydrochloric acid (the Bechamp process). Depending on the conditions, the reduction of nitrobenzene can lead to a variety of products. The series of reduction products is shown in Figure 1 (see Amines byreduction). Nitrosobenzene, /V-pbenylbydroxylamine, and aniline are primary reduction products. Azoxybenzene is formed by the condensation of nitrosobenzene and /V-pbenylbydroxylamine in alkaline solutions, and azoxybenzene can be reduced to form azobenzene and hydrazobenzene. The reduction products of nitrobenzene under various conditions ate given in Table 2. 

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... 

Diaminodiphenyl derivatives can be obtained from appropriately substituted nitrobenzenes by a rather dated process of alkaline reduction with zinc powder/ sodium hydroxide solution, which affords hydrazobenzene. A more recent method uses a catalytic reduction process with hydrogen and specifically deactivated catalysts of precious metals. Subsequent acid-catalyzed rearrangement with hydrochloric acid yields the hydrochloride of the target diamine ... 

Since azoxybenzene is attacked by more powerful reducing agents, e.g. zinc dust and sodium hydroxide solution or ammonia, the use of such agents converts nitrobenzene to azobenzene and hydrazobenzene, by passing at once beyond the azoxybenzene stage. The three reduction products with paired " nitrogen atoms, therefore, stand in very close genetic relation to each other. 

Azoxybenzene (1 g.) is dissolved in 5 c.c. of alcohol, the solution is heated to boiling, and 3 c.c. of 50 per cent sodium hydroxide solution and 2-3 g. of zinc dust are added with shaking. At first the mixture becomes red, because of the formation of azobenzene, but on more prolonged boiling a colourless solution is obtained just as in the reduction of nitrobenzene. When this stage has been reached, the mixture is filtered with suction through a small Buchner funnel and the hydrazobenzene is finally isolated in the manner described on p. 183 et seq. 

The reduction of nitrobenzene may also be accomplished by triplet excited pyrochlorophyll Comparison of the quantum 5delds of such photoreductions by hydrazobenzene in ethanol-pyridine solutions with the polarographic quarter... 

Direct preparation of azo compounds in good yields is accomplished by treatment of nitro compounds with lithium aluminum hydride [576], with magnesium aluminum hydride [577], with sodium bis(2-methoxy ethoxy)aluminum hydride [575], with silicon in alcoholic alkali [331] or with zinc in strongly alkaline medium [578], Hydrazobenzene was obtained by controlled hydrogenation of nitrobenzene in alkaline medium (yield 80%) [572] and by reduction with sodium bis 2-methoxyethoxy)alumium hydride (yield 37%) [544],... 

To a mixture of 50 g (0.4 mol) of nitrobenzene, 180 ml of 30% sodium hydroxide, 20 ml of water and 50 ml of ethanol, 100-125g (1.5-1.9g-atom) of zinc dust is added portionwise with efficient mechanical stirring until the red liquid turns light yellow. After stirring for an additional 15 minutes, 1 liter of cold water is added, the mixture is filtered with suction, the solids on the filter are washed with water, and the hydrazobenzene is extracted from the solids by boiling with 750 ml of ethanol. The mixture is filtered while hot, the filtrate is cooled, the precipitated crystalline hydrazobenzene is filtered with suction, and the mother liquor is used for repeated extraction of the zinc residue. Recrystallization of the crude product from an alcohol-ether mixture gives hydrazobenzene of m.p. 126-127°. 

Azoxybenzene is reducible under polarographic conditions. The final product is hydrazobenzene formed in an irreversible process for which the half-wave potential [105] varies with pH as illustrated in Fig. 11.3. The half-wave potential is close to that of the nitrobenzene. Azobenzene, which is an intermediate in the process, is... 

They can be isolated in good yields by reduction of the nitrobenzene in aqueous ethanolic sodium acetate under reflux, passing around 10% excess electric charge [103]. Any hydrazobenzene formed is rapidly oxidised back to the azobenzene by air during work-up. Azoxybenzene is formed first and then reduced to azobenzene and finally hydrazobenzene at the cathode. A solution electron transfer reaction between azoxybenzene and the hydrazobenzene reforms azobenzene. 

Aniline may be made (I) hy Ihe reduction, with iron or tin in HOI, of nitrobenzene, and (2) by the amination of chlorobenzene by healing with ammonia to a high temperature corresponding to a pressure of over 200 atmospheres in the presence of a catalyst (a mixture of cuprous chloride and oxide). Aniline is the end-point of reduction of most mono-nitrogen substituted benzene nuclei, as nitrosobenzene, beta-phenylhydroxylamine. azoxybenzene, azobenzene, hydrazobenzene. Aniline is detected by the violet coloration produced by a small amount of sodium hypochlorite. 

Compounds related to aniline, either directly or by oxidation, and to nitrobenzene by reduction, are numerous and important. When nitrobenzene is reduced in the presence of hydrochloric acid by tin or iron, the product is aniline (colorless liquid in die presence of water by zinc, the product is phenylhydroxylamine (white solid) in the presence of methyl alcohol by sodium alcoholate 01 by magnesium plus ammonium chloride solution, the product is azoxybenzene (pale yellow solid) by sodium stannitc, or by water plus sodium amalgam, the product is azobcnzcnc (red solid) in the presence of sodium hydroxide solution by zinc, the product is hydrazobenzene (pale yellow solid). The behavior of other nitrocompounds is similar to that of nitrobenzene. 

Hydrazobenzene.—100 gms. nitrobenzene, 100 gms. of cone, caustic soda (30% solution) and 100 gms. water are placed in the reduction pan (see Fig. 37) and heated to 95°, and all external heat cut off. Zinc dust of good qualify (over 85% metallic zinc) is then added, a few gms. at a time. The heat of reaction will raise the temperature to 100°, and when it cools to 98° a few more gms. of zinc dust are added, the temperature being allowed to drop to 98° before any further addition of zinc is made. 

Pentonitroozobenzene, (N02)3 -CjHj N QHj NOjJj orn colored ndls (from glacial acetic acid mp 213°, explodes on heating above its mp readily sol in acet, ethyl acetate or nitrobenzene diffc sol in ale, eth or benz. It was prepd by heating an acetonic soln of 2,4,6,2,4 -pentanitro-hydrazobenzene, [(N02)2-C8H3-NH-NH-QH2-(N02)3], with an excess of lead peroxide for Vi hr... 

Oxyphenbutazone was synthesized (8) by condensation of the protected aminophenol (I, Scheme 2) with nitrobenzene (II). Reduction of the resulting azo-compound (III) gave the hydrazobenzene (IV) which when condensed with diethylbutyl-... 

Hydrazobenzene is also to be produced in India 276) by electrochemical reduction of nitrobenzene. Azoxybenzenes can be reduced to benzidines with TiCl3 in a solution containing hydrochloric acid 590) ... 

When reduced by electrolysis, nitrobenzene and its homologues yield the same products as may be obtained by the various chemical methods of reduction. Aniline, azobenzene, azoxybenzene, hydrazobenzene, and -amino-phenol, as well as phenylhydroxylamine, can thus be obtained from nitrobenzene, and most, if not all, of these products could be prepared satisfactorily on an industrial scale by electrolysis, by adjusting the manner of working so that economy of energy is combined with maximum yields. Many of these products demand a comparatively high price, so that low power cost is not so important in this class of manufacture as high percentage yields. 

This work was extended by Elbs and his pupils,1 and the processes were protected by patents.2 Subsequently alcohol was dispensed with and aqueous caustic soda employed. For example, an emulsion of nitrobenzene in 10 per cent, aqueous sodium hydroxide may be reduced with a cathode of lead or nickel in a porous earthenware cell, with a current density of 10-12 amps, per dm.2 An anode of graphite or lead may be employed in an outer containing vessel filled with sodium hydroxide solution or sodium sulphate. Azo- or hydrazobenzene is obtained according to the quantity of electricity passed through, and the azobenzene emulsion can be transformed into benzidine by acidifying the cathode liquor and completing the reduction.4... 

Haussermann 2 reduced nitrobenzene and nitrotoluenes both in alkaline and acid solution, the former with iron, the latter with platinum, electrodes. By reduction in alkaline solution, he obtained as principal product hydrazobenzene and hydrazo-toluene respectively in sulphuric-acid solution he got from nitrobenzene, as chief products, benzidine sulphate and azoxy-benzene, besides an easily changeable body which was not further determined. o-Nitrotoluene3 under like conditions gave o-tolui-dine sulphate besides small quantities of o-toluidine p-nitro-toluene yielded principally p-toluidine. 

We will have to suppose that the lead sponge occurring at the lead cathode reduces the nitrobenzene to aniline. Men-tionable quantities of lead sulphate cannot be found, since this is continually reconverted to lead sponge by the freed hydrogen ions. This process is analogous to the one previously published by me3 in which a hydro-alcoholic solution of nitrobenzene acidified with sulphuric acid gives aniline when a zinc cathode is used. Considerable quantities of zinc sulphate do not occur. At a platinum cathode, under the same conditions, no aniline is formed, but azoxybenzene and hydrazobenzene or benzidine form. This has been confirmed by Haussermann. 4... 

Benzidine.—That nitrobenzene, by electrolytical reduction in acid solution, can directly yield benzidine, was first proved by Hiiussermann,1 who used sulphuric acid. Lob 2 later proved the same to be true for hydrochloric-, acetic- and formic-acid electrolytes. However, several reactions predominate in this direct acid reduction, which prevent the carrying out of the reaction up to hydrazobenzene, or the formation of benzidine. Phenylhydroxylamine may particularly be mentioned in this connection. In alcoholic-acid solution it is partly rearranged to amidophenol or its ethers, and partly reduced to aniline. Azoxybenzene, in acid solution, is the starting-point in the benzidine formation however, in this case, the combining velocity of nitrosobenzene and phenylhydroxylamine is not very great, so that the latter is to a very considerable extent subject to the more rapidly acting influence of the acid. 

Similar to the cases with platinum metals, the rate of hydrogenolysis of hydrazobenzene appears to be smaller than that of azobenzene over Raney Ni as well,234 although Wisniak and Klein observed the formation of only azoxy- and azobenzenes, and no hydrazobenzene, during the course of hydrogenation of nitrobenzene over Raney Ni at 170°C and 1.38 MPa H2.235... 

Electrolytic reduction, as in the preparation of hydrazobenzene from nitrobenzene, or of p-aminophenol from nitrobenzene. The latter reduction involves a simultaneous rearrangement of the intermediate phenylhydroxylamine. 

Finally, iron can also exert a reducing action when used in the presence of caustic alkali and nitrobenzene is converted successively to azoxy-, azo-, and hydrazobenzene under these conditions. Especially finely ground cast iron powder must be used for this purpose, ind it must be etched before its use in some cases. 

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