Nitrobenzene, aniline from

Catalytic hydtogenation is the most efficient method for the large scale manufacture of many aromatic and ahphatic amines. Some of the commercially important amines produced by catalytic hydrogenation include aniline (from nitrobenzene), 1,6-hexanediamine (from adiponitrile), isophoronediamine (from 3-nitro-l,5,5-trimethylcyclohexanecarbonitrile), phenylenediamine (from dinitrobenzene), toluenediamine (from dinitrotoluene), toluidine (from nitrotoluene), and xyhdine (from nitroxylene). As these examples suggest, aromatic amines ate usually made by hydrogenating the... 

In the manufacture of aniline from nitrobenzene the reactor products are condensed and separated into an aqueous and organic phases in a decanter. The organic phase is fed to a striping column to recover the aniline. Aniline and water form an azeotrope, composition 0.96 mol fraction aniline. For the feed composition given below, make a mass balance round the column and determine the stream compositions and flow-rates. Take as the basis for the balance 100 kg/h feed and a 99.9 percentage recovery of the aniline in the overhead product. Assume that the nitrobenzene leaves with the water stream from the base of the column. 

The process used in the manufacture of aniline from nitrobenzene is described in Appendix G, design problem G.8. The process involves six significant stages Vaporisation of the nitrobenzene... 

Catalytic hydrogenation processes in which copper is the catalytic agent have also been recently introduced into industrial practice for the preparation of aniline from nitrobenzene. 

The production of aniline from nitrobenzene proceeds in such a way that the reactive hydrogen is added to the nitro-group, the oxygen is eliminated as water, and finally hydrogen is again added on. The process is not a simple one and involves a series of intermediate stages ... 

On the other hand, the production of desired compounds through reduction of starting material requires the electron donors to be oxidized (reductant). Alcohols are often used not only as a solvent but as the donor to produce useful compounds, e.g., anilines from nitrobenzenes,22) alcohols from aldehydes,23) and secondary amines from the corresponding Schiff bases.24) From the organic synthetic point of view, however, the separation of undesired products, aldehydes or ketones, from the alcohols is necessary unless subsequent reaction processes consume them25,26) or they are easily removed by distillation or other procedures. A recent report has shown that water acts as the electron donor and is converted into 02 in the photocatalytic regio-selective reduction of terpenes mixed with aqueous suspension of Ti02.27,28) It is notable that isolation of the desired product from the reaction mixture is simple in this type of photocatalytic reduction. 

Other products of an alkali amalgam decomposition process are sodium sulfide from polysulfide solutions, sodium dithionide from hydrogen sulfide, hydra-zobenzene or aniline from nitrobenzene, and adiponitrile from acrylonitrile. Last but not least alkali metals can be prepared directly from the amalgam [33]. 

The dinitrotoluenes are reduced quantitatively in a succession of high pressure hydrogenations. The selectivity to the toluenediamines is 98-99%. In contrast to the manufacture of aniline from nitrobenzene, gas-phase hydrogenation is not used commercially due to the readily explosive decomposition of the dinitrotoluenes at the required reaction temperatures. Purification is done in a series of distillation columns. 

Hydrocarbon nitro derivatives can also be reduced by this reagent Allen70 obtained up to 100% of aniline from nitrobenzene. Bimolecular intermediates are rarely obtained in spite of the alkalinity of the reaction medium. The proportions of reactants used are in accord with the reaction ... 

A paper presented at the previous symposium [8J shows that formation of aniline from nitrobenzene is also possible over oxidic solid catalysts. Kijehski found that MgO is a good catalyst for formation of aniline, when hydrogen atoms are supplied from a hydrogen donor (like isopropanol). Formation of... 

Vapor-phase reductions are sometimes fraught with a number of technological problems (1) limited per-pass conversion, thus necessitating separation of aniline from nitrobenzene (unless the heat of reaction is gainfully employed, this will constitute a significant item of expense), and (2) sensitivity of catalytic operations which may result in overreduction and Pharm. Soc. Japatif 74, 889 (1954). 

Working under favorable conditions with a nickel catalyst. Brown and Henke obtained a 95 per cent yield of aniline from nitrobenzene. With a constant rate of flow of nitrobenzene, the yields drop off with too much or too little hydrogen. This fluctuation has been ascribed to over- or underreduction. Since nickel is such an active catalyst for this purpose, reduction of the aniline to cyclohexane and ammonia is known to take place. 

Solvents can be effectively used to increase the selectivity of an intermediate in a consecutive reaction by forcing the desorption of the desired compound from the catalyst surface and thus preventing further reaction. A good example of this is the formation of benzene hydroxylamine (45), an often undetected intermediate in the production of aniline from nitrobenzene (reaction 6.40). 

Although some mechanistic studies have been published about this reaction, a general route for the formation of an aromatic amine or aromatic aminosulfonic acid has been proposed. However, mechanistic details are not available from the literature. Displayed here is a tentative mechanism for the production of aniline from nitrobenzene. The formation of 2- and 4-aminobenzenesulfonic acid should proceed along a similar pathway. 

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