Preparation of nitrobenzene

Nitrobenzene is prepared by the nitration of benzene with mixtures of nitric and sulphuric acids of the composition ranging from  

The quantity of nitrating mixture is calculated with a small excess of HN03 (1%), or the nitration is carried out with a volume of mixture insufficient for complete nitration (e.g. 95-97.5%). In the latter case the spent acid does not contain any nitric acid or nitrogen oxides. Nitrobenzene, together with unreacted benzene, is separated from the spent acid. Then benzene is separated from nitrobenzene by distillation. The yield generally amounts to 98% on a large scale, and to about 95% in the laboratoiy. 

At present the nitration of benzene is one of the simplest processes in the organic chemical industry. Nevertheless, the safety factor should not be neglected. The explosion in Rummelsburg of the plant for the nitration of benzene to nitrobenzene, described earlier (p. 152), was the result of defective operation of the nitrator. 

The manufacture of nitrobenzene on an industrial scale in the Griesheim (I. G. Farbenindustrie) plant is described below  

At the beginning of acidification a temperature of 25°C should be maintained. During the addition of the first 4000 kg of acid the temperature is allowed to rise up to 35°C. On adding a further 2500 kg of acid the temperature rises up to 60°C. Then the whole is mixed for an hour at 70°C. After cooling, the layer of nitro compound is separated from that of the acid. The spent acid is shaken with benzene to remove any nitrobenzene, nitric acid and nitrogen oxides that may be left. Then the spent acid is transferred to a distillation plant, where it is subjected to concentration up to 70% of H2S04. The benzene from the extraction is either recycled to the nitration plant or is distilled off to separate it from nitrobenzene. 

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Preparation of Nitrobenzene. One hundred and fifty grams of concentrated sulfuric acid (d. 1.84) and 100 grams of nitric acid (d. 1.42) are mixed in a 500-cc. flask and cooled to room temperature, and 51 grams of benzene is added in small portions at a time with frequent shaking. Shaking at this point is especially necessary lest the reaction suddenly become violent. If the temperature of the mixture rises above 50-60°, the addition of the benzene is interrupted and the mixture is cooled at the tap. After all the benzene has been added, an air condenser is attached to the flask and the material is heated in the water bath for an hour at 60° (thermometer in the water). After cooling, the nitrobenzene (upper layer) is separated from the spent acid, washed once with water (the nitrobenzene is now the lower layer), then several times with dilute sodium carbonate solution until it is free from acid, then once more with water, dried with calcium chloride, and distilled (not quite to dryness). The portion boiling at 206-208° is taken as nitrobenzene. 

Nitration of aromatic hydrocarbons is usually carried out with the above mixed acid reagent at comparatively low temperatures (e.g. about 50 °C, as used in the preparation of nitrobenzene and 1-nitronaphthalene, Expt 6.17). Unnecessarily high temperatures should be avoided since polynitration is then more likely and oxidative breakdown of the aromatic ring system may occur. 

Consider the preparation of nitrobenzene, C H5N02, by the reaction of a limited amount of benzene, CgHg, with excess nitric acid, HNO3. The balanced equation for the reaction may be written as... 

Nitrobenzene Physical properties Chemical properties Toxicity of nitrobenzene Preparation of nitrobenzene Diniirobenzcnes Physical properties Chemical properties Toxicity of dinitrohenzenes Explosive properties of diniirobenzene Sensitivity to impact Preparation of dinitrohenzenes Nitration in two stages in two niirators Purification... 

Liquid Nitro Aromatic Compounds 4.6.1 Properties and Preparation of Nitrobenzene... 

It is prepared by reduction of nitrobenzene with iron and NaOH. It is also prepared by an electrolytic reduction of nitrobenzene. It is widely used for the preparation of benzidine. 

CijHgNj. Made by heating o-pheny-lenediamine with glycerol, nitrobenzene and cone, sulphuric acid. It exists as a monohydrate, m.p. 94" C, or anhydrous, m.p. 117°C. It is used as a complexing reagent in the estimation of Fe and in the preparation of numer-... 

Nitrobenzene is a pale yellow liquid, having a b.p. 210 , and dy 1 20. It has an odour which is similar to that of almonds, and which is therefore often confused with that of benzaldehyde. Nitrobenzene is used chiefly for the preparation of aniline. 

Azoxybenzene is readily prepared by reduction of nitrobenzene in an alkaline medium with dextrose or sodium arsenite ... 

Nitration of benzene yields nitrobenzene, which is reduced to aniline, an important intermediate for dyes and pharmaceuticals. Benzene is chlorinated to produce chlorobenzene, which finds use in the preparation of pesticides, solvents, and dyes. 

Phenazine mono-N-oxides have also been prepared from nitrobenzene derivatives. Condensation of nitrobenzene with aniline using dry NaOH at 120-130 °C results in modest yields of phenazine 5-oxide, although the precise mechanism of this reaction is not well understood (57HC(ll)l) with unsymmetrical substrates it is not possible to predict which of the isomeric fV-oxides will be produced. Nitrosobenzene derivatives also function as a source of phenazine mono-fV-oxides thus, if 4-chloronitrosobenzene is treated with sulfuric acid in acetic acid at 20 °C the fV-oxide is formed (Scheme 21). 

A yield of 84 per cent of u-nitrodiphenyl ether boiling at i83-i85°/8 mm. is obtained when o-nitrochloro benzene is used. For the preparation of j-nitro diphenyl ether, the method of Ullmann and Sponagel, using m-bromonitrobenzene, seems to be the best, since m-chloro nitrobenzene gives large amounts of tarry matter. 

The preparation of 5,6-diaminobenzofuroxan, by decomposition of l,2-diamino-4-azido-5-nitrobenzene, has been reported. ... 

For the preparation of nitrocymene a method developed in the Colour Laboratory and described in the Jour, of Ind. and Eng. Chem. in 1918, p. 453, was used. The nitro group enters in the ortho position with respect to the methyl group. The reduction of this compound to aminocymene or cymidine was accomplished by means of iron powder and hydrochloric acid in exactly the same way as nitrobenzene is reduced to aniline. 

Preparation of 4-Phenyl-4-Cyano-N-Methyl Azacydoheptane Methobromide A 0.1 M nitrobenzene solution of 1-dimethylamino-3-cyano-3-phenyl-6-bromohexane was kept at 100°C for 1 hour whereby the quaternary salt precipitated out MP 246 to 247 C. 

Prepare a stock solution of nitrobenzene by dissolving about 0.25 g (accurately weighed in a weighing bottle) in 50 mL of 95 per cent ethanol, and adding this to 450 mL of the buffer solution contained in a 500 mL graduated flask. Rinse the weighing bottle with two successive 5mL portions of 95 per cent ethanol and add each rinsing to the 500 mL flask finally make the flask up to the mark with buffer solution. 

Diethyl methylphosphonite in refluxing dialkylamine is the favored method for the formation of 37/-azepines from nitroarenes,75,176,207 although tributylphosphane and tri-piperidinophosphane are recommended for the deoxygenation of nitrobenzene in piperidine.79 Deoxygenation of nitrobenzene in diethylamine furnishes Ar,Ar-diethyl-3/f-azepin-2-amine, and a range of 5-substituted 3//-azepines 97 have been prepared in a similar manner from 4-sub-stituted nitroarenes.79,176 Curiously, the corresponding 2-substituted nitroarenes, with the exception of 2-nitrotoluene, yield only tarry products. 

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