Nitrobenzene bromonitrobenzene

Pour the resulting dark reddish-brown liquid into 500 ml. of water to which 17 ml. of saturated sodium bisulphite solution has been added (the latter to remove the excess of bromine). Steam distil the resulting mixture (Fig. II, 41,1) , collect the first portion of the distillate, which contains a little unchanged nitrobenzene, separately. Collect about 4 litres of distillate. Filter the yellow crystalline solid at the pump, and press well to remove the adhering liquid. The resulting crude m-bromonitrobenzene, m.p. 51-52°, weighs 110 g. If required pure, distil under reduced pressure (Fig. II, 19, 1) and collect the fraction of b.p. 117-118°/9 mm. it then melts at 56° and the recovery is about 85 per cent. 

Intermediates benzene to nitrobenzene to m bromonitrobenzene to m bromoanihne to m bromophenol Reagents HNO3 H2SO4 Br2 FeBr3 Fe HCl then HO NaN02 H2SO4 H2O then heat in H2O... 

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. 

Intermediates benzene to nitrobenzene to i-bromonitrobenzene to i-bromoaniline to m-bromophenol. Reagents HNO3, H2SO4 Br2, FeBr3 Fe, HCl then HO NaN02, H2SO4, H2O, then heat in H2O. 

The reaction product, which is a dark reddish-brown liquid, is poured or siphoned (Note 5) into 1.5 1. of water to which 50 cc. of a saturated solution of sodium bisulfite has been added (Note 6). The mixture is distilled with steam (Org. Syn. 2, 80) and the first portion of the distillate is collected separately to remove a small amount of unchanged nitrobenzene. It is necessary to collect about 12 1. of distillate in order to obtain all of the m-bromonitrobenzene. The yellow crystalline solid is filtered with suction and pressed well on the funnel to remove water and traces of nitrobenzene. The yield of crude product varies from 270-340 g. (60-75 Per cent °f the theoretical amount). It melts at 51.5-520 and boils at 117-118 79 mm. This product is satisfactory for most purposes. If a purer material is desired, the crude /w-bromonitrobenzene may be distilled under reduced pressure. The recovery on purification is about 85 per cent. Briihl recorded the b.p. as 1380/18 mm. and the m.p. as 56° for pure wz-bromonitrobenzene.1... 

One can prepare bromonitrobenzenes either by nitrating bromobenzenc or by brominating nitrobenzene. Will these two reactions give the same product (or product distribution) If not, how will the products differ ... 

The compound l-bromo-4-nitrobenzene (p-bromonitrobenzene) can be brominated. What do you expect to be the major product and why Draw appropriate Lewis structures to support your answer. 

Bromination of nitrobenzene. Bromination of nitrobenzene can be effected by addition of KBrO., (slight excess) to the arene in aqueous H2S04 (1 1 v/v) at a rate such that the temperature docs not exceed 35". The 3-bromonitrobenzene thus obtained (76 91% yield) is contaminated with a slight amount of dibromonitroben-... 

Fig. 29.10 H-NMR spectra of (a) methylbenzene (b) methoxybenzene (c) nitrobenzene (d) 1,4-dimethylbenzene (e) 4-methoxynitrobenzene (f) 4-amino-3-bromonitrobenzene (NH2 protons not shown).

Other reactions go the same way so that bromination of nitrobenzene gives meta-bromonitrobenzene in good yield. The combination of bromine and iron powder provides the necessary Lewis acid (FeBr3) while the high temperature needed for this unfavourable reaction is easily achieved as the boiling point of nitrobenzene is over 200 "C. 

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