W-Bromonitrobenzene

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... 

Intermediates benzene to nitrobenzene to w-bromonitrobenzene to w-bromoaniline to m-bromophenol. Reagents HN03, H2S04 Br2, FeBr3 Fe, HCl then HO- NaN02, H2S04, H20, then heat in H20. 

Pour the resulting dark reddish-brown liquid into 500 ml of water to which 17 ml of saturated sodium metabisulphite solution has been added (the latter to remove the excess of bromine). Steam distil the resulting mixture (Fig. 2.102) 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 w-bromonitrobenzene, m.p. 51-52 °C, weighs 110 g (74%). If required pure, distil under reduced pressure (Section 2.27) and collect the fraction of b.p. 117-118 °C/9mmHg it then melts at 56 °C and the recovery is about 85 per cent. 

A yield of 84 per cent of 0-nitrodiphenyl ether boiling at 183-185 °/8 mm. is obtained when o-nitrochloro benzene is used. For the preparation of m-nitro diphenyl ether, the method of Ullmann and Sponagel,1 using w-bromonitrobenzene, seems to be the best, since w-chloro nitrobenzene gives large amounts of tarry matter. 

However, we know that a nitro group is a meta director. So, we first make nitrobenzene, then bromi-nate it to obtain w-bromonitrobenzene. 

First of all, we must consider the order in which we introduce these various substituents into the ring. In the preparation of the bromonitrobenzenes, for example, it is obvious that if we nitrate first and then brominate, we will obtain the w-isomer whereas if we brominate first and then nitrate, we will obtain a mixture of the o- and p-isomers. The order in which we decide to carry out the two steps, then, depends upon which isomer we want. 

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