Reaction:

For the preparation of aniline from nitrobenzene we use an autogenously welded iron reaction vessel, such as is shown in Fig. 4 (p. 11),1 This apparatus is provided with a condenser and dropping funnel, and is charged with 200 gms. iron turnings, 300 c.cs. water, and 20 c.cs. of 30 % hydrochloric acid. The mixture is boiled up for 10 minutes in order to etch the iron. 123 Gms. nitrobenzene are then dropped in during three-quarters hour at the boil, with very vigorous stirring, taking care that the iron is kept continuously swirled up. Considerable heat is evolved, and the nitrobenzene is reduced to aniline, whilst the iron becomes oxidized to Fe3O4. Boiling is continued under the reflux until the distillate which runs back down the condenser is colourless. 15 Gms. soda are then added to the reduction liquid and the aniline driven over with steam. The steam is led in through the neck which held the thermometer,

200 gms. Fe.

300 c.cs.

H2O.

20 c.cs. HCl.

1 mol. Nitrobenzene = 123 gms.

15 gms. Na2Co3 or CaO.

1 A similar apparatus may be used with advantage for sulphonating by means of oleum, as it is unbreakable, and, therefore, quite free from any possible dangers which might attend the use of glass or porcelain pots.

the condenser is fitted to the main opening by means of a bent glass tube, and the third opening is closed up.

Aniline is soluble in water, 100 gms. of water dissolving about 3 gms. of aniline. For this reason enough salt must be added to the aqueous suspension to make a 20 % solution of salt, in which aniline is completely insoluble. After standing for several hours the aniline is run off through a separating funnel and distilled over a naked flame. The first portions contain traces of benzene and a little water, the main fraction coming over at 1820 (99 %).

The yield is about 85 gms. aniline from 123 gms. nitrobenzene.

Notes on Works Technique and Practice. - In the works the aniline is distilled over by means of steam which is already saturated with aniline, i.e. the boiler is fed with the waste water from the steam distillation. Weiler-ter-Meer, however, simply extract the aniline water with nitrobenzene, the base being completely removed from the liquid by this means. The mixture of nitrobenzene and aniline is then reduced directly as described above. By this means it is possible to avoid the use of boilers charged with aniline water which always cause a certain amount of inconvenience. Fig. 12 (Plate V.) and Fig. 11 (Plate IV.) show the type of apparatus used in the factory.

On the large scale the iron is added gradually and less water is used. The yields obtained are practically quantitative, about no kgs. pure aniline being obtained from 100 kgs. benzene. This is distilled in vacuo in quantities of 10,000-30,000 kgs. The heating is always effected by a system of steam pipes fitted inside the still.

The introduction of the manufacture of aniline gave the first impetus to the development of the colour industry, as aniline has always been one of its most important products. It was first made in England, and at the present time about 50-60 % of the output is utilized for the production of Aniline Black. It may be noted at this point that only a small proportion of the so-called "Aniline Dyes "are actually derivatives of aniline.