Reaction CLXVI.—Replacement of the Amino Group by Halogen

Reaction CLXVI. Replacement of the Amino Group by Halogen.— 

ortfto-toluidine are dissolved in a mixture of 35 c.cs. hydro-bromic acid of constant boiling pont, and 40 c.cs. of water. The solution is cooled to 0°, and diazotised by the addition of 5 gms. sodium nitrite dissolved in 12 c.cs. of water during this addition a drop is frequently removed, diluted with water on a watch-glass, and tested with starch-iodide paper for free nitrous acid (see p. 373). Copper powder (prepared from 40 gms. copper sulphate, see p. 508) is then added in small quantities at a time to the diazonium solution, which should be continuously stirred an effervescence—due to the escape of nitrogen—takes place. When addition of copper produces no further effervescence, the bromo-toluene forms the lower layer. This layer is separated, steam distilled and the distillate extracted with ether. The ethereal solution is dried over solid calcium chloride, and fractionated. 

20 gms. (1 mol.) of p-toluidine are dissolved in 100 c.cs. of a mixture of equal volumes of water and cone, hydrochloric acid, and diazotised in the usual way (see p. 372) with sodium nitrite. 15 gms. of moist copper powder (see p. 508) are then added in small portions to the well-stirred solution. When the evolution of nitrogen has ceased, the product is steam distilled, the distillate extracted with ether, and the ethereal solution dried over anhydrous sodium sulphate. The sodium sulphate is filtered off and the filtrate distilled. p-Chorotoluene passes over at 163°. 

20 gms. aniline are dissolved in 130 c.cs. water and 37 c.cs. cone, hydrochloric acid and diazotised (see Preparation 379) at 0°—5° by the addition of 15 gms. sodium nitrite dissolved in 40 c.cs. water. 140 c.cs. of a 10% solution of cuprous chloride (p. 507) are heated nearly to boiling in a flask and the diazonium solution run in gradually, the contents of the flask being occasionally shaken, and maintained near boiling during the addition. 

The yellow precipitate which appears on the introduction of the diazonium solution decomposes almost immediately, yielding chlorobenzene and nitrogen. The contents of the flask are submitted to steam distillation until no more oily drops of chlorobenzene pass over. The distillate is extracted with ether, the ethereal solution dried over calcium chloride and fractionated. 

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