OF ARTS AND SCIENCES. 273 



Preparation of Tribromdinitrobenzol. 



The method used by us for preparing tribromdiuitrobenzol differs 

 from that formerly, in use only in certaiu details, but, as careful atten- 

 tion to these details insures a purer product at much less expense of 

 time and labor, we have thought it best to give a full account of our 

 mode of procedure. 



To make the tribromaniliue, GO grs. of aniline were dissolved in 

 dilute hydrochloric acid, and, the solution having been made up to a 

 volume of about 3 litres, a rapid stream of air saturated with bromine 

 vapor was sucked through it by means of a Bunsen pump, until the 

 liquid assumed a distinct yellow color. The precipitate of tribrom- 

 aniliue was then removed by straining through cheese-cloth, and 

 washed with a stream of common water, until free from acid, when 

 the greater part of the water was squeezed out with a screw press, and 

 the product thoroughly dried on a steam radiator. In this way a 

 quantitative yield of the tribromaniliue was obtained, and it was free 

 from colored by-products. 



In order to convert the tribromaniline into tribrombenzol, 50 grs. of 

 it, after being pulverized, were dissolved with the aid of heat in about 

 300 c.c. of common alcohol, and a concentrated aqueous solution of 

 21 grs. of sodic nitrite poured in slowly, but not in successive portions. 

 The hot mixture was then acidified with dilute sulphuric acid, and 

 allowed to stand over night, when it was filtered, and the precipitate 

 washed with hot water to remove the sodic sulphate and leave the 

 tribrombenzol. An additional quantity of this was obtained by con- 

 centrating the alcoholic filtrate, when it separated as an oil, that solidi- 

 fied on standing, and was then crystallized from alcohol. The yield 

 was nearly quantitative, as 45.50 grs. of tribrombenzol were obtained 

 instead of the 47.77 required by the theory, that is 95 per cent. 

 When made by this method, the tribrombenzol was usually pure 

 enough to be nitrired directly in spite of its brownish color.* 



* The amount of sodic nitrite used in the process described above (two mole- 

 cules of nitrite to one of the base) is twice that required by the theory, but we 

 have found that this larg-e excess was necessary to bring all the tribromaniline 

 into the reaction. When a smaller amount of nitrite was used, the product was 

 much less pure, as shown by its lower melting point ; it was necessary in this 

 case to distil it from a little retort, and crystallize several times from alcohol, to 

 obtain pure tribrombenzol. The crystals obtained on evaporating the alcoholic 

 mother liquors, which made up about two thirds of the entire amount, were dis- 

 tilled with steam, pushing the distillation as rapidly as possible, when tribrom- 

 benzol passed over, and tribromaniline was left in the retort ; but all this tedious 

 purification can be avoided by using the excess of nitrite recommended above, 

 vor.. xxiv. (y. s. xvi.) 18 



