OF ARTS AND SCIENCES. 289 



Preparation of Tetrabromdinitrobenzol. 



Our starting point in the manufacture of the tetrabrombenzol was 

 tribromaniline, which we prepared as follows. 60 grs. of aniline were 

 dissolved in dilute hydrochloric acid, and the solution, having been 

 made up to a volume of about three litres, a rapid stream of air satu- 

 rated with bromine vapor was sucked through it by means of a Bunsen 

 pump, until the liquid assumed a distinct yellow color. The precipi- 

 tate of tribromaniline was then removed by straining through cheese- 

 cloth, 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 tribromaniline free from colored by- 

 products was obtained at a much less expense of time and labor than 

 by the method formerly in use. 



To convert the tribromaniline into tetrabrombenzol we used the 

 method of V. von Richter* slightly modified, which left nothing to be 

 desired so far as the yield was concerned, when the process was suc- 

 cessful ; this, however, was not always the case, as frequently the 

 product was a substance melting in the neighborhood of 87°, from 

 which tetrabrombenzol melting at 98° could be obtained only by re- 

 peated crystallization from a mixture of alcohol and benzol, and even 

 then not in large quantity.f In spite of many experiments, we have 

 not succeeded in determining with certainty the conditions under 

 which this mixture was formed, or the nature of the impurity which 

 it contained, and can give only the conditions which usually gave a 

 good result. 25 grs. of the tribromaniline were dissolved in a small 

 quantity of glacial acetic acid with the aid of heat, and, after the solu- 

 tion had cooled, a concentrated aqueous solution of hydrobromic acid t 

 was added, which threw down a precipitate of tribromaniline bromide ; 

 the mixture was stirred vigorously, and, disregarding the precipitate, a 

 concentrated aqueous solution of about the theoretical amount of sodic 

 nitrite added in small portions, keeping the solution cool by immersing 

 the beaker containing it in cold water ; the beaker was then warmed 

 gently on the water bath, and solid sodic nitrite added in small pieces 



* Cer. d. ch. G , viii. 1428. 



t Owing to this uncertainty in our modification of Von Richter's process, we 

 made two attempts to use Sandmeyer's method, but encountered such difficul- 

 ties in applying it to tribromaniline that we decided it was easier to prepare our 

 material by Von Richter's process than to overcome these difficulties. 



J An attempt to substitute potassic bromide and sulphuric acid for hydro- 

 bromic acid gave a much poorer yield ; less than 50 per cent instead of 90. 



vol. xxiv. (n. s. xvi.) 19 



