( G79 ) 



The necessary experiments lia\e been considerably delayed, because 

 it appeared that tlie ortho- and meta-dibromobenzenes iiad not as 

 yet been obtained in a perfectly pure condition, and the search for 

 a good method absorbed much time. We have at last succeeded in 

 preparing /;i-dibromobenzene from perfectly pure »i-bromoaniIine by 

 diazotation in a dilute hydrobromic acid solution, according to a 

 direction given by Ekdmann for another purpose. J/^^/frt-dibromobenzene 

 has a sp. gr. of 1.960 at 3 8.5°, and solidifies at — 7°. It is true 

 that F. ScHiFF incidentally mentions (M. 11, 335) 'that he has met 

 with /)«-dibromobenzene solidifying at -|- 1°, without saying how he 

 has obtained the same, but there is good reason for doubting the 

 correctness of this statement. In this case, the product obtained by 

 me and my coadjutors (Sirks, Sluiter) with its 8° lower solidifying 

 point should contain about 167„ of impurities. In the nitration of 

 our Hz-dibromobenzene, however, a product is obtained having a 

 sp. gr. such as was to be expected from a mixture of the isomers 

 (Br' : Br' : NO/) and (Br' : Br' : NO./) brought together in the propor- 

 tion indicated by the solidifying point, so that a contamination of 

 our preparation with such a large quantity of another substance is 

 altogether out of the question ; moreover, on distillation our preparation 

 yielded two fractions within one degree which both possessed 

 practically the same sp. gr. and solidifying point. 



d^-dibromobcuzene which was obtained in an analogous manner 

 from o-bromoaniline, had a sp. gr. of 1.996 at Ji° and solidified 

 at + 6°. 



The preparation of the six dibronionitrobenzenes was carried out 

 in a manner analogous to tiiat of the six dichloronitrobenzenes, 

 described by me in the "Recueil" 23, 357. 



The composition of the products of nitration of the dibromobenzenes 

 was determined from their solidifying point and their sp. gr. and 

 led to the results united in the subjoined table with the composition 

 of the products of nitration of the dichlorobenzenes. The temperature 

 of the nitration was 0°. (See p. 680). 



In ortho-dibromobenzene the disturbance of the directing power of 

 the one halogen atom owing to the presence of the other one is, 

 therefore, much less than in tiie case of orthodichlorobenzene because 

 in the first one 18.3 and in the second only 7.27o of b^^-product 

 is formed, whilst monobromo- and monochlorobenzene yield, respec- 

 tively, 29.8 and 37.6"/(i of by-product. On the other hand, the 

 disturbance caused by the entr^ of the nitro-group between the two 

 halogen atoms in ///-dibromobenzene is very nearly o((ual to that in 

 Hi-dichlorobeiizene, therefore much larger in regard to tiie ortho- 



