128 PROCEEDINGS OF THE AMERICAN ACADEMY. 



diamine, observed by Ziucke aud Sinteuis, is not in harmony with 

 this inference of Schlieper. Although, therefore, the diortho position 

 is not essential to the removal of bromine by tin and hydrochloric acid, 

 there is no doubt that Schlieper is right in considering it the most 

 favorable position for this purpose, as the replacement by hydrogen 

 of an atom of bromine standing between two nitro groups has been 

 repeatedly observed in this laboratory with comparatively weak re- 

 ducing agents, such as sodium malonic ester, and probably sodium 

 acetacetic ester, or sodic ethylate. 



In trying to find the cause of the replacement of all three atoms of 

 bromine by hydrogen in the reduction of tribromdiuitrobenzol the most 

 obvious theory was that the attachment of the atoms of bromine to the 

 benzol ring was weakened by the presence of the two negative nitro 

 groups, as is so frequently observed in other reactions. If this was the 

 case, the bromine would be removed before the nitro groups were 

 reduced, and tribromphenylene diamine would not lose its bromine on 

 treatment with tin and hydrochloric acid. Upon ti-ying this experiment, 

 however, we found that the whole of the bromine was removed from 

 the tribromdiamine as easily as from tribromdiuitrobenzol.* It follows, 

 therefore, that the nitro groups are not the cause of the easy removal 

 of the three atoms of bromine in the reduction of tribromdiuitrobenzol. 

 A parallel experiment with dibroraphenylene diamine showed that 

 this substance gave up its bromine with much more difficulty than the 

 corresponding tribrom compound, for whereas the tribrom derivative 

 was converted into phenylene diamine in a few minutes, it took over 

 twelve hours to bring about the same change in the dibrom compound. 

 It is evident from these unexpected results that the removal of the 

 bromine atoms depends in part upon their position toward each other, 

 and this is not strange, as in other cases it has been observed that 

 three bromine atoms, when in the symmetrical position on a benzol 

 ring, are more loosely attached than two in the meta position ; but 

 this is not the only cause of their removal, since symmetrical tribrom- 

 benzol is not reduced by tin and hydrochloric acid. It would seem, 

 therefore, that the replacement of these atoms of bromine is caused 

 principally by the fact that there are other radicals attached to the 

 ring, with little regard to the nature of these radicals, as the highly 

 positive amido groups apparently produce the same effect as the highly 

 negative nitro radicals. An additional argument for this conclusion 



* Other reagents, for instance sodic ethylate or sodic hydrate, do not remove 

 bromine from the diamine. 



