JACKSON AND CALVERT. — DERIVATIVES OF BENZOL. 125 



hand, was entirely unaffected by a solution of sodic etiiylate in open 

 vessels. These experiments show that the presence of the three bro- 

 mine atoms exercises a loosening effect similar to that exhibited by 

 nitro oToups, although much weaker in degree. They also furnish 

 an additional case in which the stability of the aromatic compounds 

 of the different halogens increases in the order iodine, bromine, chlo- 

 rine. This is worth noting, because Korner * states that the halo- 

 gens are removed from dinitrohalogenbeiizols (X 1, NOg 2, NO2 4) 

 in exactly the reverse order ; that is, chlorine most and iodine least 

 easily. 



We next turned our attention to the tetrabrombenzol melting at 

 174°_175° which has been proved by work done in this Laboratory to 

 have the symmetrical constitution Br.Br.H.Br.Br.H, as in this sub- 

 stance only two of the bromine atoms are in the positions to the one 

 to be removed (ortho and para) which had proved effective in the 

 unsymmetrical compound. This, however, did not affect the result 

 materially, as this tetrabrombenzol was converted into unsymmetrical 

 tribrombenzol (Br 1, Br 2, Br 4) by the boiling solution of sodic 

 ethylate to about the same extent as the unsymmetrical tetrabromben- 

 zol. In separating the small quantity of tribrombenzol formed from 

 the large amount of unaltered tetrabrombenzol we have obtained 

 excellent results in both the cases just mentioned by exposing the mix- 

 ture for a long time to the lowest temperature at wiiich anything 

 sublimes. The sublimate tlius obtained, if not the pure tribrombenzol, 

 could be converted into it by a single repetition of this rough fractional 

 sublimation. 



An arrangement of the bromine atoms entirely different from the 

 effective ortho para positions is found in the symmetrical tribrom- 

 benzol Br.H.Br.H.Br.H, as here all the halogen atoms are in the meta 

 position to each other, but, as has been already mentioned, Blau found 

 that one of the atoms of bromine was removed by the action of sodic 

 methylate at 130°. As our work just described has shown that sodic 

 ethylate is more active than the methylate, we thought this might act 

 even in open vessels, and on trying the experiment have found that 

 sodic ethylate in boiling alcoholic solution removes from symmetrical 

 tribrombenzol a portion of its bromine. The organic products of the 

 partial reaction were oily, but, as the object of our experiment was to 

 determine whether a reaction took place, and not what its products 

 were, no attempt was made to examine them. This is not the only 



* Gazz. Chim., 1874, p. 323, note. 



