f) 3 



b46 



Chemistry. - "The riüraiion of t/te tuired dilialogen henzenes^\ 

 By Prof. A. F. Holleman. 



(Communicated in the meeting of Oct. 31, 1914). 



When in benzene are present two snbstituents and a third 

 is introduced, the snbstitution velocity caused by tiie two groups 

 already present is unequal. From the data given in the literature 

 it may be deduced that those velocities for the snbstituents pointing 

 to the p-o-positions decrease in the subjoined order: 

 OH > NH, > halogens > CH,. 



The question now aiose how to expi-ess those velocities also in figures. 



Dr. Wii?AUT has done this for chlorine and methyl by determining 

 in what proportion the isomerides are formed in the nitration of 

 o-chlorotolueue. In this compound the positions 4 and 6 are occupied, 

 under the influence of methyl, by a nitro-group, the positions Sand 

 CHs 5 under the influence of chlorine. If now we determine 

 Qi the proportion in which the mononilro-chlorotoluenes 4-1-6 

 are present in regard to the isomerides 3 -|- 5 in the 

 nitration product, this is then also the proportion of the 

 substitution velocities caused by methyl and chlorine, because they 

 can exert their action in this o-chiorotoluene independently of each 

 other; for the positions which are substituted under the influence 

 of methyl are different from those that are substituted under the 

 influence of chlorine. For this proportion was found CH, : CI = 1 : 1.475. 



Dr. VAN DEN Arend had previously determined the proportion in 

 which the nitro-p-chlorotoluenes are formed in the nitration of p-chloro- 

 toluene. If now, with the above mentioned ratio, w^e calculate the 

 relative quantities, those calculated figures appear to agree approxi- 

 mately with the obser\'ed ones. 



These researches, carried out in my laboratory, have now been 

 continued, partly by Dr. Heineken, so as to determine also the ratios 

 of the halogens. The method followed previously for the quantitative 

 determination of the isomerides, namely by means of the solidification 

 curves, could, however, not be applied here as the two nitro-p- 

 chlorobroinobenzenes give a continuous series of mixed crystals and 

 because it was to be expected, on account of the fact that the 

 properties of the nitrodihalogen benzenes present a strong mutual 

 resemblance, that this would occur in other cases also. 



Hence, for the quantitative determination of the isomerides present 

 in the nitration mixtures, we made use of the property that a halogen 

 in nitrohalogen benzenes is taken from the nucleus by Na-methoxide 



