98 Reports on the state oe science. 



chloride. Blanksma showed for acetylchloroaminobenzene that the 

 reaction was of the first order, and the velocity proportional to the 

 square of the concentration of the hydrogen chloride. Assuming the 

 conversion to be due to the setting free of chlorine and anilide followed 

 by direct chlorination, then 



<7[chloroanilide] Jdt = /.• n [anilide][ClJ. 



But 



K[anilide][Cl 2 ] = [chloroamineftHCl] 1 ; 

 hence 



^[chloroanilide] I it = Z-n[chloroamine][HClp/K 



[chloroamine] equals approximately the chloroamine originally present, 

 when the amount of anilide and chlorine in the system in equilibrium 

 is very small, as in the case in media below 50 per cent, acetic acid. 

 [HC1] is constant. Hence 



<?[chloroanilide] / dt = A'n.Const.fchloroamine] /K = Zf'[chloroamine], 



a reaction of the first order. 



But it still remains to suggest causes for the extraordinary 

 reactivity of anilides towards substituting agents and their rigid 

 adherence to the ortho-para law. The hypothesis may be put forward 

 that the constitution of anilines and anilides, similar to but in a less 

 degree than p-nitrosophenol, permits of the passage into a dynamic 

 isomeride of quinonoid structure, which is accompanied by the wander- 

 ing of hydrogen of the imino group to the o- or p-position. It is this 

 isomeride which is reactive. The almost exclusive occurrence of 

 o- and p-quinonoid compounds accounts for the position taken up by 

 the substituting group. Just as with the hypothetical intermediary 

 complex, a change of structure of the benzene nucleus is assumed; 

 but here the mobile hydrogen atom and not chlorine migrates. 



Further, this suggestion brings out the close analogy of the anilines 

 and anilides with the phenols, where there is little evidence for the 

 formation of compounds of the substituting agent with the oxygen, and 

 much other evidence for the occurrence of a quinonoid structure. 



This suggestion, on the other hand, relegates to the background 

 the attractive view of the part played by the latent valency of the 

 tervalent nitrogen, which permits of a ready means of primary union 

 between the substituting agent and the anilide. 



Fliirscheim 1 has attempted to account for the laws of substitution 

 in aromatic compounds by reference to latent or rather partial valencies 

 of certain of the carbon atoms in a monosubstituted derivative of 

 benzene; with certain substituents the attractions on the hydrogen 

 atoms in the o- and p-positions, and with others in the m -position, are 

 loosened, and hence more readily resubstituted. It is obvious that this 

 view is independent of intermediate compounds, and would harmonise 

 generally with the facts of chlorination as recorded in the foregoing. 



Recently Lowry 2 has discussed this subject, and has suggested 



1 Journ. Prakt. Chem., 1905, [2], 71, 497; ibid., 1907, [2], 76, 165* 

 8 Science Progress, 1909, 3, 616; 4, 213. 



