ON THE TRANSFORMATION OF AROMATIC NITROAMINES. 107 
hydrolysed by water in the acetic acid medium, the initial concentration 
was arrived at by deducting an amount equivalent to the water from 
the anhydride used. 
The experiments have led to some very interesting results :— 
1. The reaction is of the second order; the value of the expression, 
1 x 
t ‘ (a—2) 
2. The speed is approximately proportional to the concentration of 
the catalyst when the concentrations of the aniline and anhydride are 
kept constant. 
3. A very remarkable effect was produced by variation of the 
concentration of the aniline, when anhydride and catalyst are kept 
constant. It would be expected that the speed of acetylation would fall 
on decreasing the concentration of the aniline; on the contrary, how- 
ever, the speed increases. A comparison of experiments A and B 
shows that on halving the concentration of the aniline the speed is 
roughly doubled. The most obvious explanation of the observation 
is that the acid catalyst is partly combined with the aniline. Such a 
balanced action would follow the equation of equilibrium :— 
[Aniline] [H,SO,] = K [anilinium salt}. 
[H,SO,]= K {anilinium salt] 
[aniline ] 
, is approximately halved by doubling the dilution. 
Since the proportion of the acid, and therefore of the salt, is very 
small in comparison with that of the aniline in these systems, the 
concentration of the acid is roughly inversely proportional to that of 
the aniline. The concentration of the free acid (or perhaps acid salt) 
is the dominant factor in the reaction, and hence the effect (if there 
be one) of the decrease of the aniline is completely concealed. This 
suggestion 1s made more probable by the effect of simultaneous reduc- 
tion of the concentration of both acid and aniline; the velocity of acety- 
lation is scarcely changed (Exp. C). It appears, then, that the speed 
of acetylation is independent (within certain limits) of the concentra- 
tions of the acid and aniline, provided that these quantities remain in 
the same ratio. 
The action of the catalyst probably lies, as has been frequently 
suggested, in producing an ‘ active modification’ of the acetic anhy- 
dride, which alone reacts with the aniline. The evidence, so far as it 
goes, points to the reaction of the anhydride and catalyst being momen- 
tary, whilst that of the ‘ active ’ form and the aniline is a time reaction. 
Too much stress cannot be put upon the fact that the reaction was of 
the second order, for the excess of anhydride was considerable. The 
combination of the acid with the aniline, moreover, obscures the issue, 
and renders a decision difficult with an acid catalyst. 
A complete account of this research will be published in one of 
the usual chemical journals. 
