Affinities of Poly basic Acids. 



29 



In view of the relations which have already been brought 

 out, it is of great interest to compare the constants pf 

 tetracarboxylic acids with those of the corresponding 

 dicarboxylic acids. The only cases which have apparently 

 been investigated hitherto are the dimethyl and diethyl 

 derivatives of pentanetetracarboxylic acid ; in each case as 

 Walker 1 has pointed out, the affinity of the acid is 

 enormously increased by the close proximity of the two 

 carboxylic groups at either end of the molecular chain. 



Dimethyl ... 

 Diethyl ... 



Pimelic Acid. 



Pentanetetracarboxylic Acid. 



Ratio. 



•00339 

 ■00345 



°'37 



2*1 



I ; 109 

 1:608 



The new dialkyl-derivatives of adipic acid and of butane- 

 tetracarboxylic acid, which the author has described else- 

 where, are now in the hands of Dr. J. Walker, and the 

 determination of their affinity constants will be awaited 

 with interest. 



In view of the various evidences which have been adduced 

 of the strengthening influence of one group upon another, 

 the facts referred to in the Introduction appear somewhat 

 less anomalous. In the tetracarboxylic acids referred to 

 of the general formula 



HOOC 

 HOOC 



CR-CH 2 -CH 2 -CR 



1 



< 



COOH 

 COOH 



there is that juxtaposition of acid groups which we have 

 seen so enormously increases the affinity of the acid, and 

 in accordance with this they have a well-marked acid 

 character. So soon, however, as the dibasic salt 



1 Walker, loc. cit. 



