Tetrazoles as Carboxylic Acid Analogs 151 



inductive effect noted when the alkyl groups were attached directly 

 at the 5-position is not transmitted by the amino nitrogen. 5-Amino- 

 and 5-dimethylaminotetrazole have the same apparent acidic dissocia- 

 tion constants. Neither steric nor inductive effects are apparent in 

 this instance. Other groups which may exert little steric influence 

 likewise have essentially no effect on the magnitude of the dissociation 

 constant. Thus, 5-dibenzylamino-, 5-benzylmethylamino-, and 5-dial- 

 lylaminotetrazole are as strongly acidic as 5-aminotetrazole and 5- 

 (liniethylaminotetrazole (Table 3). On the other hand, there is a 

 marked decrease in acid strength on going from 5-dimethylaminotetra- 

 zole to 5-diethylamino-, 5-diisopropylamino-, 5-di-n-butylaminotetra- 

 zole, and other larger dialkylaminotetrazoles. Since the inductive 

 effects of most alkyl groups are comparable, their steric influence 

 apparently predominates. A similar decrease in acid strength accom- 

 panies the change from 5-benzylmethylamino- to 5-benzylethylamino- 

 tetrazole. There is a nice correspondence in the occurrence of a steric 

 effect in this group with that observed in certain hindered carboxylic 

 acids and described by Newman in terms of the "six-number." 9 Those 

 compounds having the largest six-number are the weakest acids 

 (Table 4). 



Table 4. Steric Factors and Apparent Dissociation Constants of Some 

 5-Dialkylaminotetrazoles 



H 



/ 

 R 2 N— C— N 



\ 



X 



N— N 



1! K a X lu 8 Six-Number 

 CH 3 38 



C 2 II 6 1 1 6 



C 3 H 7 -iso 6 12 



C 4 H 9 -n 10 6 



Apparently other factors play a part in determining the acid strength 

 of the 5-monoalkylaminotetrazoles. 5-Methylaminotetrazole is a 

 weaker acid than the corresponding dimethylamino compound. A 

 similar relationship exists between 5-benzylamino- and 5-dibenzyl- 

 aminotetrazole. On the other hand in 5-ethylaminotetrazole, where 

 the steric effect of a single ethyl group should be appreciably less than 



