Tetrazoles as Carboxylic Acid Analogs 



143 



pounds built up around it. In a series of 5-alkyltetrazoles the apparent 

 acidic dissociation constants were variously from one-tenth to one-half 

 as large as those of the correspondingly substituted carboxylic acids. 

 A few examples are cited in Table 1. It will be noted that the dissocia- 



Tahle 1. 



Apparent Dissociation Constants of 5-AlkyltetrazoIes and 

 Aliphatic Carbovylic Acids 



R 

 H 

 CH 3 



C 2 H 5 



C3H7-" 



CsHv-iso 



C 4 H 9 -n 



CiHg-iso 



C5H11-W 



R~CN 4 H * 



K X 10 fi at 25' 



16.2 



2.74 

 (2.43) t 



2.5(3 



2.47 



2.80 

 (2.38) % 

 (2.45) t 

 (2.22) t 



R— C0 2 H | 



A' X 10 s at 25' 

 171.2 

 17.5 



13.3 



15 



13.8 



13.8 



16.7 



13.2 



* Apparent dissociation constants were determined by potentiometric titra- 

 tion in aqueous solution at 25°C. unless otherwise indicated. 2 



f Constants obtained from conductivity data in aqueous solution. 6 

 J Apparent dissociation constants determined by potentiometric titration in 

 25% (by weight) methanol at 25°C. 2 



tion constants are influenced in roughly the same manner by the nature 

 of the alkyl substituent in both series. 



The acidity of tetrazole itself is readily explained on the basis of the 

 resonance concept, i.e., the resonance stabilization of the tetrazolyl 

 anion formed upon dissociation of the proton attached to the ring 

 nitrogens (scheme IV). Similarly, the acidity of the carboxylic acids 



HN- 



I 

 N 



\ 



-CH 



II 



N 



H+ + 



'N 



(IV) 



has been attributed to resonance stabilization of the carboxylate ion 

 (scheme V). 



