A correlation of substituent effects with the acidity of aromatic tetrazolic acids

Abstract

The values of thermodynamic dissociation constants, K_a, have been determined for ortho-, meta-, and para-substituted 5-phenyltetrazoles (referred to as tetrazolic acids) and the effect of the nature of the substituent on the strength of the acids are discussed. The pK_a values, determined in 50%(v/v) ethanol–water and in 75%(v/v) dimethyl sulphoxide–water are correlated with the substituent constants σ_m and σ_p, which are equal to 0.64 and 0.56 respectively for the tetrazolyl substituent. To evaluate the contribution of the field and resonance effects, the K_a values were correlated with the î…� and constants based on the Swain–Lupton equation. The correlation, accomplished by using a two-parameter linear regression, gave î…�= 1.17 and =–0.13.