On the physicochemical characterization of 5-amino-1-aryl-1H-tetrazoles: Electronic molecule parameters from the thermal isomerization into 5-arylamino-1H-tetrazoles

The known thermal isomerization of 5-amino-1-aryl-1H-tetrazoles (A) into co rresponding 5-arylamino-1H-tetrazoles (HB) was used to derive physicochemic al parameters characterizing the electronic substituent effect on isomerism and dissociation equilibria, For a series of 26 tetrazoles A as starting m aterials the equilibrium constants (pK(i)) of isomerization in boiling ethy lene glycol at 197 degrees C and the dissociation constants (pK(a)) of the NH-acidic tetrazoles HB were determined by potentiometric titration of rapi dly cooled equilibrium mixtures in water and ethanol/water with KOH at 25 d egrees C, The pK values are closely correlated with Hammett's electronic su bstituent constants sigma and can be used as electronic molecule parameters in QSAR or QSPR (QSAR = quantitative structure-activity relationship; QSPR = quantitative structure-property relationship) studies.