Acid Dissociation Constants of 1-(p-Substituted phenyl)-1, 3-butanedion es

Abstract

The acid dissociation constants of 1-(p-substituted phenyl)-1, 3-butanediones (p-XC₆H₄COCH₂⋅COCH₃ X=NO₂[1], COOH[2], COOCH₃ [3] Br[4], Cl[5] H [6], NHCOCH₃ [7] CH₂H₅[8], CH₃ [9], OCH₃[10], OH [11] and NH₂ [12]) were determined by a potentio metric titration in dioxane-water (3: 1 v/v) at 25±0.2°C. The ionic strength of the solutions was adjusted at 0.1 with potassium nitrate. The pK_do. of enolic proton increased in the order of [1] (9.26)<[2] (9.69)<[2] (2.77)<[4]=[5] (10.11)<[7] (10.47)<[6] (10.53)<[8]=[9](10.78)<[10] (10.93)<[11](11 08)<[12](11.57). It was found that the basicity of these compounds increases as the substituent becomes more electron-donative, and that the intramolecular hydrogen bond is strengthened as the basicity increases.