Ionization Constants of the Six Dichloroanilines and the Six Dichlorophenols in Aqueous Solution at 25 °C

The thermodynamic ionization constants of the six dichloroanilines and the six dichlorophenols in aqueous solution at 25 °C have been determined by the spectrophotometric method. The pK values found are recorded in table 3. An approximately linear relation is found to exist between the pK(A) value of a dichloroaniline and the pK(P) value of the corresponding dichlorophenol. The relation is [Formula: see text] This equation yields pK(A) values which differ from the observed by not more than 0.06 pK unit and, on the average, by 0.03 pK unit; it applies even when both substituents are in the ortho position.