The ionization constants of 2‐substituted 4,6‐diamino‐s‐triazines: The applicability to the hammett and taft equations

The ionization (or basicity) constants (pKb) were determined for many 2‐substituted 4,6‐diamino‐s‐tri‐azines (I) by means of the electrometric titration. I includes 2‐alkoxy or aryloxy‐(Ia), 2‐alkyl‐ or 2‐aryl‐(Ib), and 2‐alkylamino‐ or 2‐arylamino‐4,6‐diamino‐s‐triazines (Ic). For the series with the same alkyl or aryl group, the order of the basicity was found to be Ic < Ib < Ia. A study was made of relationships between the pKb, values of I, and the substituent constants, σp, σm, σp+, σm+, σpO, σmo, σI, σn, and σ*. The Hammett relationships were observed between the pKa values of I, and the substituent constants σm, (or the combination ones, [0.97σm + 0.03σp] as well as another [0.77σI + 0.23σR]). The Taft relationships were also found between the pKa values of Ia, Ib, and Ic and the constants σ*, respectively. Furthermore, in the case of Ic a linear relationship was observed between the pKa values and Σσ8.