Abstract
The protonation constants for 2,4,6‐tri(2‐pyridyl)‐1,3,5‐triazine (TPTZ), a well known extractant in partitioning of An(III)/Ln(III), were calculated from the solubility of TPTZ in aqueous solutions of varying acidity in equilibrium with either solid TPTZ or a nitrobenzene phase containing TPTZ. The values obtained are log K 1 = 3.55 ± 0.07, log K 2 = 2.72 ± 0.06. For the first time the existence of dimer form, H2TPTZ2 2+, has been proven and its stability constant, K 2,2, was found to be (1.79 ± 0.21) × 104 in the acidity range 2 < −log [H+] < 5.