Abstract
The kinetics of complexation between various charged species of the ligand 4,5-dihydroxybenzene-l,3-disulfonic acid (“tirón”) and the divalent metal ions of nickel, cobalt, and magnesium have been investigated by the temperature-jump method. The complex formation rate constants for the —3 species of tirón and the divalent metal ions of nickel, cobalt, and mag- nesium were determined at a pH of 9.00 and at 20°. The second-order rate constants for the association of the —2 tirón species and the divalent metal ions of nickel and cobalt were determined at a pH of 4.66 and at 20°. In each case the stability of the metal complex decreases by several orders of magnitude with increasing ligand protonation; however, the association rate constant changes only by an order of magnitude. The large decrease in complex stability with increasing protonation is due to a large increase in the dissociation rate constant.