Kinetics and equilibria of the interaction of titanium(III) with oxalic acid
Abstract
Rate and equilibrium data have been determined for the complex-formation reactions of TiIII with oxalate in aqueous solution. In order to suppress the hydrolysis of TiIII, fairly high concentrations of hydrogen ion have been used. At 10.0 °C and ionic strength I= 1.0 mol dm–3(NaCl) the following stability constants have been obtained by spectrophotometry: Ti3++[C2O4]2–⇌[Ti(C2O4)]+, K1= 2.8 × 106 dm3 mol–1; [Ti(C2O4)]++[C2O4]2–⇌[Ti(C2O4)2]–, K2= 1.2 × 106 dm3 mol–1. The kinetics of the complex-formation reactions have been studied by the temperature-jump relaxation technique. At [H+]= 0.2–0.8 mol dm–3 complex formation occurs predominantly via reaction with the monoprotonated ligand. For the first step, Ti3++[HC2O4]– [graphic omitted] [Ti(C2O4)]++ H+, a rate constant of k1b= 3.9 × 105 dm3 mol–1 s–1 is evaluated and for [Ti(C2O4)]++[HC2O4]– [graphic omitted] [Ti(C2O4)2]–+ H+, k2b= 8.0 × 106 dm3 mol–1 s–1(10.0 °C, I= 1.0 mol dm–3). The kinetic data available indicate that substitution at the [Ti(OH2)6]3+ ion proceeds by an associative mechanism.