Abstract
The stopped-flow technique has been utilized in kenctics studies of the formation of 1:1 complexes between vanadium(V) anions and EDTA (H4Y) as well as 1,2-dihydroxyanthraquinone (H2A). These studies have been conducted at 25° in weakly alkaline media at an ionic strength of 0.5 M (NH4C1). Reaction schemes for formation of the 1:1 complexes which account for the observed hydrogen ion dependences of the forward rate constants are presented. The rate constants for complex formation are essentially independent of the identity of the complexing ligands used in this study and agree with the previously determined rate constant for vanadate dimerization. The experimentally determined rate constants for complexation of V02(0H)2- and V02(OH)32- by H2Y2- are (2.34 ± 0.05) X 104 and (2.4 ± 0.1) X 10s M~l sec-1, respectively. For complexation of V02(OH)2- and V02(OH)32- by HA-, rate constants of (2.28 ± 0.08) X 104 and (1.2 ± 0.3) X 103 M-1 sec-1, respectively, were determined. The value of the stability constant for the HA--V02(OH)2- complex was found to be (1.0 ± 0.2) X 104 M.