Kinetic Studies of the Acid Hydrolysis of Aquaoxo[N-(2-pyridylmethyl)iminodiacetato]vanadium(IV) and Aqua(nitrilotriacetato)oxovanadate(IV) in Aqueous Perchloric Acid Solution

Abstract

Abstract Acid hydrolysis of aquaoxo[N-(2-pyridylmethyl)iminodiacetato]vandium(IV) [VO(pmida)H2O], ([H+]=0.1–2.0 M, 1M=1 mol dm−3) and aqua(nitrilotriacetato)oxovanadate(IV) [VO(nta)H2O]−, ([H+]=0.2–2.0 M) has been studied by the stopped-flow method in aqueous perchloric acid solution at an ionic strength 2.0 (LiClO4). The pseudo first-order rate constant ko is dependent on the proton concentration. The rate formula is expressed by ko=(k1K1[H+]+k2K1K2[H+]2)⁄(1+K1[H+]+K1K2[H+]2). A simulation curve fitting treatment gave the figures: k1=0.02 and 0 s−1, k2=6 and 3000 s−1, K1=1.5 and 0.2 M−1, and K2=0.2 and 0.004 M−1 at 25 °C for [VO(pmida)H2O] and [VO(nta)H2O]−, respectively. These data indicate that the rate determining step corresponds to the dissociation of the second basal bond of the singly or doubly protonated oxovanadium(IV) complexes.