Kinetics of oxidation of iron(II) by vanadium(V) under the conditions where VO2+ and decavanadate coexist

Abstract

The kinetics of the reaction between iron(II) and vanadium(V) have been investigated in the pH range 2.6–4.2 where decavanadates and VO2+ coexist in equilibrium. Under these conditions, the observed kinetic pattern is radically different from the one reported for the reaction in strong acid medium. In the pH range employed, the reaction rate is not appreciably altered by variation in the stoichiometric vanadium(V) concentration due to the operation of the equilibrium between the reactive species, VO2+, and the unreactive species, decavanadates. The reaction, however, obeys first‐order kinetics with respect to Fe(II). In the presence of salicylic acid, which imparts considerable reactivity to iron(II) by reducing the reduction potential of iron(III)/iron(II) couple by forming a stronger complex with iron(III) than iron(II), the kinetic results provide evidence for the participation of decavanadates in the electron transfer. The mechanism under both conditions is discussed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 535–541, 2000

Understanding the Reduction Kinetics of Aqueous Vanadium(V) and Transformation Products Using Rotating Ring-Disk Electrodes

“…This structure was not available in VO 2 + , V 4 and HVO 4 2– . In addition, V 10 underwent much smaller configuration change than the other three species, during the reduction process that also contributed to its largest intrinsic rate constants (eqs –). ,, Prior study also showed that decavanadate was more active to stimulate NADH oxidation than metavanadate (V 4 -dominated) because of fast electron-transfer kinetics in cage-like superstructure . The dioxo ligands in VO 2 + and the cyclic structure of V 4 likely made vanadium atoms more intrinsically reducible than that in HVO 4 2– .…”

“…Prior studies showed that V 10 was partially reduced by ascorbate and Fe(II) via a twoelectron-transfer process and maintained its cage-like original structure. 29,30,42 The EC-calculated electron-transfer number of V 10 reduction was smaller than two (n = 1.5) because the reduction current was likely impacted by strong interaction between vanadium reduction products and electrode surface. This was supported by a decrease of reduction current at high over-potentials, i.e., the difference between applied potential and onset reduction potential (Figure 3B).…”