ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 18, Number 4
JKCSEZ 18(4)
August 20, 1974 

Isotopic experiments using H2O18 on the oxidation of V(Ⅲ) in acid perchlorate by molecular oxygen were performed in the range pH 1.0 to 3.0. At pH < 2, where a rate equation of the form -d[V(Ⅲ)]/dt = k1[O2][V(Ⅲ)]/[H+] is adequate, the tracer study clearly indicated that all the product vanadyl ion's (VO2+) oxygen originated from the molecular oxygen. At pH > ~2, where a different rate expression of the form -d[V(Ⅲ)]/dt = k1[O2][V(Ⅲ)]2/[H+]2 is required, the isotopic experiment showed that half the vanadyl oxygen originated from the molecular oxygen. Considering the results of the isotopic study, a mechanism for the V(Ⅲ)-O2 reaction at pH < ~2, may be suggested as follows: VOH2+ + O2 → V(O2)OH2+(rate determining step), V(O2)OH2+ + VOH2+ → 2VO2+ + H2O2 The tracer results at pH > ~2 imply that the rate determining step may be V2(OH)24+ + O2 → 2VO2+ + H2O2 followed by V2(OH)24+ + H2O2 → 2VO2+ + 2H2O after establishing the equilibria V3+ + H2O ↔ VOH2+ + H+, and 2VOH2+ ↔ V2(OH)24+