DECOMPOSITION OF HYDROGEN-PEROXIDE CATALYZED BY VANADIUM(V) COMPOUNDS - THE PATHWAYS FOR THE FORMATION OF OZONE

Reactions of H2O2 in trifluoroacetic acid catalyzed by vanadium(v) compounds were studied. The system under study exhibits unusual behavior: along with oxygen, large quantitaties (10-15 %) of ozone are found in the products of hydrogen peroxide decomposition; difficultly oxidizable compounds (alkanes, arenes, and perfluoroalkenes) are oxidized under mild conditions. The rates of the oxidation of individual substrates are commensurable. However, when two compounds are simultaneously present in the reaction mixture, cyclohexane stops the oxidation of all of the other substrates, arenes suppress the oxidation of perfluoroolefins, and perfluoro-1-octene stops the consumption of internal perfluoroolefins. The effect of the oxidizable substrates on the amount of ozone evolved was studied. Based on the kinetic data obtained, a mechanism that involves the consecutive formation of several active complexes of vanadium(v) responsible for the oxidation of substrates and for the formation of ozone is suggested. In terms of the scheme suggested, the inner-sphere oxidation of the peroxo ligand by the coordinated peroxotrifluoroacetic acid affords a complex incorporating O-3(2-) as a ligand. The latter acts as the precursor of the ozone. A mathematical model that adequately describes the experimental data is proposed.