Oxidation of norbornene over vanadium-substituted phosphomolybdic acid catalysts and spectroscopic investigations

Oxidation of norbornene was carried out over vanadium-substituted phosphomolybdic acid catalysts with different oxidants. With aqueous hydrogen peroxide (aq. H2O2) the conversion was 70% and epoxide selectivity was 58% at 60 °C. With other oxidants like urea-hydrogen peroxide adduct and TBHP the selectivity for epoxide was >96%. Lower selectivity of epoxide with aq. H2O2 is attributed to the simultaneous formation of other products, norborneols and 2-norbornanone due to an acid-catalyzed reaction, where acidity comes from the decomposition of aq. H2O2. The high selectivity with the other oxidants is attributed to the controlled release of peroxides and low acidic nature. Based on spectroscopic results, a mechanism for the norbornene oxidation is believed to be proceeding via V(5+)-peroxo and V(4+)-superoxo intermediates.