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

TitleOxidation of norbornene over vanadium-substituted phosphomolybdic acid catalysts and spectroscopic investigations
Publication TypeJournal Article
Year of Publication2005
AuthorsRaj, NKK, Ramaswamy, A, Manikandan, P
JournalJournal of Molecular Catalysis A-Chemical
Date PublishedMAR
Type of ArticleArticle
Keywords2, 3-epoxy norbornane, aq. H2O2, epoxidation, EPR, NMR, norbornene, urea-H2O2 adduct, UV-Vis, vanadium-substituted phosphomolybdic acid

Oxidation of norbornene has been carried out over mono-, di- and tri-vanadium-substituted phosphomolybdic acid catalysts with aqueous hydrogen peroxide (aq. H2O2) as an oxidant in different solvents. Monovanadium-substituted phosphomolybdic acid catalyst was found to be better than other catalysts for the above reaction and acetonitrile was the suitable solvent. At the optimum temperature of 60 degreesC, the norbornene conversion was 70% and the selectivity for 2,3-epoxy norbornane was 58%. The side products were norborneols and 2-norbornanone. The lower selectivity of 2,3-epoxy norbornane with aq. H2O2 is attributed to the simultaneous formation of other products, norborneols and 2-norbornanone. The norborneols are formed from norbornene by acid-catalyzed reaction. Other oxidants like urea-hydrogen peroxide adduct (UHP) and tert-butyl hydrogen peroxide (TBHP) were also tested for norbornene oxidation reaction. With UHP, the conversion was almost same (69%) as that of aq. H2O2 reaction; however, 2,3-epoxy norbornane was the main product with >97% selectivity. Thus, the overall yield was 66.9% at 60 degreesC after 4 h. The high selectivity with UHP is attributed to the controlled release of H2O2, absence of water and less acidic nature of UHP. With TBHP the selectivity for the epoxide was >96%; however, the conversion was low (27%). A mechanism for the norbornene oxidation is believed to be proceeding via V(5+)-peroxo and V(4+)-superoxo intermediates. NMR, EPR and UV-vis spectroscopic techniques were employed to understand the reaction intermediates and reaction pathways. (C) 2004 Elsevier B.V. All rights reserved.

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Catalysis and Inorganic Chemistry