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

• Published in: Journal of molecular catalysis. A, Chemical Vol. 227; no. 1; pp. 37 - 45
• Main Authors: Raj, N.K. Kala, Ramaswamy, A.V., Manikandan, P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-03-2005; Elsevier
• Subjects: 2,3-Epoxy norbornane; Aq. H 2O 2; Catalysis; Chemistry; Epoxidation; EPR; Exact sciences and technology; General and physical chemistry; NMR; Norbornene; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Urea–H 2O 2 adduct; UV–vis; Vanadium-substituted phosphomolybdic acid; UV–vis; NMR; Vanadium-substituted phosphomolybdic acid; Aq. H 2O 2; EPR; 2,3-Epoxy norbornane; Epoxidation; Norbornene; Urea–H 2O 2 adduct; Solvent effect; Aq. H2O2; Urea-H2O2 adduct; Hydrogen peroxide; EPR spectrometry; Transition metal; NMR spectrometry; UV-vis; Vanadium Compounds; Heteropolyacid; Urea; Ureas; Oxidation; Catalyst
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2004.10.005

Oxidation of norbornene has been carried out over mono-, di- and tri-vanadium-substituted phosphomolybdic acid catalysts with aqueous hydrogen peroxide (aq. H
2O
2) 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
°C, 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. H
2O
2 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. H
2O
2 reaction; however, 2,3-epoxy norbornane was the main product with >97% selectivity. Thus, the overall yield was 66.9% at 60
°C after 4
h. The high selectivity with UHP is attributed to the controlled release of H
2O
2, 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.
Oxidation of norbornene was carried out over vanadium-substituted phosphomolybdic acid catalysts with different oxidants. With aqueous hydrogen peroxide (aq. H
2O
2) 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. H
2O
2 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. H
2O
2. 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.
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