Hydrodefluorination and hydrogenation of fluorobenzene under mild aqueous conditions

Rebekka Baumgartner, Kristopher McNeill

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

Fluorinated organic compounds are increasingly used in many applications, and their release to the environment is expected. It is therefore important to find suitable methods for degradation of fluorinated compounds under environmentally relevant conditions. In this study, a simple heterogeneous rhodium-based catalytic system (Rh/Al2O3 and H 2) for hydrodefluorination and hydrogenation of fluorobenzene under mild aqueous conditions (1 atm of H2, ambient temperature) was developed and the underlying reaction mechanism was investigated. Fluorobenzene degraded rapidly (t1/2 ≈ 0.2 h) to form cyclohexane and fluoride (F-) as the stable end products, with benzene and cyclohexene observed as intermediates. Cyclohexadiene intermediates were not observed but were expected to form during the hydrogenation of benzene. Three postulated but unobserved fluorinated intermediates were subjected to the catalytic reaction conditions, and it was concluded that they most likely do not form during the fluorobenzene degradation reaction. Isotope labeling experiments showed that the unsaturated intermediates undergo rapid and reversible hydrogenation/ dehydrogenation under the reaction conditions and also that fully saturated compounds are unreactive in the catalytic system. Both molecular hydrogen and water were sources of hydrogen in the final cyclohexane product. Kinetic fitting indicated that sorption/desorption of fluorobenzene onto the catalyst surface plays an important role in the mechanism.

Original languageEnglish (US)
Pages (from-to)10199-10205
Number of pages7
JournalEnvironmental Science and Technology
Volume46
Issue number18
DOIs
StatePublished - Sep 18 2012

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