jo061909o_si_001.pdf (74.64 kB)
Imidazolium Ionic Liquids as Solvents for Cerium(IV)-Mediated Oxidation Reactions
journal contribution
posted on 2007-01-19, 00:00 authored by Hasan Mehdi, Andrea Bodor, Diána Lantos, István T. Horváth, Dirk E. De Vos, Koen BinnemansUse of imidazolium ionic liquids as solvents for organic transformations with tetravalent cerium salts as
oxidizing agents was evaluated. Good solubility was found for ammonium hexanitratocerate(IV) (ceric
ammonium nitrate, CAN) and cerium(IV) triflate in 1-alkyl-3-methylimidazolium triflate ionic liquids.
Oxidation of benzyl alcohol to benzaldehyde in 1-ethyl-3-methylimidazolium triflate was studied by
in-situ FTIR spectroscopy and 13C NMR spectroscopy on carbon-13-labeled benzyl alcohol. Careful control
of the reaction conditions is necessary because ammonium hexanitratocerate(IV) dissolved in an ionic
liquid can transform benzyl alcohol not only into benzaldehyde but also into benzyl nitrate or benzoic
acid. The selectivity of the reaction of cerium(IV) triflate with benzyl alcohol in dry ionic liquids depends
on the degree of hydration of cerium(IV) triflate: anhydrous cerium(IV) triflate transforms benzyl alcohol
into dibenzyl ether, whereas hydrated cerium(IV) triflate affords benzaldehyde as the main reaction product.
Reactions of ammonium hexanitratocerate(IV) with organic substrates other than benzyl alcohol have
been explored. 1,4-Hydroquinone is quantitatively transformed into 1,4-quinone. Anisole and naphthalene
are nitrated. For the cerium-mediated oxidation reactions in ionic liquids, high reaction temperatures are
an advantage because under these conditions smaller amounts of byproducts are formed.