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- Catalytic oxidation of cyclohexane with hydrogen peroxide and a tetracopper(II) complex in an ionic liquidPublication . Da Costa Ribeiro, Ana Paula; Martins, Luisa; HAZRA, SUSANTA; Pombeiro, ArmandoThe catalytic peroxidative oxidation (with H2O2) of cyclohexane in an ionic liquid (IL) using the tetracopper(II) complex [(CuL)2(μ4-O,O′,O′′,O′′′-CDC)]2·2H2O [HL = 2-(2-pyridylmethyleneamino)benzenesulfonic acid, CDC = cyclohexane-1,4-dicarboxylate] as a catalyst is reported. Significant improvements on the catalytic performance, in terms of product yield (up to 36%), TON (up to 529), reaction time, selectivity towards cyclohexanone and easy recycling (negligible loss in activity after three consecutive runs), are observed using 1-butyl-3-methylimidazolium hexafluorophosphate as the chosen IL instead of a molecular organic solvent including the commonly used acetonitrile. The catalytic behaviors in the IL and in different molecular solvents are discussed.
- Highly selective cyclohexane oxidation catalyzed by ferrocene in ionic liquid mediumPublication . Martins, Luisa; Da Costa Ribeiro, Ana Paula; Pombeiro, ArmandoBackground: Although economically very important in view of the significance of the oxidized products for the manufacture of adipic acid and caprolactam (precursors to polyamides widely used in several industries), the current cyclohexane oxidation industrial process leads to very low conversions (ca. 4%) to assure a reasonable selectivity (ca. 85%). Therefore, there is an urgent need to develop sustainable selective cyclohexane oxidation chemistry, which is the main objective of this work. Methods: The partial oxidation of cyclohexane by aqueous tert-butyl hydroperoxide (TBHP, 70% aq. sol.) in phosphonium ionic liquid medium [P6.6.6.14][DCA] and in the presence of catalytic amounts of ferrocene was investigated. The reaction proceeded during 2 h at room temperature. Results: It was found that TBHP, under the above conditions, oxidizeD cyclohexane with high selectivity (> 98%), yielding mainly cyclohexanone (up to 16%, based on the substrate) with total TOFs up to 1 x 104 h-1. Conclusion: The combination of a commercial iron-complex catalyst (ferrocene) and well-adjusted unconventional reaction conditions led to a highly selective, fast and reusable catalytic system for the mild oxidation of cyclohexane. Moreover, the found [Fe(C5H5)2]/[P6.6.6.14][DCA] catalytic system can be of significance to produce polyamide 6.