Ionic liquid-modulated aerobic oxidation of isoeugenol and β-caryophyllene via nanoscale Cu-MOFs under mild conditions

Abstract

Novel synergistic systems based on Cu-1,3,5-benzenetricarboxylate and ionic liquid are developed for the convenient conversion of renewable olefins, isoeugenol and β-caryophyllene, under very mild conditions (i.e. 313 K and 1 atm O2). Using acidic ionic liquid [C4mim][HSO4] (5.0 mol%) as co-catalyst, Cu3(BTC)2-Lauric acid (LA) afforded high selectivity (95.8%) and excellent yield (86.3%) for vanillin methyl ketone during the aerobic oxidation of isoeugenol. In comparison, 91.1% selectivity for vanillin together with 28.9% conversion of isoeugenol was obtained over Cu3(BTC)2-LA in the presence of amino acid ionic liquid, [C4mim][Ala]. Additionally, 91.3% selectivity and 86.5% yield for β-caryophyllene epoxide were provided by Cu3(BTC)2-LA with the aid of neutral [C4mim]Cl (5.0 mol%), indicating the importance of different types of ILs in tuning the microenvironments of designed Cu3(BTC)2-LA nanosystems. Simultaneously, Cu3(BTC)2-LA/IL showed superior stability during above-mentioned transformations, as verified by TEM, FT-IR and XRD analyses. Insights into the synergistic free radical routes were supported by fluorescence and DRUV-Vis characterizations.