Ionic liquid-mediated catalytic oxidation of β-caryophyllene by ultrathin 2D metal-organic framework nanosheets under 1 atm O2

An ionic liquid (IL)-mediated facile method was established for the epoxidation of beta-caryophyllene with molecular oxygen using ultrathin (similar to 3-6 nm) 2D Cu-, Co- or Ce-based MOF nanosheets. Under the optimum conditions, high selectivity (92.4%) and excellent yield (86.7%) for beta-caryophyllene epoxide were obtained over ultrathin (similar to 5.5 nm) Cu-TCPP nanosheets (TCPP = tetrakis(4-carboxyphenyl)porphyrin) with the aid of [C(12)mim]Cl at 313 K and 1 atm O-2. Notably, a small amount of [C(12)mim]Cl (1-dodecyl-3-methylimidazolium chloride, 5.0 mol %) played pivotal roles in forming a favorable microenvironment in-situ, thus significantly improving the catalytic performances of above-mentioned Cu-TCPP nanosheets containing PVP stabilizer. Moreover, ultrathin Cu-TCPP nanosheets showed better stability during beta-caryophyllene transformation in the presence of amphiphilic [C(12)mim]Cl, as supported by TEM and XRD analyses. Importantly, the addition of TBHP (tert-butyl hydroperoxide, 13.0 mol %) initiator is also crucial for the aerobic oxidation of beta-caryophyllene via Cu-TCPP nanosheets/[C(12)mim]Cl/TBHP/O-2 nanosystem. Further insights into the synergistic effects and free radical mechanism were achieved by fluorescence, DRUV-Vis, UV-vis and XPS measurements.