Abstract
The combination of relatively low-cost ionic liquids, simple copper salt, and terminal oxidant tert-butyl hydroperoxide provided an efficient and environmentally friendly approach to the preparation of ionone-like dienones. Six pyridinium ionic liquids were evaluated in allylic oxidation of α-ionone and β-ionone. The 60%–70% yields of 3-oxo-α-ionone were obtained with 0.02–0.20 mmol of CuCl 2·2H 2O as catalyst, 3–5 mmol of tert-butyl hydroperoxide as oxidant and 1 g of [Bpy]PF 6 as solvent for 4–20 h at 60°C. The facile recovery and recycle of catalyst were also achieved. More significantly, peculiar phase behaviors of [Bpy]PF 6 and [Epy]PF 6 offered the catalytic system advantages of homogeneous reaction and heterogeneous separation. Scanning electron microscope (SEM) images of [Bpy]PF 6 provided evidences for the behaviors. Transmission electron microscope (TEM) micrographs showed copper salt nanoparticles catalyst formed and stabilized in pyridinium ionic liquids.
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