Solvent-free selective oxidation of alcohols with tert-butyl hydroperoxide catalyzed by dioxo-molybdenum (VI) unsymmetrical Schiff base complex immobilized on CoFe2O4@SiO2 nanoparticles

In the present paper, the catalytic activity of a dioxo-molybdenum (VI) unsymmetrical Schiff base complex immobilized on CoFe2O4@SiO2 core–shell nanoparticles (CoFe2O4@SiO2@[MoO2(salenac-OH)] where salenac-OH = [9-(2',4'-dihydroxyphenyl)-5,8-diaza-4-methylnona-2,4,8-trienato](-2)) was studied in the selective oxidation of alcohols using tert-BuOOH (TBHP, 70% aqueous solution) as an oxidant. In this catalytic system, the contribution of different solvents was investigated, and it was found that the various primary and secondary alcohols were oxidized to their equivalent aldehydes and ketones with good to excellent yields (64–97%) at ambient temperature under solvent-free conditions. Moreover, the effect of other essential factors such as the type of oxidant and the quantity of catalyst on the oxidation of benzyl alcohol was explored. Among different oxidants such as H2O2, urea/H2O2 (UHP), tert-BuOOH (TBHP) and NaIO4, tert-BuOOH was selected as oxygen donor, and the oxidation of benzyl alcohol required 50 mg (0.0135 mmol Mo) of catalyst to complete. The CoFe2O4@SiO2@[MoO2(salenac-OH)] catalyst can be conveniently removed from the reaction mixture by using an external magnet and reused four times without notable loss of its catalytic performance. Besides, comparing the X-ray diffraction (XRD) pattern, Fourier transform infrared (FTIR) spectrum, scanning electron microscopy (SEM) image, and energy-dispersive X-ray (EDX) analysis of the recycled catalyst with fresh catalyst showed no significant difference, proving that the catalyst structure remained intact after recovery.