Oxidation of benzyl alcohols to ketones and aldehydes by O3 process enhanced using high-gravity technology

Abstract

Abstract In this study, a practical process for ozonization of benzyl alcohols to ketones and aldehydes in a rotating packed bed (RPB-O3) reactor has been developed. Using 1-phenylethanol as a model reactant, the performance of RPB-O3 process in different solvents has been compared with the commonly used stirred tank reactor (STR-O3). Ethyl acetate was the optimum solvent for the conversion of 1-phenylenthanol to acetophenone in RPB-O3 process, with 78% yield after 30 min. In a parallel STR-O3 experiment, the yield of acetophenone was 50%. Other experimental variables, i.e. O3 concentration, reaction time, high-gravity factor and liquid flow rate were also optimized. The highest yield of acetophenone was obtained using O3 concentration of 80 mg·L−1, reaction time of 30 min, high gravity factor of 40 and liquid flow rate of 120 L·h−1. Under the optimized reaction conditions, a series of structurally diverse primary and secondary alcohols was oxidized with (19%–92%) yield. The ozonization mechanism was studied by Electron Paramagnetic Resonance (EPR) spectroscopy, monitoring the radical species formed upon self-decomposition of O3. The characteristic quadruple peak with the 1:2:2:1 intensity ratio that corresponds to hydroxyl radicals (·OH) was observed in the electron paramagnetic resonance (EPR) spectrum, indicating an indirect oxidation mechanism of alcohols via ·OH radical.