A catalyst-free and highly efficient approach to ozonation of benzyl alcohol to benzoic acid in a rotating packed bed

Abstract

Abstract In this study, benzyl alcohol was ozonized to benzoic acid in a rotating packed bed (RPB-O3) by a catalyst-free and highly efficient approach, which is the most significant transformations in synthetic organic chemistry, and the RPB-O3 process was compared with the process in a stirred tank reactor (STR-O3). The results show that the RPB-O3 process produces more benzoic acid (64%) than the STR-O3 process (28%) in 30 min. The effects of different operating conditions of high gravity factor, liquid flow rate, solvent and reaction time on the yield of benzoic acid in the RPB-O3 process were investigated. The results reveal that the optimal yield is obtained using ethyl acetate as the solvent at a high gravity factor of 40, a liquid flow rate of 120 L/h, and a reaction time of 60 min. Under the optimal conditions, p-substituted benzoic acid is obtained in good to excellent yields (82–98%) in 60 min. Electron paramagnetic resonance (EPR) was performed to characterize radical species formed by the self-decomposition of ozone in nonaqueous solvents, and DMPO-·OH, DMPO-O2·ˉ and DMPO-·CH(OH)Ph were found. The possible ozonization mechanism is proposed based on the EPR results.