The degradation mechanism of sulfamethoxazole under ozonation: a DFT study.
Sulfamethoxazole (SMX), a kind of antibiotic, remains in the environment and threatens public health. Ozone as a strong and green oxidant was widely used for selective oxidation degradation of residual SMX. However, it is hard to elucidate the detailed oxidation mechanism through current experimental approaches. A theoretical study has been carried out herein for exploring possible ozonation pathways of SMX. Two reaction mechanisms, viz., direct addition (DA) and H atom transfer (HAT), are considered. The results show that the primary oxidation of aromatic rings (benzene or isoxazole rings) of SMX follows the DA mechanism, featuring an electrophilic addition. Whereas, the oxidation of amino and methyl groups of SMX follows the HAT mechanism. Following the proposed mechanisms, the primary oxidation products detected in previous experiments could reasonably be obtained according to the current calculations. More importantly, O3molecules as an electrophilic agent feasibly attack the moiety having a large orbital contribution to the highest occupied molecular orbital (HOMO) of sulfonamides. This result suggests that the primary ozonation site of sulfonamides could be theoretically predictable through the information of their frontier molecular orbitals. Meanwhile, a positive correlation between the O3-mediated HAT energy barriers and bond dissociation energies has been found for N-H and C-H bond oxidations.
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China. luoyi@dlut.edu.cn.
Hang
H
Yu
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China. luoyi@dlut.edu.cn.
Pu
P
Ge
Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China. jwchen@dlut.edu.cn.
Jingwen
http://orcid.org/0000-0002-5756-3336
J
Chen
Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China. jwchen@dlut.edu.cn.
Hongbin
H
Xie
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China. luoyi@dlut.edu.cn.
Yi
http://orcid.org/0000-0001-6390-8639
Y
Luo
D000900:Anti-Bacterial Agents / Q000737:chemistry*; D004785:Environmental Pollutants / Q000737:chemistry*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*; D013420:Sulfamethoxazole / Q000737:chemistry*
D000900:Anti-Bacterial Agents; D004785:Environmental Pollutants; D010126:Ozone; D013420:Sulfamethoxazole