The theoretical investigation of OH-induced degradation mechanisms of isoproturon
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ORIGINAL PAPER
The theoretical investigation of OH-induced degradation mechanisms of isoproturon Xiaohua Ren 1 & Ruilong Liu 1 & Shanshan Zhang 2 & Jinying Zhang 3 Received: 27 May 2020 / Accepted: 3 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Herbicides are widely applied in agriculture, which causes emerging concern for contaminating surface water and groundwater. The degradation of isoproturon, being a typical phenylurea herbicide, has been studied much with advanced oxidation processes. However, little information on the detailed degradation mechanism from the theoretical level is available. In the present work, the degradation mechanisms of OH-initiated reactions of isoproturon were studied at the MPWB1K/6-311+G(3df, 2p)//MPWB1K/6-31+G(d, p) level. The calculation results display that H-atom abstraction, ·OH addition, and ·OH substitution pathways are found for ·OH and isoproturon reactions. For H-atom abstractions, the results show that aliphatic H atoms are more easily abstracted by ·OH than the aromatic H atoms, and the pathway R6 has the lowest energy barrier of 6.65 kcal mol−1, indicating that H in the –CH3 group attached to the N2 atom could be most favorably abstracted. Six pathways for ·OH addition to the six sites of the phenyl ring are identified with low energy barriers, which are in good accordance with the fact that the additions of ·OH to the phenyl ring were the important steps from experimental results. For ·OH substitution reactions, two pathways with high activation energies are found, and the corresponding products have been also detected from previous experimental studies, suggesting that the substitution reactions could also occur. Keywords ·OH . H-atom abstraction . Addition . Substitution . Degradation mechanism
Introduction N,N-Dimethyl-N′-[4-(1-methylethyl)phenyl]urea, usually named isoproturon, belongs to phenylurea herbicides, which are widely applied in different regions of the world, such as China, Europe, and the USA [1]. Isoproturon is a systemic herbicide and mainly used for controlling annual grasses and broad-leaved weeds in cereals and wheat [2–5]. Due to its Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00894-020-04503-4) contains supplementary material, which is available to authorized users. * Xiaohua Ren [email protected] 1
School of Water Conservancy and Environment, University of Jinan, Jinan 250022, People’s Republic of China
2
Weifang University of Science and Technology, Weifang 262700, People’s Republic of China
3
Shandong Institute of Land Survey and Mapping, Jinan 250100, People’s Republic of China
extensive use in agriculture and relatively high solubility in water, isoproturon is one of the frequently identified pesticides in polluted groundwater, surface water, and effluents of wastewater treatment plants [4, 6–8]. Isoproturon is listed as one of the 33 priority substances which have considerable risk to or via the aquatic environment by the European Union [9]. Th
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