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| Kinetics and Mechanisms of Novel Sulfonylurea Herbicide Methiopyrisulfuron Hydrolysis |
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| KeyWord:sulfonylurea herbicide; methiopyrisulfuron（HNPC-C9908）; hydrolysis; mechanisms |
| Author Name | Affiliation | | OU Xiao-ming | ①National Engineering Research Center for Agrochemicals；②National United Engineering Laboratory of Bionic Pesticide Engineering Technology；③Hunan Province Key Laboratory for Agrochemicals, Hunan Research Institute of Chemical Industry | | BU Hai-yan | ①National Engineering Research Center for Agrochemicals；②National United Engineering Laboratory of Bionic Pesticide Engineering Technology；③Hunan Province Key Laboratory for Agrochemicals, Hunan Research Institute of Chemical Industry | | PEI Hui | ①National Engineering Research Center for Agrochemicals；②National United Engineering Laboratory of Bionic Pesticide Engineering Technology；③Hunan Province Key Laboratory for Agrochemicals, Hunan Research Institute of Chemical Industry | | TANG De-xiu | ①National Engineering Research Center for Agrochemicals；②National United Engineering Laboratory of Bionic Pesticide Engineering Technology；③Hunan Province Key Laboratory for Agrochemicals, Hunan Research Institute of Chemical Industry | | HUANG Ming-zhi | ①National Engineering Research Center for Agrochemicals；②National United Engineering Laboratory of Bionic Pesticide Engineering Technology；③Hunan Province Key Laboratory for Agrochemicals, Hunan Research Institute of Chemical Industry | | FU Qi-ming | ①National Engineering Research Center for Agrochemicals；②National United Engineering Laboratory of Bionic Pesticide Engineering Technology；③Hunan Province Key Laboratory for Agrochemicals, Hunan Research Institute of Chemical Industry | | LEI Man-xiang | ①National Engineering Research Center for Agrochemicals；②National United Engineering Laboratory of Bionic Pesticide Engineering Technology；③Hunan Province Key Laboratory for Agrochemicals, Hunan Research Institute of Chemical Industry | | YU Kuai | ①National Engineering Research Center for Agrochemicals；②National United Engineering Laboratory of Bionic Pesticide Engineering Technology；③Hunan Province Key Laboratory for Agrochemicals, Hunan Research Institute of Chemical Industry |
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| Abstract: |
| Methiopyrisulfuron（test code：HNPC-C9908）, chemical name：methyl 2-（4-methoxy-6-methylthio-pyrimidin-2-yl） carbamoylsulfamoyl benzoate, is a novel sulfonylurea herbicide researched and developed by Hunan Research Institute of Chemical Industry, which has been used for weed control in wheat. Hydrolysis kinetics and mechanisms of methiopyrisulfuron in the aqueous solutions were studied in the laboratory using HPLC and LC-MS. Results showed that the hydrolytic degradation of methiopyrisulfuron followed first-order kinetics, and the degradation of the herbicide was dependent on the factors such as pH, temperature, clay minerals and surfactants. In the range of pH 1~10, the hydrolysis rate of methiopyrisulfuron decreased slowly with the increasing pH value, and reached the lowest value at pH 7, and increased significantly after that, and reached the maximum at pH 10. The calculated half-lives of methiopyrisulfuron at pH 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 were 20.03, 25.48, 33.36, 36.10, 55.45, 64.78, 216.61, 169.06, 4.26 and 1.17 days, respectively. The hydrolysis rate of methiopyrisulfuron in the buffer solution of pH 5, 7 and 9 increased significantly with the increasing temperature. The average activation energy（Ea）, enthalpy（ΔH） and entropy（ΔS） was calculated as 310.86 kJ·mol-1, 308.37 kJ·mol-1 and 1.65×10-1 kJ·mol·K-1 at pH 5, 230.59 kJ·mol-1, 228.81 kJ·mol-1 and 2.22×10-2 kJ·mol·K-1 at pH7, and 148.67 kJ·mol-1, 146.17kJ·mol-1 and -5.13×10-2 kJ·mol·K-1 at pH 9, respectively, which is required for the hydrolytic degradation of the herbicide, indicating that the hydrolysis was largely driven by the activation entropy. There was less significant difference between the hydrolysis rate constant of methiopyrisulfuron in the sterilized water and non-sterilized water from pond water and rice fields, indicating that microorganisms in the water had little impact on hydrolysis of methiopyrisulfuron. The surfactant 0205 obviously promoted the hydrolysis of methiopyrisulfuron, but no obvious effect of surfactant EL-40 and NP-20 was found. Clay minerals such as bentonite slowed down hydrolysis of methiopyrisulfuron in the aqueous solution. Through the isolation and identification of hydrolysis products of methiopyrsulfuron in pH5, 7 and 9 solution by LC/MS, it was proposed that the major hydrolysis pathway of methiopyrisulfuron involved in the sulfonylurea bridge cleavage of the parent molecule to give the four main hydrolytic products such as 4-methoxy-6-（methylthio） pyrimidin-2-amine, 4-methoxy-6-（methylsulfinyl） pyrimidin-2-amine, methyl-2-sulfamoyl benzoate and methyl 2-sulfinyl benzoate. |
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