TY - JOUR

T1 - Direct UV photodegradation of herbicide triclopyr in aqueous solutions: A mechanistic study

AU - Pozdnyakov, Ivan P.

AU - Snytnikova, Olga A.

AU - Yanshole, Vadim V.

AU - Fedunov, Roman G.

AU - Grivin, Vyacheslav P.

AU - Plyusnin, Victor F.

N1 - Funding Information: The financial support of the Russian Science Foundation (Grant RSF-NSFC ? 21-43-00004) is gratefully acknowledged. Authors also thank Ministry of Science and Higher Education of the RF for the access to LC-MS equipment. Publisher Copyright: © 2022 Elsevier Ltd

PY - 2022/4

Y1 - 2022/4

N2 - Mechanism of direct UV photolysis of pyridine herbicide triclopyr (TRI) was revealed by the combination of nanosecond laser flash photolysis, steady-state photolysis coupled with high resolution LC-MS and DFT quantum-chemical calculations. Both the detection of short-lived intermediates and the detailed identification of final products were done for the first time. The quantum yield of TRI photodegradation is about 4% at both UVC (254 nm) and UVB (308 nm) excitation. The primary stage is the heterolytic cleavage of C–Cl bond in dissociative triplet state of TRI with the formation of phenyl cation followed by a fast nucleophilic attack by a solvent molecule. The minor channel is the photohydrolysis leading to the formation of 3,5,6-trichloropyridin-2-ol. Primary photoproducts undergo secondary photolysis by the mechanism similar to initial TRI with the formation of products of acetic group elimination, sequential substitution of chlorine atoms to hydroxyl groups and, finally, oxidation and opening of the pyridine ring. Obtained results can be important for understanding the fate of pyridine herbicides in the processes of UVC disinfection and in natural waters under action of the sunlight.

AB - Mechanism of direct UV photolysis of pyridine herbicide triclopyr (TRI) was revealed by the combination of nanosecond laser flash photolysis, steady-state photolysis coupled with high resolution LC-MS and DFT quantum-chemical calculations. Both the detection of short-lived intermediates and the detailed identification of final products were done for the first time. The quantum yield of TRI photodegradation is about 4% at both UVC (254 nm) and UVB (308 nm) excitation. The primary stage is the heterolytic cleavage of C–Cl bond in dissociative triplet state of TRI with the formation of phenyl cation followed by a fast nucleophilic attack by a solvent molecule. The minor channel is the photohydrolysis leading to the formation of 3,5,6-trichloropyridin-2-ol. Primary photoproducts undergo secondary photolysis by the mechanism similar to initial TRI with the formation of products of acetic group elimination, sequential substitution of chlorine atoms to hydroxyl groups and, finally, oxidation and opening of the pyridine ring. Obtained results can be important for understanding the fate of pyridine herbicides in the processes of UVC disinfection and in natural waters under action of the sunlight.

KW - Heterolytic C–Cl bond cleavage

KW - Laser flash photolysis photodegradation

KW - Pyridine herbicides

KW - Triclopyr

KW - UV photolysis

KW - Water

KW - Water Pollutants, Chemical/analysis

KW - Glycolates

KW - Herbicides/chemistry

KW - Photolysis

KW - Kinetics

UR - http://www.scopus.com/inward/record.url?scp=85122637419&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/b2c923eb-aeb4-35ff-9255-79177399eb1f/

U2 - 10.1016/j.chemosphere.2022.133573

DO - 10.1016/j.chemosphere.2022.133573

M3 - Article

C2 - 35016955

AN - SCOPUS:85122637419

VL - 293

JO - Chemosphere

JF - Chemosphere

SN - 0045-6535

M1 - 133573

ER -