Theoretical and Experimental Approach for the Study of 2,4-Dichlorophenoxyacetic acid Photodegradation: C-O versus C-Cl Bond Dissociation Energies in the Gas Phase and Aqueous Medium

A theoretical, gradient-corrected Hartree-Fock-density functional theory (HF-DFT) approach was applied to the determination of the bond dissociation energy (BDE) for the photodegradation processes of the 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in the gas phase and in aqueous medium. According to the results of these calculations, the phenoxy C−O homolytic BDE value was found to be approximately two times lower than the corresponding C−Cl (2) and C−Cl (4) BDE ones, in both gas phase and under continuous solvation by water. An experimental study of the 2,4-D photodegradation reaction kinetics and photoproducts was also performed in water. At lower concentration, the formation of only two photoproducts (2-Cl- and 4-Cl-phenoxyacetic acid) was observed, whereas at higher concentration, three photoproducts were formed, with 2,4-dichlorophenol as the third one. These photoproducts appeared competitively within about 40–80 min, and were eventually photodecomposed. The experimental data are in good agreement with the results of our HF-DFT calculations

A comparison of the environmental impact of pesticide multiresidues and their occurrence in river waters surveyed by liquid chromatography coupled in tandem with UV diode array detection and mass spectrometry

9 pages, 4 figures, 3 tables.-- PMID: 15051367 [PubMed].-- Printed version published May 2004.Twenty-two pesticides and metabolites selected on the basis of a regional priority list, were surveyed in surface river waters by high performance liquid chromatography coupled in tandem with UV diode array detection and mass spectrometry, after an off-line pre-concentration step. Pesticide concentrations ranged between 0.07 and 4.8 μg/l according to the compound and sampling period. Analytical results were linked to the environmental risk of pesticides, evaluated by their system investigation of risk by integration of score (SIRIS) rank.S. Irace-Guigand gratefully acknowledges the University Pierre and Marie Curie (Paris FRANCE) and the PIREN-Seine project for financial support of her Ph.D., as well as the help and encouragements of Professor Ghislain de Marsily.Peer reviewe

Theoretical and experimental approach for the study of 2,4-dichlorophenoxyacetic acid photodegradation: C-O versus C-Cl bond dissociation energies in the gas phase and aqueous medium

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