Mechanism of hydroxyl radical-induced breakdown of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-d).
Oxidative transformations by the hydroxyl radical are significant in advanced oxidation processes for the breakdown of organic pollutants, yet mechanistic details of the reactions are lacking. A combination of experimental and computational methods has been employed in this study to elucidate the reactivity of the hydroxyl radical with the widely used herbicide 2,4-D (2,4-dichlorophenoxyacetic acid). The experimental data on the reactivity of the hydroxyl radical in the degradation of the herbicide 2,4-D were obtained from gamma-radiolysis experiments with both (18)O-labeled and unlabeled water. These were complemented by computational studies of the (.)OH attack on 2,4-D and 2,4-DCP (2,4-dichlorophenol) in the gas phase and in solution. These studies firmly established the kinetically controlled attack ipso to the ether functionality as the main reaction pathway of (.)OH and 2,4-D, followed by homolytic elimination of the ether side chain. In addition, the majority of the early intermediates in the reaction between the hydroxyl radical and 2,4-DCP, the major intermediate, were identified experimentally. While the hydroxyl radical attacks 2,4-D by (.)OH-addition/elimination on the aromatic ring, the oxidative breakdown of 2,4-DCP occurs through (.)OH addition followed by either elimination of chlorine or formation of the ensuing dichlorophenoxyl radical.
Peller
Julie
J
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556-5670, USA.
Wiest
Olaf
O
Kamat
Prashant V
PV
D015084:2,4-Dichlorophenoxyacetic Acid / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D006540:Herbicides / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry*; D008958:Models, Molecular; D016877:Oxidants / Q000737:chemistry*; D010084:Oxidation-Reduction; D013997:Time Factors
D006540:Herbicides; D016877:Oxidants; D015084:2,4-Dichlorophenoxyacetic Acid; D017665:Hydroxyl Radical