Aqueous Oxidation of Phenylurea Herbicides by Triplet Aromatic Ketones
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- 作者：Silvio Canonica ; BrunoHellrung ; Pavel Mü ; ller ; Jakob Wirz
- 刊名：Environmental Science & Technology
- 出版年：2006
- 出版时间：November 1, 2006
- 年：2006
- 卷：40
- 期：21
- 页码：6636 - 6641
- 全文大小：753K
- 年卷期：v.40,no.21(November 1, 2006)
- ISSN：1520-5851
文摘
Excited triplet states of dissolved natural organic matter(DOM) are important players for the transformation of organicchemical contaminants in sunlit natural waters. Thepresent study focuses on kinetics and mechanistic aspectsof the transformation of phenylurea herbicides inducedby well-defined excited triplet states, which have beenchosen to model DOM triplet states having oxidative character.The aromatic ketones benzophenone, 3'-methoxy-acetophenone, and 2-acetonaphthone were used tophotogenerate their triplet states and oxidize a series ofeleven substituted phenylureas. Quenching of the excitedtriplet states by the phenylureas was measured usinglaser flash photolysis in the microsecond time domain, whilethe oxidation kinetics of the phenylureas was followedunder steady-state irradiation. Second-order rate constantsfor quenching and oxidation were largely identical for agiven pair of ketone and phenylurea. They reachedthe diffusion-controlled limit (
4 × 109 M-1 s-1) anddecreased with increasing free energy of electron transferfrom the phenylurea to the ketone triplet. These resultsconfirm those already obtained using phenols as the substratesto be oxidized and suggest that oxidation rates aremainly determined by the bimolecular rate constant forelectron transfer, a rule that can possibly be extended tovarious organic contaminants. A refined estimate of theeffective reduction potential of DOM excited triplet stateswas also obtained.
4 × 109 M-1 s-1) anddecreased with increasing free energy of electron transferfrom the phenylurea to the ketone triplet. These resultsconfirm those already obtained using phenols as the substratesto be oxidized and suggest that oxidation rates aremainly determined by the bimolecular rate constant forelectron transfer, a rule that can possibly be extended tovarious organic contaminants. A refined estimate of theeffective reduction potential of DOM excited triplet stateswas also obtained.