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Title: Photolysis of natural B-triketonic herbicides in water

Author
item TRIVELLA, AURELIEN - National Council For Scientific Research-Cnrs
item STAWINOGA, MALGORZATA - National Council For Scientific Research-Cnrs
item Dayan, Franck
item Cantrell, Charles
item MAZELLIER, PATRICK - University Of Bordeaux
item RICHARD, CLAIRE - National Council For Scientific Research-Cnrs

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2015
Publication Date: 4/9/2015
Publication URL: http://handle.nal.usda.gov/10113/62275
Citation: Trivella, A., Stawinoga, M., Dayan, F.E., Cantrell, C.L., Mazellier, P., Richard, C. 2015. Photolysis of natural B-triketonic herbicides in water. Water Research. 78:28-36.

Interpretive Summary: Unlike most essential oils that are used to as contact burn-down herbicides, manuka oil has good premergence systemic activity. Since its components are structurally similar to certain commercial herbicides, its photostability was investigated to better understand their potential use as a herbicides. The compounds oxidize faster in the presence of light than in darkness, with leptospermone and grandiflorone being the most photolabile compounds. Photooxidation occurs primarily on the carbon atom bearing the acidic hydrogen atom. The degradation products are charaterized.

Technical Abstract: The fate of four natural triketones (leptospermone, isoleptospermone, grandiflorone and flavesone, pKa=4.0 to 4.5) in aqueous solution, in the dark and upon simulated solar light irradiation was investigated. In anionic form, triketones undergo oxidation in the dark, however, photolysis is much faster than dark reaction. Polychromatic quantum yields vary from 1.2×10-4 to 3.7×10-4, leptospermone and grandiflorone being the most photolabile compounds. Triketones are photooxidized and oxidation dominantly takes place on the carbon atom bearing the acidic hydrogen atom. In molecular form, volatilization is the main dark process. Photolysis is again the major degradation pathway for leptospermone and grandiflorone. Polychromatic quantum yields lay between 1×10-3 and 2×10-3. They are 8 to 16-fold higher for the molecular than for the anionic forms, but light absorption being significantly lower for molecules than for their anionic counterparts, the rates of photolysis are finally similar for the two forms. Molecular isoleptospermone, grandiflorone and flavesone undergo photooxidation essentially. Interestingly, molecular leptospermone mainly undergoes photoisomerization. This photoreactivity is discussed.