Photodegradation of the herbicide penoxsulam in aqueous methanol and acetonitrile

Abstract

Penoxsulam is a triazolopyrimidine sulfonamide group of rice herbicide. The phototransformation of penoxsulam was studied under UV light (λ_max ≥ 290 nm) and sunlight in aqueous methanol and acetonitrile solvent system using TiO₂ as sensitizer. The rate of photodegradation of penoxsulam in different solvent systems followed first-order kinetics and calculated half-lives was found to be in the range of 51.89–73.41 h and 62.70–97.09 h for UV light and sunlight respectively in the presence or absence of sensitizer. From this study, a total of six photoproducts were identified and characterized on the basis of Q-Tof micromass spectral data. The plausible mechanism of phototransformation involved were hydrolysis, photo oxidation of the sulfonamide group, breaking of sulfonamide bond, loss of amino and sulfonic acid group.

Keywords:

• Penoxsulam
• photoproduct
• methanol
• acetonitrile
• UV light
• sunlight

Acknowledgments

We thank M/s Dow AgroSciences India Pvt. Ltd., Mumbai, India for supplying analytical standard of penoxsulam. We are grateful to IICB, Kolkata, for Q-Tof micromass spectral analysis and to Bidhan Chandra Krishi Viswavidyalaya (BCKV) for infrastructural facilities. We are thankful to Mr. Sukdeb Pal, Seoul National University, Korea, for his kind cooperation in respect of some review collection.

Notes

*The relative amount of each compound was calculated by using the relative amounts of each compound present in the extract obtained from each solvent system, which was obtained in the Q-Tof micromass spectra.