Propazine (2-chloro-4,6-diisopropylamino-1,3,5-triazine) is a triazine herbicide used to control broadleaf weeds and annual grasses during the production of milo grain sorghum. This compound provides post-emergent protection by interfering with photosynthetic electron transport of target weeds. Tolerant crops are able to degrade the applied herbicide to nontoxic metabolites. Propazine is electrochemically active under acidic conditions. Electrochemical reduction pathways for this herbicide have been proposed based on differential pulse polarography (DPP) studies. Theoretical deconvolutions of the experimental polarograms were consistent with a 2-electron cleavage of the C-Cl bond via a mechanism involving a protonation step in between the two electron transfers. The resulting intermediate was then reduced by an irreversible 2-electron reduction of the ring to produce the final product. We report supporting nuclear magnetic resonance (NMR) evidence for the electrochemical dechlorination of propazine and reduction of the triazine ring using controlled potential electrolysis (CPE) and a mercury pool electrode under acidic conditions.
Bibliographical noteFunding Information:
The authors would like to thank the Minnesota Center for Teaching and Learning (CTL) for the grant to purchase the BioAnalytical Systems Epsilon-2 potentiostat. The Waters Breeze HPLC was purchased using Minnesota Higher Education Preservation and Renewal (HEPR) funds. The Varian Gemini-2000 NMR spectrometer was purchased with a grant from the National Science Foundation (NSF) in addition to matching funds from Southwest Minnesota State University (SMSU). We would also like to thank the National Institute of Advanced Industrial Science and Technology (AIST; Japan) for access to their spectral database. We appreciate the herbicide samples purchased with financial support from the SMSU Foundation. The group would also like to thank the SMSU Environmental Science Program for the use of their laboratory space during our preparation of hydroxypropazine. Finally, J.H.B. is grateful for the funds provided by the SMSU Faculty Improvement Grant (FIG) committee to purchase select components of the in-house constructed bulk electrolysis cell.
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