Abstract
In this study, the degradation mechanism of chloroacetanilide herbicides in the presence of four different nucleophiles, namely: Br−, I−, HS−, and S2O3−2, was theoretically evaluated using the dispersion-corrected hybrid functional wB97XD and the DGDZVP as a basis set. The comparison of computed activation energies with experimental data shows an excellent correlation (R2 = 0.98 for alachlor and 0.97 for propachlor). The results suggest that the best nucleophiles are those where a sulfur atom performs the nucleophilic attack, whereas the other species are less reactive. Furthermore, it was observed that the different R groups of chloroacetanilide herbicides have a negligible effect on the activation energy of the process. Further insights into the mechanism show that geometrical changes and electronic rearrangements contribute 60% and 40% of the activation energy, respectively. A deeper analysis of the reaction coordinate was conducted, employing the evolution chemical potential, hardness, and electrophilicity index, as well as the electronic flux. The charge analysis shows that the electron density of chlorine increases as the nucleophilic attack occurs. Finally, NBO analysis indicates that the nucleophilic substitution in chloroacetanilides is an asynchronous process with a late transition state for all models except for the case of the iodide attack, which occurs through an early transition state in the reaction.
Highlights
The presence of weeds and grasses competing with plants for resources such as nutrients, water and sunlight has become a serious agricultural problem that hampers high yields in crops [1]
Following ofeach eachchloroacetanilide chloroacetanilide with the four different nucleophiles was studied and their activation free energies calculated
It is known that nucleophiles was studied and their activation free energies calculated
Summary
The presence of weeds and grasses competing with plants for resources such as nutrients, water and sunlight has become a serious agricultural problem that hampers high yields in crops [1]. Chloroacetanilides, first synthesized in the 1960s, represent a family of herbicides that includes products such as: metolachlor, acetochlor, butachlor, and alachlor This family of compounds represents one of the most widely used pesticides worldwide to fight small-seeded broadleaf weeds and annual grasses [4,5]. The use of these compounds, and their production, has significantly increased since 1980. The particular case of acetochlor, metolachlor, and alachlor reach the 4th (~33 million lb), 10th (~18 million lb), and 16th (~8 million lb) place in the most widely used agricultural chemicals in the US, according to the United States Environmental Protection Agency (US EPA) [7,8] Their use has been observed to reach countries in Africa, Europe, Latin America [3,9]. China is a great consumer of chloroacetanilide herbicides, using around 10,000 metric tons every year [4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
