Kinetics, mechanism, and tautomerism in ametryn acid hydrolysis: From molecular structure to environmental impacts

Bruno Ramos; Wesley F Vaz; Luan F Diniz; Flavio O Sanches Neto; Julio C O Ribeiro; Valter H Carvalho-Silva; Antonio Carlos S C Teixeira; Caue Ribeiro; Hamilton B Napolitano; Paulo S Carvalho Jr

doi:10.1016/j.chemosphere.2023.138278

Kinetics, mechanism, and tautomerism in ametryn acid hydrolysis: From molecular structure to environmental impacts

Chemosphere. 2023 May:324:138278. doi: 10.1016/j.chemosphere.2023.138278. Epub 2023 Mar 4.

Affiliations

¹ Research Group in Advanced Oxidation Processes (AdOx), Department of Chemical Engineering, Escola Politécica, University of São Paulo, São Paulo, 05088000, Brazil. Electronic address: bruno.ramos@usp.br.
² Theoretical and Structural Chemistry Group, Goiás State University, 75132-903, Anápolis, Brazil.
³ Medicine and Cosmetic Quality Control Laboratory, Pharmaceutical Products Department, Pharmacy Faculty, Federal University of Minas Gerais, 31270-901, Belo Horizonte, Brazil.
⁴ Institute of Chemistry, University of Brasília, Postal Box 4478, 70904-970, Brasília, Brazil; Laboratory for Modeling of Physical and Chemical Transformations, Theoretical and Structural Chemistry Group, Goiás State University, 75132-903, Anápolis, Brazil.
⁵ Laboratory for Modeling of Physical and Chemical Transformations, Theoretical and Structural Chemistry Group, Goiás State University, 75132-903, Anápolis, Brazil.
⁶ Institute of Chemistry, University of Brasília, Postal Box 4478, 70904-970, Brasília, Brazil; Laboratory for Modeling of Physical and Chemical Transformations, Theoretical and Structural Chemistry Group, Goiás State University, 75132-903, Anápolis, Brazil. Electronic address: fatioleg@gmail.com.
⁷ Research Group in Advanced Oxidation Processes (AdOx), Department of Chemical Engineering, Escola Politécica, University of São Paulo, São Paulo, 05088000, Brazil. Electronic address: acscteix@usp.br.
⁸ National Nanotechnology Laboratory for Agribusiness (LNNA), EMBRAPA Instrumentation, 13560-970, São Carlos, SP, Brazil.
⁹ Physics Institute, Federal University of Mato Grosso do Sul, 79074-460, Campo Grande, MS, Brazil. Electronic address: paulo.sousa@ufms.br.

PMID: 36878364
DOI: 10.1016/j.chemosphere.2023.138278

Abstract

The excessive use of pesticides and the demand for environmentally friendly compounds have driven the focus to detailed studies of the environmental destination of these compounds. Degradation by hydrolysis of pesticides, when released into the soil, can result in the formation of metabolites with potentially adverse effects on the environment. Moving in this direction, we investigated the mechanism of acid hydrolysis of the herbicide ametryn (AMT) and predicted the toxicities of metabolites through experimental and theoretical approaches. The formation of ionized hydroxyatrazine (HA) occurs with the release of the SCH₃- group and the addition of H₃O⁺ to the triazine ring. The tautomerization reactions privileged the conversion of AMT into HA. Furthermore, the ionized HA is stabilized by an intramolecular reaction that provides the molecule in two tautomeric states. Experimentally, the hydrolysis of AMT was obtained under acidic conditions and at room temperature with HA as the main product. HA was isolated in a solid state through its crystallization as organic counterions. The mechanism of conversion of AMT to HA and the experimental investigation of the reaction kinetics allowed us to determine the dissociation of CH₃SH as the rate-controlling step in the degradation process that culminates in a half-life between 7 and 24 months under typical acid soil conditions of the Brazilian Midwest - region with strong agricultural and livestock vocation. The keto and hydroxy metabolites showed substantial thermodynamic stability and a decrease in toxicity compared to AMT. We hope that this comprehensive study will support the understanding of the degradation of s-triazine-based pesticides.

Keywords: Acid hydrolysis; Ametryn; DFT; Doehlert matrix; Triazines.

MeSH terms

Herbicides* / toxicity
Hydrolysis
Kinetics
Molecular Structure
Soil
Triazines* / chemistry

Substances

ametryne
Triazines
Herbicides
Soil