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

Author(s)

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

• Document type: Journal article
• Source: Chemosphere; v. 324, p. 10-pg., 2023-03-10.

Abstract

The excessive use of pesticides and the demand for environmentally friendly compounds have driven the focus 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 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, 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 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 determine the dissociation of CH3SH as the rate-controlling step in the degradation process that culminates in 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. (AU)

• FAPESP's process: 19/24158-9 - Environmental fate of emerging pollutants in surface waters and sustainable alternatives for their mitigation: a hybrid experimental & theoretical approach
• Grantee: Antonio Carlos Silva Costa Teixeira
• Support Opportunities: Regular Research Grants