Theoretical investigation of the OH-initiated atmospheric decomposition of chlorpyrifos and chlorpyrifos-methyl

• Ano de defesa: 2020
• Autor(a) principal: Mateus Macedo Quintano
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Minas Gerais; Brasil; ICX - DEPARTAMENTO DE QUÍMICA; Programa de Pós-Graduação em Química; UFMG
• Palavras-chave em Português: Chlorpyrifos; Chlorpyrifos-methyl; Atmospheric decomposition mechanism; Density functional theory (DFT); Dispersion corrections; Transition state theory (TST); FOD analysis tool; Clorpirifós; Metil-clorpirifós; Mecanismo de decomposição atmosférica; Teoria do funcional de densidade (DFT); Correções dispersivas; Teoria do estado de transição (TST); Análise FOD; Físico-química; Atmosfera – Pesticidas – Decomposição química; Pesticidas – Aspectos ambientais; Funcionais de densidade; Compostos organofosforados
• Link de acesso: http://hdl.handle.net/1843/36105

This work aimed for an elucidation of the mechanism of tropospheric decomposition of the organophosphorus pesticides chlorpyrifos and chlorpyrifos-methyl using calculations based on the density functional theory (DFT) with dispersion correction and on the transition state theory (TST). We proposed a novel alternative route for the unimolecular decomposition of OH-initiated intermediates produced by OH-addition to the thiophosphoryl bond. Within such route, 3,5,6-trichloro-2-pyridinol (TCP), which is one of the main carbon-containing breakdown products, is obtained in a single step. Besides, we showed that TCP exists according to a ketone-enol equilibrium in the atmosphere at the ambient conditions. Also, we were able to show that the OH-addition occurs preferentially at the phosphorus atom. The P-bonded adducts can either follow a unimolecular decomposition pathway or react competitively with molecular oxygen, which accounts for the formation of the corresponding oxone.