Estudo da interação entre o fungicida thiram e íons ferro (III)
Data
2022-11-23
Autores
Pracchia, Maria Luisa 
Orientadores
Akamatu, Eliana Maíra Agostini Valle
Tipo
Trabalho de conclusão de curso
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Os agrotóxicos são compostos orgânicos amplamente utilizados desde a década de 60 para conter a proliferação de pragas e propiciar o crescimento das culturas agrícolas. O amplo uso desses compostos no Brasil traz à tona questões sobre seu comportamento no ambiente. Os ditiocarbamatos são um grupo de fungicidas amplamente utilizados no Brasil, devido aos seus altos índices de eficiência e baixo custo, esse grupo apresenta em sua composição átomos de enxofre capazes de atuar como ligantes frente a íons metálicos. O thiram é um dos cinco fungicidas da família dos ditiocarbamatos permitidos para uso nas lavouras brasileiras. Dentre os metais passíveis de atuar como centros metálicos em compostos de coordenação está o ferro, muito disponível em território brasileiro. Nesse trabalho avaliou-se interação entre o íon metálico ferro (III) e o fungicida thiram em duas soluções de pH distintos, ácido e neutro, por meio da espectroscopia de UV-Vis e voltametria cíclica. Um planejamento experimental fatorial foi utilizado para a otimização dos experimentos, os fatores escolhidos foram pH e proporção metal ligante, em dois níveis: um alto e um baixo. Foi possível observar no espectro de UV-Vis a presença de duas bandas do thiram, contidas em 215 nm e 270 nm em meio aquoso e 212 nm e 270 nm em meio ácido. As absortividades molares da banda em 270nm do thiram diminuíram de 19151,67 L cm-1. mol-1 na solução de pH neutro para 6843,59 L cm-1 . mol-1 na solução de pH ácido estudada. A presença do metal causou um efeito hipercrômico nas bandas do thiram em ambos os valores de pH sendo o efeito mais intenso na solução de pH ácido. Não foi observado o surgimento de novas bandas com as adições de ferro. Nas análises de voltametria cíclica do íon ferro na solução de pH neutro foi possível observar o pico redução em -0,04 V e as adições de thiram resultaram em deslocamentos do potencial de pico para -0,03V e -0,01 V. Na solução de pH ácido o pico de redução do metal foi observado –0,3V, as adições de thiram resultaram em deslocamentos para -0,33V e –0,34V. As superfícies de resposta foram obtidas para ambas as análises. Para as análises espectroscópicas a absorbância da banda do thiram após as adições de ferro foi adotada como resposta e para as análises eletroquímicas adotou-se como resposta a variação no potencial da redução do metal com a adição do fungicida. O modelo matemático que melhor se adequou a ambas as superfícies foi o 2-way-interaction, o gráfico de pareto demonstrou que o fator proporção altera significativamente ambas as respostas e pH não é um fator significante para a resposta eletroquímica. Após a síntese os espectros de infravermelho e Raman demonstraram que não houve a formação de ligações entre o thiram e o íon Fe (III) uma vez que não foram observadas diferenças significativas entre os espectros dos reagentes e do produto obtido pela síntese.
Pesticides are organic compounds, widely used since the 1960s to contain the proliferation of pests and to promote the growth of agricultural crops. The wide use of these compounds in Brazil raises questions about their behavior in nature. Dithiocarbamates are a group of fungicides widely used in Brazil due to their high efficiency and low cost, this group has sulfur atoms in his composition capable of acting as ligands with metal ions. Thiram is one of five fungicides from the family of dithiocarbamates allowed for use in Brazilian crops. The iron is among the metals that can act as a metallic center in a coordination compound, which is very available in Brazilian territory. In this research, the interaction between the iron (III) metallic ion and the thiram fungicide at two pH's (acid and neutral) was evaluated with a UV-Vis spectroscopy and Cyclic Voltammetry. A factorial experimental design was used to optimize the experiments, the factors chosen were pH and metal-binder ratio, at two levels: a high and a low. It was possible to observe in the UV-Vis spectrum the presence of Thiram in two bands, present on aqueous solution in 215nm and 270nm and 212nm and 270nm in acid solution. The molar absortivities of the band present in 270nm of thiram decreased from 19151.67 L cm-1. mol-1 in neutral pH to 6843.59 L cm-1. mol-1 on acid pH studied. The presence of the metal caused a hyperchromic effect on the thiram bands at both pH, the effect being more intense at acidic pH. It was not observed the appearance of new bands with the addition of iron. In the cyclic voltammetry analysis of iron ion at neutral pH, it was possible to observe the peak reduction at -0.04 V and the additions of thiram resulted in peak potential change to -0.03V and -0.01 V. At acidic pH the peak metal reduction was observed –0.3V, thiram additions resulted in shifts to -0.33V and –0.34V. The response surfaces were obtained for both analyses. For the spectroscopic analysis,the response was the absorbance of the thiram band after the addition of iron and for the electrochemical analysis, the variation in the metal reduction potential with the addition of the fungicide was adopted. The mathematical model that fits better in both surfaces was the 2-way-interaction. The Pareto graph demonstrated that the proportion of the factor significantly alters both responses and pH is not a significant factor for the electrochemical response. After the synthesis, the infrared and Raman spectra showed no formation of bonds between thiram and the Fe(III) ion since no significant differences were observed between the spectra of the reactants and the product obtained by the synthesis.
Pesticides are organic compounds, widely used since the 1960s to contain the proliferation of pests and to promote the growth of agricultural crops. The wide use of these compounds in Brazil raises questions about their behavior in nature. Dithiocarbamates are a group of fungicides widely used in Brazil due to their high efficiency and low cost, this group has sulfur atoms in his composition capable of acting as ligands with metal ions. Thiram is one of five fungicides from the family of dithiocarbamates allowed for use in Brazilian crops. The iron is among the metals that can act as a metallic center in a coordination compound, which is very available in Brazilian territory. In this research, the interaction between the iron (III) metallic ion and the thiram fungicide at two pH's (acid and neutral) was evaluated with a UV-Vis spectroscopy and Cyclic Voltammetry. A factorial experimental design was used to optimize the experiments, the factors chosen were pH and metal-binder ratio, at two levels: a high and a low. It was possible to observe in the UV-Vis spectrum the presence of Thiram in two bands, present on aqueous solution in 215nm and 270nm and 212nm and 270nm in acid solution. The molar absortivities of the band present in 270nm of thiram decreased from 19151.67 L cm-1. mol-1 in neutral pH to 6843.59 L cm-1. mol-1 on acid pH studied. The presence of the metal caused a hyperchromic effect on the thiram bands at both pH, the effect being more intense at acidic pH. It was not observed the appearance of new bands with the addition of iron. In the cyclic voltammetry analysis of iron ion at neutral pH, it was possible to observe the peak reduction at -0.04 V and the additions of thiram resulted in peak potential change to -0.03V and -0.01 V. At acidic pH the peak metal reduction was observed –0.3V, thiram additions resulted in shifts to -0.33V and –0.34V. The response surfaces were obtained for both analyses. For the spectroscopic analysis,the response was the absorbance of the thiram band after the addition of iron and for the electrochemical analysis, the variation in the metal reduction potential with the addition of the fungicide was adopted. The mathematical model that fits better in both surfaces was the 2-way-interaction. The Pareto graph demonstrated that the proportion of the factor significantly alters both responses and pH is not a significant factor for the electrochemical response. After the synthesis, the infrared and Raman spectra showed no formation of bonds between thiram and the Fe(III) ion since no significant differences were observed between the spectra of the reactants and the product obtained by the synthesis.