Síntese verde, estudo termoanalítico e caracterização de uma base de schiff e seus complexos de Co(II), Cu(II) e Zn(II)
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Data
2021-05-20
Autores
Benedito Júnior, José
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Universidade Estadual Paulista (Unesp)
Resumo
As bases de Schiff, utilizadas em estudos de reações orgânicas, desempenham função de base de Lewis, o que confere a estes compostos uma gama de aplicações. Visando seguir os princípios da Química Verde, necessidade de minimizar a geração de resíduos e a utilização de métodos alternativos com menor impacto ambiental, nesse trabalho utilizou-se o método mecanoquímico na síntese da base de Schiff (H2BS) a partir do fármaco ácido 4-aminosalicílico (4-ASA) com o Salicilaldeído. A partir do ligante foram sintetizados os compostos de coordenação de Co (II), Cu (II) e Zn (II) por precipitação em meio aquoso. A estrutura molecular do ligante H2BS foi elucidada pelas técnicas de RMN unidimensional (RMN 1H e DEPTQ) e bidimensional (HSQC). Também foram utilizadas as técnicas de Espectroscopia Vibracional de Absorção no Infravermelho Transformada de Fourier (FTIR) para caracterização do ligante, sendo que o resultado de FTIR proporcionaram a identificação dos sítios de coordenação do ligante aos íons metálicos. Os complexos de cobre e zinco se coordenam pelo grupo carboxilato e o oxigênio fenolato formando um anel quelato, já o complexo de cobalto coordena-se com o grupo carboxilato por meio de uma ligação iônica ou pode coordenar em modo quelante ou ponte. As propriedades termoanalíticas tanto do ligante quanto dos complexos foram determinadas pelas técnicas de termogravimetria e calorimetria exploratória diferencial simultâneas (TG-DSC) e calorimetria exploratória diferencial (DSC). Com os resultados de TG-DSC foram sugeridas as seguintes formula mínimas para os composto de coordenação: [[Co(SB)(OH2)2]; [Cu(SB)].0,5 H2O, e [Zn (SB)].0,5 H2O . As micrografias e as curvas DSC mostraram o processo de desidratação para todos os complexos, já para o complexo de cobalto a desidratação ocorreu até 130 °C, sugerindo que as moléculas de água estavam coordenadas ao metal. Os resultados de FTIR e UV-Vis/NIR corroboraram para a sugestão da coordenação do íon cobalto com a molécula de água. Por fim, os resultados de difratometria de raios X do pó (DRXP) dos complexos mostraram que a cristalinidade diminui conforme aumenta o número atômico, sendo o complexo de cobalto mais cristalino e o complexo de zinco apresentando um padrão de difração característico de material amorfo.
The Schiff bases, used in studies of organic reactions, perform a basic function of Lewis, which gives these compounds a range of applications. To follow the principles of Green Chemistry, the need to minimize waste generation and the use of alternative methods with less environmental impact, in this paper the mechanochemical method was used in the synthesis of the Schiff base (H2BS) from the drug 4-aminosalicylic acid (4-ASA) with Salicylaldehyde. From the ligand were synthesized the coordination compounds of Co (II), Cu (II), and Zn (II) by precipitation in an aqueous medium. The molecular structure of the H2BS ligand was elucidated by the techniques of one-dimensional NMR (1H NMR and DEPTQ) and two-dimensional (HSQC) techniques. The techniques of Fourier Transformed Infrared Absorption Vibrational Spectroscopy (FTIR) were also used to characterize the ligand, and the FTIR result provided the identification of the sites of coordination of the ligand to the metal ions. The copper and zinc complexes are coordinated by the carboxylate group and the phenolate oxygen forming a chelate ring, while the cobalt complex coordinates with the carboxylate group by means of an ionic bond or can coordinate in a chelating or bridge mode. The thermoanalytical properties of both the ligand and the complexes were determined by simultaneous exploratory calorimetry and calorimetry (TG-DSC) and differential exploratory calorimetry (CSD) techniques. With the results of TG-DSC, the following minimum formulas were suggested for the coordination compounds: [[Co(SB)(OH2)2]; [Cu(SB)].0.5 H2O, and [Zn (SB)].0.5 H2O. Micrographs and DSC curves showed the dehydration process for all complexes, while for the cobalt complex dehydration occurred up to 130 °C, suggesting that the water molecules were coordinated to the metal. The results of FTIR and UVVis/NIR corroborated the suggestion of coordination of cobalt ion with the water molecule. Finally, the results of powder X-ray dilate (DRXP) of the complexes showed that crystallinity decreases as the atomic number increases, with the cobalt complex being more crystalline and the zinc complex presenting a characteristic diffraction pattern of amorphous material.
The Schiff bases, used in studies of organic reactions, perform a basic function of Lewis, which gives these compounds a range of applications. To follow the principles of Green Chemistry, the need to minimize waste generation and the use of alternative methods with less environmental impact, in this paper the mechanochemical method was used in the synthesis of the Schiff base (H2BS) from the drug 4-aminosalicylic acid (4-ASA) with Salicylaldehyde. From the ligand were synthesized the coordination compounds of Co (II), Cu (II), and Zn (II) by precipitation in an aqueous medium. The molecular structure of the H2BS ligand was elucidated by the techniques of one-dimensional NMR (1H NMR and DEPTQ) and two-dimensional (HSQC) techniques. The techniques of Fourier Transformed Infrared Absorption Vibrational Spectroscopy (FTIR) were also used to characterize the ligand, and the FTIR result provided the identification of the sites of coordination of the ligand to the metal ions. The copper and zinc complexes are coordinated by the carboxylate group and the phenolate oxygen forming a chelate ring, while the cobalt complex coordinates with the carboxylate group by means of an ionic bond or can coordinate in a chelating or bridge mode. The thermoanalytical properties of both the ligand and the complexes were determined by simultaneous exploratory calorimetry and calorimetry (TG-DSC) and differential exploratory calorimetry (CSD) techniques. With the results of TG-DSC, the following minimum formulas were suggested for the coordination compounds: [[Co(SB)(OH2)2]; [Cu(SB)].0.5 H2O, and [Zn (SB)].0.5 H2O. Micrographs and DSC curves showed the dehydration process for all complexes, while for the cobalt complex dehydration occurred up to 130 °C, suggesting that the water molecules were coordinated to the metal. The results of FTIR and UVVis/NIR corroborated the suggestion of coordination of cobalt ion with the water molecule. Finally, the results of powder X-ray dilate (DRXP) of the complexes showed that crystallinity decreases as the atomic number increases, with the cobalt complex being more crystalline and the zinc complex presenting a characteristic diffraction pattern of amorphous material.
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Palavras-chave
Base de Schiff, Ácido 4-aminosalicílico, Compostos de coordenação, Mecanoquímica, Análise térmica, Schiff base, 4-aminosalicylic acid, Coordination compounds, Mechanochemica, Thermal analysis