Estudo da atividade catalítica do óxido de grafite em reações orgânicas
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2021-12-14
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Universidade Federal de Goiás
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Graphite oxide (OGt) is characterized as graphite sheets with randomly distributed aromatic regions (sp2 carbon atoms) and oxygenated aliphatic regions (sp3 carbon atoms); has different functional groups such as hydroxyl, epoxy and carboxyl. The presence of these groups confers an acidic character to the material and, due to its biocompatibility, easy reuse, it can be considered a promising heterogeneous catalyst. Thus, we sought to use graphite oxide as an acid catalyst for the following organic reactions: Pechmann, reaction of disubstituted benzimidazoles, Mannich and Biginelli-like. To obtain graphite oxide, the Hummers method was used, in which graphite is oxidized involving a mixture of sodium nitrate, potassium permanganate and concentrated sulfuric acid; however, the methodology is a time-consuming and low-yield process. Thus, the graphite oxide was characterized by X-ray diffraction, IR spectroscopy, thermogravimetic analysis and by electron microscopy, which allowed to evaluate the oxidation process of graphite in graphite oxide. In this study, the reactions were analyzed in many parameters, such as: temperature, stoichiometric ratio, solvents, and amount of catalyst. Thus, when testing graphite oxide in these reactions, it was observed that OGt presented different behavior in each type of reaction; it was found that for the disubstituted benzimidazoles only 30 mg were needed to obtain a yield greater than 80%, while for the Biginelli-like reaction 300 mg was used and a yield below 80% was obtained. However, conditions were sought in which the reactions occurred in the absence of solvent, in order to make the processes environmentally friendly with the use of graphite oxide as a heterogeneous solid catalyst. Furthermore, the variation of substrates was evaluated for all reactions, which allowed us to observe that the best yields occurred with substrates in the presence of electron activating groups, while for the Pechmann, Mannich and Biginelli-like reactions there was no formation of products with an electron-withdrawing group -NO2. All products were characterized by 1H and 13C NMR and were identified by comparison with the spectra reported in the literature.
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NAVES, Raquel Ferreira. Estudo da atividade catalítica do óxido de grafite em reações orgânicas. 2021. 238 f. Tese (Doutorado em Química). Universidade Federal de Goiás, Goiânia, 2021.