Reação de Claisen-Schmidt catalisada por carvões ativados de origem vegetal
Nenhuma Miniatura disponível
Data
2020-03-27
Autores
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Federal de Goiás
Resumo
Claisen-Schmidt reaction allows chalcones synthesis, which present biological activity of great interest, as anticancer, by acid or basic catalysis. Activated carbons were prepared with vegetable biomass from domestic or industrial waste, as pequi external mesocarp and shells, coffee grounds and malt bagasse by dehydration with sulfuric acid (98%), washed with distilled water until pH 4 and dried. A portion of prepared carbons were subjected to an alkaline treatment with NaOH 2 mol/L solution and washed with distilled water to pH 8 and dried. Additionally, activated carbons from babassu powdered and granulated, obtained by the industrial process of physical activation, were submitted to the same alkaline treatment. Carbons were characterized by scanning electron microscopy (SEM), thermogravimetry (TG), differential thermal analysis (DTA), textural analysis, infrared spectroscopy (FT-IR), X-rays diffraction (XRD), CHNS elemental analysis and determination of acid and basic sites by the Boehm method. The prepared carbons were tested as catalysts on Claisen-Schmidt condensation reaction between Acetophenone and 4-nitrobenzaldehyde using methanol as solvent at room temperature for 24 h. The conversion of acetophenone was evaluated on HPLC. The highest conversion among carbons produced by dehydration was obtained for coffee grounds carbon with basic characteristics, 64.19%. Among carbons with acid characteristics, the best conversion was 61.70%, for carbon obtained from pequi shell. The reuse test of the activated carbon from pequi shell with acidic characteristics for the reaction under study provided a conversion of 46.50%. Among the industrial carbons, the best was the granulated, achieving conversion of 69.26%. The kinetic study of Claisen-Schmidt reaction was carried out with treated industrial granular carbon, as it showed a higher conversion than the pulverized one and less operational difficulties in a continuous reactor. The reaction kinetics of second global order and the rate constants were determined at 35°C and 50°C. The activation energy calculated for this reaction was 18.91 kJ/mol. The conversion in a fixed bed continuous reactor for 1:1 molar ratio of reactants, with acetophenone and 4-nitrobenzaldehyde initial concentration of 0.05 mol/L, achieved 60.23% in 10 min with ascending flow, for a period of 90 min. Another reaction of aldol condensation was evaluated with NaOH-treated granulated babassu catalyst to obtain (1E,4E)-1-(4-nitrophenyl)-5-(2,6,6-trimethyl-1-ciclohexen-1-yl)-1,4-pentadien-3-one. The reaction was conducted between 3 mmol of β-ionone and 2.5 mmol of 4-nitrobenzaldehyde at 27°C and 55°C. After only 1 h of reaction at 55°C the conversion achieved over 4-nitrobenzaldehyde was 63.95%, while at 27°C it was 28.87%. The specific speed constants and activation energy obtained for the reaction demonstrated the production of this compound is strongly affected by temperature. After 4.5 h of reaction the yield achieved was 82%, indicating a great potential for activated carbons from vegetable source in heterogeneous catalysis.
Descrição
Palavras-chave
Citação
WINTER, C. Reação de Claisen-Schmidt catalisada por carvões ativados de origem vegetal. 2020. 128 f. Tese (Doutorado em Química) - Universidade Federal de Goiás, Goiânia, 2020.