Calix[n]arenos como organocatalisadores para reações de esterificação

• Autor(a) principal: Natalino, Ricardo
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/222
• topic: Calix[n]arenos; Organocatalisadores; Esterificação; RMN DE 1H; Calix[n]arenes; Organocatalysts; Esterification; 1H NMR; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA

This thesis aimed to develop organocatalysers inspired by calix[n]arenes for esterification reactions of organic acids. First the conversion of the esterification reactions of deuterated palmitic acid with methanol by 1H NMR and subestechiometrics with stoichiometric amounts (0.5 mol%) of two organocatalysers (p-sulfonic acid calix[4]arene and p-sulfonic acid calix[6]arene) and two commercial catalysts (sulfuric acid and p-toluene sulfonic acid) were determined. From this information, the kinetic and thermodynamic parameters for the esterification reactions were calculated. The sulfuric acid catalyst in stoichiometric quantities was abandoned due to rapid and high conversion rate of palmitic acid ester. The catalyst ptoluene sulfonic acid showed no catalytic activity when used in appreciable substoichiometric quantities not being determined any kinetic and hermodynamic parameters for the same. The catalytic activity and conversion of palmitic acid ester with the other three catalysts were similar. All kinetic and thermodynamic parameters determined demonstrate that sulfuric acid shows the best parameters followed by p-sulfonic acid calix[6]arene and finally the p-sulfonic acid calix[4]arene for the esterification of palmitic acid. In order to test the efficiency of two organocatalysers and compare them with two commercial catalysts employed in the same reactions of esterification of 16 organic acids, we observed that the catalysts showed conversions to fatty esters using similar substoichiometric amounts of catalyst (0.5 mol%), reaching up to 99% conversion in some cases. By employing the catalyst p-toluene sulfonic acid (0.5 mol%) the best conversion to palmitic acid ester was only 42%. We also noticed that the optimum concentration of the catalysts (sulfuric acid, p-sulfonic acid calix[4]arene and psulfonic acid calix[6]arene) at 50 °C for the esterification reactions is 2.5 mol% with no significant changes when we doubled the catalyst concentration (5.0 mol%). The 1H NMR technique used to obtain kinetic and thermodynamic parameters organic acids for reactions of esterification proved to be a very effective tool. Finally we demonstrate the efficiency of both new organocatalysers based on calix[n]arenes for esterification reactions to a series of 16 organic acids with the great advantage of being recovered at the end of the reaction and reused without losing its catalytic activity.