Partículas de óxido de ferro magnéticas modificadas com ácido p-sulfônico-calix[4]areno: preparação e uso em reações multicomponentes e de valoração do glicerol

Abstract

The objective of this work was to synthesize magnetic particles of on iron oxide and modify the surface of this material with the organocatalyst p-sulfonic-calix[4]arene acid. Next, the catalysis of organic reactions promoted by the modified magnetic particles was investigated. The reactions where the particles were used as catalysts were: Biginelli reaction, xanthenone synthesis and synthesis of acetals derived from glycerol, the latter in order to add value to the glycerin. The synthesis of the magnetic particles can be made from different methodologies, in this work, the precipitation method, Pechini and solvothermic, was used. Then, the surface modification of these oxides was carried out by inserting a silica layer and then the p-sulfonic-calix[4]arene acid was covalently bound to the surface of the material, giving rise to the three catalysts that had their activity catalytic evaluation. The materials synthesized presented varied chemical compositions, in addition, they are morphologically distinct, so it was observed that the catalytic activity of these materials was different in the reactions studied. In Biginelli's reaction, the three catalysts were efficient. However, the one in which the magnetic support was synthesized by the precipitation method was the most efficient, leading to the formation of products with up to 88% yield. Similar behavior was observed for the xanthenone reaction. Although the three materials were efficient to promote the reaction catalysis, the catalyst in which the magnetic support was synthesized by the precipitation method led to the formation of xanthenones in up to 87% yield. Finally, in the aldehyde acetalization reaction with glycerol, the catalysis was promoted with higher efficiency by the catalyst in which the magnetic support was synthesized by the precipitation method. Products of up to 93% yield were obtained when the aldehyde employed contained the methoxy group at the para position of the aromatic ring. In addition, aiming for greater selectivity in obtaining acetals of five or six limbs, the variation of the reaction conditions (130° C and 30 min) only led to formation of the six-member isomer. Thus, it is concluded that the catalyst, whose magnetic support was obtained by the precipitation method, was the most efficient in all the reactions studied in this work. Thus, it is promising to study this material as a catalyst in other reactions that require acidic media to process efficiently.