Desenvolvimento de uma sílica porosa funcionalizada com grupos carboxilatos e Ce(III) para a catálise da hidrólise de fosfodiésteres

Abstract

Phosphate esters are among the most stable compounds found in nature regard hydrolytic reactions. Metallic ions, in special lanthanide ions, are very good catalysts for such reactions. However, lanthanide ions tendency to precipitate in neutral to slightly basic media requiresthe development of ligands to stabilize them maintaining their activity. In this work, porous silica materials were used in as supports for dispersion of homogeneous catalysts, allowing their recover and reuse. A porous silica was synthesized in basic medium in the presence ofcetyltrimethylammonium bromide and tetraethyl orthosilicate, functionalized with propylnitrile groups, which were hydrolyzed to carboxylic acids in strongly acidic medium under heat. Thismaterial was coordinatedwith Ce3+ ions by different methods. The materials were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry analysis, elemental analysis, X-ray fluorescence, scanning electron microscopy, transmission electron microscopy zeta potential and dynamic light scattering. Their catalytic activities were evaluated for the hydrolysis of bis(2,4-dinitrophenyl)phosphatein different pH at 25 °C. Thematerials coordinated with Ce3+ were active, catalyzing the reaction up to 27-fold. The materials showed optimum catalysis above pH 6.5. This behavior suggested that a hydroxide ion coordinated to Ce3+ was the nucleophile in the hydrolysis of the substrate. The kinetic profile of the materials showed an increase in the in the reaction rate in its course. The reuse after drying of the catalyst showed twice the rate of its first use, showing the same kinetic profile with an induction period. The reuse without previous drying showed an increase in the reaction rate up to about 320-fold, with a first order kinetic profile. These results indicatedthat the catalytic activity of the material was best after an induction period that depended of hydration of the material.