Síntesis de compuestos heterocíclicos mediante reacción multicomponente catalizada por un heteropoliácido confinado en microesferas de sílice mesoporosa

Como objetivo general de este trabajo se estudiarán heteropolioxometalatos con estructura Keggin confinados en microesferas mesoporosas de sílice, obtenidas a partir del método sol-gel, como catalizadores en reacciones multicomponente de síntesis de compuestos heterocíclicos con potencial actividad biológica. Se propone, así, reemplazar los catalizadores líquidos convencionales por los heteropolioxometalatos, así como usar catalizadores soportados por su fácil recuperación, llevar a cabo las reacciones en ausencia de solvente, como principales variantes. Esto debe permitir obtener compuestos pertenecientes a la familia de los imidazoles tri y tetra sustituidos, a través de reacciones multicomponente.Facultad de Ciencias Exacta

Synthesis of polystyrene microspheres to be used as template in the preparation of hollow spherical materials: study of the operative variables

Mono-disperse polystyrene (PS) spheres were synthesized. The styrene polymerization was carried out using 4,4´-azobis 4-cyanovaleric acid (ACVA) or potassium persulfate (KPS) as initiators in the presence of polyvinyl pyrrolidone (PVP) as surfactant or stabilizing agent. Size measurement and its distribution were followed by scanning electron microscopy. A very narrow size distribution was obtained by controlling the synthesis temperature. For both initiators, it was observed that smaller PS particles are obtained when PVP amount increases. Besides, the ssphere size decreased when KPS amount increased at a fixed PVP concentration. Similar results were obtained for the polystyrene spheres synthesized using ACVA as initiator. On the other hand, the influence of a co-monomer addition in the sphere size was also analyzed. The suitable selection of the initiator type and its concentration, as well as the surfactant agent amount, led to a controlled obtainment of the polystyrene microspheres, appropriate to be used as template in the synthesis of hollow spherical materials.Centro de Investigación y Desarrollo en Ciencias Aplicada

Synthesis of polystyrene microspheres to be used as template in the preparation of hollow spherical materials: study of the operative variables

Mono-disperse polystyrene (PS) spheres were synthesized. The styrene polymerization was carried out using 4,4´-azobis 4-cyanovaleric acid (ACVA) or potassium persulfate (KPS) as initiators in the presence of polyvinyl pyrrolidone (PVP) as surfactant or stabilizing agent. Size measurement and its distribution were followed by scanning electron microscopy. A very narrow size distribution was obtained by controlling the synthesis temperature. For both initiators, it was observed that smaller PS particles are obtained when PVP amount increases. Besides, the ssphere size decreased when KPS amount increased at a fixed PVP concentration. Similar results were obtained for the polystyrene spheres synthesized using ACVA as initiator. On the other hand, the influence of a co-monomer addition in the sphere size was also analyzed. The suitable selection of the initiator type and its concentration, as well as the surfactant agent amount, led to a controlled obtainment of the polystyrene microspheres, appropriate to be used as template in the synthesis of hollow spherical materials.Centro de Investigación y Desarrollo en Ciencias Aplicada

Synthesis of Polystyrene Microspheres to be Used as Template in the Preparation of Hollow Spherical Materials: Study of the Operative Variables

Mono-disperse polystyrene (PS) spheres were synthesized. The styrene polymerization was carried out using 4,4´-azobis 4-cyanovaleric acid (ACVA) or potassium persulfate (KPS) as initiators in the presence of polyvinyl pyrrolidone (PVP) as surfactant or stabilizing agent. Size measurement and its distribution were followed by scanning electron microscopy. A very narrow size distribution was obtained by controlling the synthesis temperature. For both initiators, it was observed that smaller PS particles are obtained when PVP amount increases. Besides, the ssphere size decreased when KPS amount increased at a fixed PVP concentration. Similar results were obtained for the polystyrene spheres synthesized using ACVA as initiator. On the other hand, the influence of a co-monomer addition in the sphere size was also analyzed. The suitable selection of the initiator type and its concentration, as well as the surfactant agent amount, led to a controlled obtainment of the polystyrene microspheres, appropriate to be used as template in the synthesis of hollow spherical materials.Fil: Gorsd, Marina Noelia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Blanco, Mirta Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Pizzio, Luis Rene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentin

Synthesis and characterization of hollow silica spheres

The synthesis and characterization of mono-dispersed silica hollow spheres using polystyrene (PS) spheres as template from the hydrolysis and condensation of tetraethylorthosilicate (TEOS) is presented. Successive washing steps with toluene and subsequent calcination at different temperatures were performed, in order to remove the PS template. Furthermore, the PS core removal was studied using different calcination temperatures, but without the prior washing with toluene. The morphology of the materials was studied by scanning electron microscopy and by transmission electron microscopy. A shell formed by silica nanoparticles with 50 nm diameter, being the layer of 100 nm thickness, was observed when using a low concentration of catalyst in the sol-gel reaction. The textural properties of the silica coating, obtained from N2 adsorption-desorption isotherms, depend on the catalyst amount added for the TEOS hydrolysis. From the Fourier transform infrared spectra and the results of the thermogravimetric analyses, it was found that the almost complete removal of the polystyrene core can be directly achieved by calcining at 500 °C, without the need of carrying out any washing and minimizing the formation of cracks in the silica hollow spheres.Fil: Gorsd, Marina Noelia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Pizzio, Luis Rene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Blanco, Mirta Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentin

Síntesis de microesferas nucleo/cubierta y esferas huecas de sílice para su uso como soporte de heteropoliácidos

Se sintetizaron microesferas nucléo/cubierta poliestireno/silice y microesferas huecas de silice empleando esferas de poliestireno (PS) como plantilla las cuales fueron recubiertas con sílice utilizando el método de Stöber modificado empleando tetraetilortosilicato (TEOS) como precursor. Para la obtención de las esferas huecas los sólidos fueron calcinados a 500 °C. Los materiales fueron impregnados mediante la técnica a humedad incipiente con ácido tungstofosfórico (TPA). Se observó por SEM un recubrimiento liso e uniforme de la capa de sílice de 100 nm de espesor determinada por TEM. Los sólidos presentaron isotermas de adsorción-desorción de N2 tipo IV y una fuerza ácida superior a 400 mV. Además en los espectros FT-IR de los sólidos impregnados se observó la presencia del anión tugstofosfato con estructura Keggin.Facultad de Ciencias Agrarias y Forestale

Síntesis de microesferas nucleo/cubierta y esferas huecas de sílice para su uso como soporte de heteropoliácidos

Se sintetizaron microesferas nucléo/cubierta poliestireno/silice y microesferas huecas de silice empleando esferas de poliestireno (PS) como plantilla las cuales fueron recubiertas con sílice utilizando el método de Stöber modificado empleando tetraetilortosilicato (TEOS) como precursor. Para la obtención de las esferas huecas los sólidos fueron calcinados a 500 °C. Los materiales fueron impregnados mediante la técnica a humedad incipiente con ácido tungstofosfórico (TPA). Se observó por SEM un recubrimiento liso e uniforme de la capa de sílice de 100 nm de espesor determinada por TEM. Los sólidos presentaron isotermas de adsorción-desorción de N2 tipo IV y una fuerza ácida superior a 400 mV. Además en los espectros FT-IR de los sólidos impregnados se observó la presencia del anión tugstofosfato con estructura Keggin.Facultad de Ciencias Agrarias y Forestale

Síntesis de microesferas nucleo/cubierta y esferas huecas de sílice para su uso como soporte de heteropoliácidos

Se sintetizaron microesferas nucléo/cubierta poliestireno/silice y microesferas huecas de silice empleando esferas de poliestireno (PS) como plantilla las cuales fueron recubiertas con sílice utilizando el método de Stöber modificado empleando tetraetilortosilicato (TEOS) como precursor. Para la obtención de las esferas huecas los sólidos fueron calcinados a 500 °C. Los materiales fueron impregnados mediante la técnica a humedad incipiente con ácido tungstofosfórico (TPA). Se observó por SEM un recubrimiento liso e uniforme de la capa de sílice de 100 nm de espesor determinada por TEM. Los sólidos presentaron isotermas de adsorción-desorción de N2 tipo IV y una fuerza ácida superior a 400 mV. Además en los espectros FT-IR de los sólidos impregnados se observó la presencia del anión tugstofosfato con estructura Keggin.Facultad de Ciencias Agrarias y Forestale

Synthesis and characterization of hollow silica spheres

The synthesis and characterization of mono-dispersed silica hollow spheres using polystyrene (PS) spheres as template from the hydrolysis and condensation of tetraethylorthosilicate (TEOS) is presented. Successive washing steps with toluene and subsequent calcination at different temperatures were performed, in order to remove the PS template. Furthermore, the PS core removal was studied using different calcination temperatures, but without the prior washing with toluene. The morphology of the materials was studied by scanning electron microscopy and by transmission electron microscopy. A shell formed by silica nanoparticles with 50 nm diameter, being the layer of 100 nm thickness, was observed when using a low concentration of catalyst in the sol-gel reaction. The textural properties of the silica coating, obtained from N2 adsorption-desorption isotherms, depend on the catalyst amount added for the TEOS hydrolysis. From the Fourier transform infrared spectra and the results of the thermogravimetric analyses, it was found that the almost complete removal of the polystyrene core can be directly achieved by calcining at 500 °C, without the need of carrying out any washing and minimizing the formation of cracks in the silica hollow spheres.Centro de Investigación y Desarrollo en Ciencias Aplicada

Synthesis and characterization of tungstophosphoric acid-modified mesoporous silica nanoparticles with tuneable diameter and pore size distribution

Mesoporous silica nanoparticles were prepared in aqueous/organic phase using cetyltrimethylammonium bromide and polystyrene as organic templates. The morphology and crystalline phase of the products were characterized by scanning electron microcopy, transmission electron microscopy, X-ray diffraction, small angle X-ray scattering, and N₂ adsorption/desorption isotherm analysis. The octane/water ratio influenced the pore size distribution, the morphology and size of the nanospheres obtained. Transmission electron microscopy revealed that mesoporous silica nanoparticles with “blackberry-like structure” (MSN3, MSN4, MSN5, and MSN6 samples) were obtained using octane/water ratios in the range 0.007–0.35. They present small (in the range 5–6 nm) and large (in the range 28–34 nm) mesopores. Large mesopores were mainly generated by polystyrene, and their volume contribution was clearly higher than in the MSN1 and MSN2 samples. The structure and morphology of mesoporous silica nanoparticles solids impregnated with tungstophosphoric acid were similar to those of the mesoporous silica nanospheres used as support. In addition, the characterization of all the solids impregnated with tungstophosphoric acid by Fourier transform infrared and ³¹P nuclear magnetic resonance indicated the presence of undegraded [PW₁₂O₄₀]³⁻ and [H3−XPW₁₂O₄₀](3−X)− species interacting electrostatically with the ≡Si–OH₂⁺ groups, and by potentiometric titration the solids presented very strong acid sites. In summary, they are good candidates to be used in reactions catalyzed by acids, especially to obtain quinoxaline derivatives.Facultad de Ciencias ExactasCentro de Investigación y Desarrollo en Ciencias Aplicada