Recent Applications of Heteropolyacids and Related Compounds in Heterocycle Synthesis. Contributions between 2010 and 2020

Over the past two decades, polyoxometalates (POM) have received considerable attention as solid catalysts, due to their unique physicochemical characteristics, since, first, they have very strong Bronsted acidity, approaching the region of a superacid, and second, they are efficient oxidizers that exhibit rapid redox transformations under fairly mild conditions. Their structural mobility is also highlighted, since they are complex molecules that can be modified by changing their structure or the elements that compose them to model their size, charge density, redox potentials, acidity, and solubility. Finally, they can be used in substoichiometric amounts and reused without an appreciable loss of catalytic activity, all of which postulate them as versatile, economic and ecological catalysts. Therefore, in 2009, we wrote a review article highlighting the great variety of organic reactions, mainly in the area of the synthesis of bioactive heterocycles in which they can be used, and this new review completes that article with the contributions made in the same area for the period 2010 to 2020. The synthesized heterocycles to be covered include pyrimidines, pyridines, pyrroles, indoles, chromenes, xanthenes, pyrans, azlactones, azoles, diazines, azepines, flavones, and formylchromones, among others

An Efficient Protocol for the Synthesis of Quinoxaline Derivatives at Room Temperature Using Recyclable Alumina-Supported Heteropolyoxometalates

We report a suitable quinoxaline synthesis using molybdophosphovanadates supported on commercial alumina cylinders as catalysts. These catalysts were prepared by incipient wetness impregnation. The catalytic test was performed under different reaction conditions in order to know the performance of the synthesized catalysts. The method shows high yields of quinoxaline derivatives under heterogeneous conditions. Quinoxaline formation was obtained using benzyl, o-phenylenediamine, and toluene as reaction solvent at room temperature. The CuH2PMo11VO40 supported on alumina showed higher activity in the tested reaction. Finally, various quinoxalines were prepared under mild conditions and with excellent yields

Ternary Hydrotalcites in the Multicomponent Synthesis of 4H-Pyrans

Lamellar double hydroxides (LDH) with double divalent cations were synthesized by the co-precipitation method and studied in the multicomponent synthesis of 4H-pyrans. The solids obtained were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), N2 adsorption isotherms, and thermogravimetric analysis (TGA). The XRD patterns confirmed the formation of LDHs in which the incorporation of Ni2+ or Co2+ improves their crystalline and textural properties. The results of catalytic activity showed that the synthesis of 4H-pyrans is favored in solvent-free conditions with the LDH–Ni catalyst, avoiding calcination processes. In addition, it was found that hydrotalcite with double divalent cations can conduct this reaction through multicomponent synthesis or by the Michael addition reaction, which can be performed by different types of basicity that depend on the composition of another divalent cation in the brucite layer or a calcination process

Relationships between Kováts Retention Indices and Molecular Descriptors of 1-(2-Hydroxy)-3-Arylpropane-1,3-Diones

Experimental and theoretical results for retention index of a set of 20 beta-diketones are given. The quantitative structure-chromatographic retention relationships (QSRR) theory is employed and six molecular descriptors are chosen to compute the fitting polynomials. Multiple regression analysis yields satisfactory results when one resorts to several variables equations, instead of computing just one-variable formulae. Average absolute deviations from experimental results are rather low, which seems to point out the suitability of the present approach

Heteropolycompounds as catalysts for biomass product transformations

[EN] In the present review we show a variety of biomass product transformations through catalysis by both bulk and supported heteropolycompounds. The biomass sources considered include carbohydrates, oils and fats, and terpenes as main starting material groups. The products obtained and their applications are presented.We thank CONICET (PIP 003), Agencia Nacional de Promocion Cientifica y Tecnologica (Argentina) (PICT 0406), and Universidad Nacional de La Plata for financial support. GPR and HJT are members of CONICET. MJC and SI thank to Spanish Government-MINECO through Consolider Ingenio 2010-Multicat project for financial support.Sanchez, LM.; Thomas, HJ.; Climent Olmedo, MJ.; Romanelli, GP.; Iborra Chornet, S. (2016). Heteropolycompounds as catalysts for biomass product transformations. Catalysis Reviews: Science and Engineering. 58(4):497-586. doi:10.1080/01614940.2016.1248721S49758658

Whey as an Alternative Nutrient Medium for Growth of Sporosarcina pasteurii and Its Effect on CaCO3 Polymorphism and Fly Ash Bioconsolidation

Whey in large quantities can cause environmental problems when discarded, because it reduces dissolved oxygen and aquatic life. Nonetheless, it could be used as an easily available and economical alternative to reduce culture medium costs in microbially induced calcium carbonate precipitation (MICP). In this work, a native Sporosarcina pasteurii was isolated and then cultured by using different proportions of whey (W) in nutrient broth (NB). The solids were characterized by XRD, FT-IR, TGA, and SEM. The potential applications in bioconsolidation were also studied. Whey concentration was directly related to CaCO3 production. Higher whey concentrations reduced calcium carbonate purity to nearly 80%. All experiments showed calcite and vaterite fractions, where a whey increment in the media increased calcite content and decreased vaterite content, causing a decrease in crystal size. MICP improved compressive strength (CS) in sand and fly ash. The best CS results were obtained by fly ash treated with 25 W-75 NB (37.2 kPa) and sand with 75 W-25 NB (32.1 kPa). Whey changed crystal polymorphism in biogenic CaCO3 production. Material bioconsolidation depends on the CaCO3 polymorph, thus fly ash was effectively bioconsolidated by crystallization of vaterite and sand by crystallization of calcite

Chemoselective Reductive Heterocyclization by Controlling the Binomial Architecture of Metal Particles and Acid−Base Properties of the Support

2,1-Benzisoxazoles have been selectively synthesized through reductive heterocyclization of 2-nitroacylarenes using Pt-supported nanoparticles. The reaction involves a cascade process in which the first step is the reduction of the nitro group into hydroxylamine followed by heterocyclization through the nucleophilic attack of the hydroxylamine group to the carbonyl of the acyl group and further dehydration. The reaction was performed on Pt/C, Pt/TiO2, and Pt/MgO using hydrogen as the reducing agent under mild reaction conditions. The results showed that Pt/MgO was the most active and selective catalyst. The study of the influence of the crystal size of the metal on the activity and selectivity, combined with the reaction mechanism examined by in situ Fourier transform infrared spectroscopy of the adsorbed reactant, showed that the maximum activity and selectivity to the target compound can be achieved by controlling the architecture of metal particles and acid–base properties of the support. The effect of temperature on selectivity, the stability of the Pt/MgO catalyst, and the scope of the reaction have been studied. Finally, reductive heterocyclization using different metals (Pd and Au) supported on MgO has also been performed.Centro de Investigación y Desarrollo en Ciencias Aplicada

Role of vanadium and pyridine in heteropolycompounds for selective oxidation of alcohols with hydrogen peroxide

This study describes the application of heteropolyacids H3PMo12O40,H4SiMo12O40, H4PMo11VO40, H5PMo10V2O40, H9PMo6V6O40, and a hybrid pyridine-modified heteropolyacid with Keggin structure for selective oxidation of alcohols to ketones or aldehydes using aqueous hydrogen peroxide and acetonitrile as solvent. Performance of these different catalysts in 1-phenylethanol oxidation was studied. Influence of reaction temperature, amount of catalyst and hydrogen peroxide and reaction time on the yield of acetophenone was investigated to obtain optimal reaction conditions. Oxidation ability of the catalyst depended on the number of vanadium atoms present in the Keggin ion and to a lesser extent on pyridine substitution in the Keggin secondary structure. In order to explore the applicability of the method for selective oxidation of alcohols to ketones or aldehydes, various alcohols were investigated according to the general procedure using hybrid pyridine-modified heteropolyac

P-Sulfonic acid calix[4]arene-functionalized alkyl-bridged organosilica in esterification reactions

Two new p-sulfonic acid calix[4]arene- and p-sulfonic acid calix[6]arene-functionalized organosilica have been synthesized using a sol-gel method and applied as heterogeneous catalysts in esterification reactions. The catalytic performance was evaluated using the esterification of carboxylic acids with ethanol, and good catalytic activity (i.e., 55-88%) was observed under the optimum reaction conditions. This study reports the first promising example of the successful employment of calix[n]arenes as a heterogeneous catalyst for catalytic esterification. The catalyst was easily separated by filtration and reused five times without any significant loss of activity.Fil: De Assis, J. V.. Universidade Federal de Viçosa; BrasilFil: Abranches, P. A. S.. Universidade Federal de Viçosa; BrasilFil: Braga, I. B.. Universidade Federal de Viçosa; BrasilFil: Portilla Zúñiga, Omar Miguel. 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: Sathicq, Angel Gabriel. 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: Romanelli, Gustavo Pablo. 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: Sato, A. G.. Universidade Federal de Viçosa; BrasilFil: Fernandes, S. A.. Universidade Federal de Viçosa; Brasi

EVALUACIÓN DE LA CAPACIDAD DE INDUCCIÓN DE ANTIXENOSIS DE DOS COMPUESTOS (CINAMATO DE METILO Y ETILO) PARA CONTROLAR AL PULGÓN VERDE DE LOS CEREALES EN AVENA

La avena es el principal cereal invernal empleado como verdeo en nuestro país, cuya producción y rendimiento está afectada entre otros factores, por la presencia del pulgón verde (Schizaphis graminum). El manejo inadecuado de productos fitosanitarios ha tenido numerosas consecuencias negativas, por lo que es imperante buscar alternativas sustentables, y la integración e implementación de diferentes estrategias de control de insectos plagas tales como el uso de cultivares tolerantes y el empleo de compuestos orgánicos que apliquen los postulados de la Química Verde. Los defensas inducidas son aquellas que se generan cuando la planta detecta que está siendo atacada por patógenos y /o insectos plaga, este mecanismo esta mediado por algunas fitohormonas [1, 2], entre ellas el ácido salicílico (AS), quien tiene un rol esencial en la activación de genes de defensas que codifican para proteínas PR (proteínas asociadas a la patogénesis), y de respuesta hipersensible (RH) [3]. Se definió la antixenosis como la capacidad de las plantas de no compatibilizar con el insecto, evitando que el insecto la utilice para oviposición, alimento o refugio [4]. El Objetivo fue evaluar la capacidad de inducción de antixenosis de dos compuestos orgánicos precursores del AS (R1: cinamato de metilo y R2: cinamato de etilo), sintetizados mediantes procedimientos de bajo impacto ambiental. Se utilizaron 16 cultivares de avenas obtenidas en la CEI de Barrow y dos compuestos orgánicos R1 y R2, cuya preparación se realizó bajo procesos sustentables en la cátedra de Química Orgánica. La evaluación de antixenosis en los 16 cultivares se realizó mediante la prueba de libre selección de hospedero, en condiciones controladas de Tº, y fotoperíodo (22± 1°C; 12:12 L: O). En el estado de segunda hoja expandida (Zadok Z: 1.2) se formó un circulo con los 16 cultivares, en el centro del mismo se colocaron aproximadamente entre 7- 10 hembras ápteras adultas. A las 24 hs de la infestación se hizo el recuento del Nº áfido por cada planta. Se empleó un diseño complemente aleatorizado con 10 repeticiones (10 círculos), la ubicación de cada variedad fue sorteada al azar, hubo tres tratamientos (Testigo, R1 y R2). Se aplicó una dilución de 1x10-5 M en R1 y R2, y con Tween20 y agua en el grupo Testigo, mediante aspersión exógena hasta chorreo, 24 h antes de la infestación con los insectos, luego, se realizó el conteo del Número de insectos por planta. Los datos de los experimentos se analizaron por separado mediante análisis de varianza (ANOVA) y las medias de los distintos cultivares se compararon usando el Test de Tukey. Para un mejor ajuste a la normalidad, los datos fueron transformados con la fórmula Log (X+1). La aplicación del análisis de la varianza demostró la presencia de diferencias altamente significativas solamente para Tratamientos con los dos compuestos orgánicos (tablas 1 y 2). En el tratamiento con R1 se observó que los cultivares Nº 9 y el Nº 13 vieron mejorada significativamente su antixenosis, al condicionar un menor número de insectos por planta en relación al testigo, mientras que los restantes cultivares no modificaron tal condición (figura Nº 1). En tanto, en el tratamiento con R2, los cultivares Nº 1, 3, 4, 6, 9 y 12 mostraron un menor número de insectos por planta en relación al testigo, resultando ser más antixenoticos (figura Nº2). El único cultivar que respondió con ambos tratamientos (R1 y R2) fue el Nº 9. Se sugiere que los cambios observados en el nivel de antixenosis en los materiales estudiados podrían ser atribuidos al tratamiento con los compuestos orgánicos. Los resultados indicarían mejor efectividad en el control de los áfidos del cinamato de etilo (R2), sin embargo se sugieren más estudios para corroborar su acción repelente. La aplicación del análisis de la varianza demostró la presencia de diferencias altamente significativas solamente para Tratamientos con los dos compuestos orgánicos (tablas 1 y 2). En el tratamiento con R1 se observó que los cultivares Nº 9 y el Nº 13 vieron mejorada significativamente su antixenosis, al condicionar un menor número de insectos por planta en relación al testigo, mientras que los restantes cultivares no modificaron tal condición (figura 1). En tanto, en el tratamiento con R2, los cultivares Nº 1, 3, 4, 6, 9 y 12 mostraron un menor número de insectos por planta en relación al testigo, resultando ser más antixenoticos (figura 2). El único cultivar que respondió con ambos tratamientos (R1 y R2) fue el Nº 9. Se sugiere que los cambios observados en el nivel de antixenosis en los materiales estudiados podrían ser atribuidos al tratamiento con los compuestos orgánicos. Los resultados indicarían mejor efectividad en el control de los áfidos del cinamato de etilo (R2), sin embargo se sugieren más estudios para corroborar su acción repelente