Mirta Blanco

Efficient Tetrahydropyranylation of Phenols and Alcohols Catalyzed by Supported Mo and W Keggin Heteropolyacids

Abstract The protection of phenols as tetrahydropyranyl acetals is studied using supported Keggin heteropolyacids as catalysts, specifically molybdophosphoric or tungstophosphoric acids supported on silica. Phenol tetrahydropyranyl acetals are obtained in short times at room temperature with excellent yields. Protection of alcohols is also performed under mild conditions using both supported heteropolyacids, with yields ranging between good and quantitative. The reactions are clean and their workup is very simple. The use of these solid catalysts allows replacing the usual soluble inorganic acids, contributing to waste reduction.

Transition metal-modified polyoxometalates supported on carbon as catalyst in 2-(methylthio)-benzothiazole sulfoxidation

AbstractPolyoxometalates with lacunary Keggin structure modified with transition metal ions [PW11O39 M(H2O)]5−, where M = Ni2+, Co2+, Cu2+ or Zn2+, were synthesized and supported on activated carbon to obtain the PW11MC catalysts. Using FT-IR and DTA-TGA it was concluded that the [PW11O39M(H2O)]5− species are interacting with the functional groups of the support, and that thermal treatment leads to the loss of the coordinatively bonded water molecules without any noticeable anion degradation. The activity and selectivity of the catalysts in the sulfoxidation reaction of 2-(methylthio)-benzothiazole, an emerging environmental pollutant, were evaluated. The reaction was carried out in acetonitrile as solvent using H2O2 35% p/v as a clean oxidant. The conversion values decreased in the following order: PW11NiC > PW11CuC > PW11CoC > PW11ZnC, with selectivity to sulfoxide higher than 69%. The catalyst could be reused without appreciable loss of the catalytic activity at least three times. The materials were found to be efficient and recyclable catalysts for 2-(methylthio)-benzothiazole sulfoxidation in order to obtain a more biodegradable product than the corresponding substrate. Graphical AbstractPolyoxometalates with lacunary Keggin structure-modified with transition metal ions [PW11O39M(H2O)]5-, where M= Ni2+, Co2+, Cu2+ or Zn2+, were synthesized and supported on activated carbon to obtain the PW11MC catalysts.

Hydrotreating catalysts on alumina, titania or zirconia from ethanol/water solutions of heteropolyacids

Abstract Supported PNiMo(W) catalysts for hydrodesulfurization and hydrodenitrogenation were prepared. Heteropolyacids were used as precursors and supported on alumina, titania and zirconia. The tungstophosphoric and molybdophosphoric acids showed a stable Keggin-type structure when the supports were zirconia and titania. However, the heteropolyacids on alumina were degraded during the drying and/or calcination of the impregnated samples. The, catalysts prepared, on alumina had the highest activity, in the order of commercial ones. The catalysts on titania, were more active than the samples supported on zirconia.

Use of new silica fillers as additives for polymers used in packaging of fruit

The objective of this work was to synthesize nanosilicas with different degree of hydrophobicity by the sol-gel method, using tetraethyl orthosilicate as a precursor. For this purpose, 3-aminopropyl triethoxysilane (APS) and 1,1,1,3,3,3 - hexamethyldisilazane (HMDS), were added during synthesis as modifiers. A commercial biopolymer (Hexamoll Dinch, BASF) intended for packaging of apples, was added to the new nanosilicas. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, potentiometric titration, porosity, specific surface area and hydrophobicity/hydrophilicity by wetting test. Colorimetry was used to evaluate change in apple pulp color after contact with the different silicas.

Improved antimicrobial activity of silica–Cu using a heteropolyacid and different precursors by sol–gel: synthesis and characterization

Antimicrobial coatings are used to avoid the proliferation of fungi and bacteria inside urban buildings by incorporating low concentrations of antimicrobial agents (biocides). This study is focused on evaluating the antifungal activity of copper (II) supported on a silica matrix, and as counter-cation of a heteropolyacid, obtained from the sol–gel method using various catalysts, against two fungal isolates. The fungi used in this evaluation were Alternaria alternata and Chaetomium globosum isolated by routine microbiological techniques from biodeteriorated paints films. In all cases, fungi were selected due to their ability to grow on the paint films and their negative impact on human health. First, silicas were prepared using tetraethylorthosilicate and methyl trimethoxysilane as precursors and acetic acid, hydrochloric acid as catalysts of the hydrolysis reaction of the alkoxide. The effect of addition of copper (II) in the form of copper nitrate was studied. With respect to the morphology of the silica, most of them are similar, between pure and modified silica, in all cases. Once the stage of the synthesis and characterization of the prepared materials was performed, six of them were selected to evaluate their antifungal activity by agar plate inhibition test against both fungi of interest (A. alternata and C. globosum), and the percent inhibition was determined in each case. Tested Cu-based solids were shown to have a higher antifungal activity because they completely inhibit the growth of both fungi with lower concentrations relative to its control. This work was performed as a preliminary study, in order to guide the selection of a suitable organic biocide from a list of possible antifungal agents.Graphical Abstract

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.Graphical Abstract

Polymer-immobilized aluminium or copper tungstophosphates and tungstosilicates as new catalysts in anisole acylation

New materials with spherical shape were obtained from aluminium or copper salts of tungstophosphoric and tungstosilicic acids immobilized in a polymeric blend prepared with polyvinyl alcohol and polyethylene glycol by the freeze-thawing method. It is observed that the salts retain the Keggin structure of the heteropolyanions during their synthesis and immobilization. There is an almost constant distribution of the salts along the sphere width when they are included in the PVA-PEG blend. Also, the immobilized salts present very strong acid sites. The catalytic activity in the anisole acylation of the immobilized aluminium salts was higher than that of the catalysts obtained from the copper salts.