Persona: Pérez Mayoral, María Elena
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Pérez Mayoral
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Publicación Enhanced Catalytic Performance of ZnO/Carbon Materials with Highly Dense Active Sites in the Green Synthesis of Poly-substituted Quinolines(Elsevier, 2022-02) Godino Ojer, Marina; Morales Torres, Sergio; Pérez Mayoral, María Elena; Maldonado Hódar, Francisco J.A highly efficient methodology for the selective synthesis of nitrogen heterocycles via Friedländer reaction using carbon materials supported ZnO catalysts under the green chemistry domain is presented. The influence of the physicochemical properties of different carbon supports, in particular an activated carbon (AC), multi-walled carbon nanotubes (MWCNT) and a carbon aerogel (CA), on the catalytic performance is discussed. The developed catalysts are easily prepared by simple incipient wetness impregnation and a subsequent thermal treatment. These ZnO/carbon catalysts showed a great performance in the Friedländer condensation of 2-amino-5-chlorobenzaldehyde and carbonylic compounds with enolizable hydrogens, under solvent-free and mild conditions, affording in all cases selectively a total conversion to the corresponding quinoline. Both the Zn loading in combination with the developed microporosity of the selected carbon supports seem to be the key factors determining the catalytic performance. Yields obtained with ZnO/carbon composites catalysts are superior to those obtained by others widely used in fine chemistry such as, Zn-catalysts supported on mesoporous silica (SBA-15) and Zn-metal-organic-frameworks (MOF).Publicación Towards selective synthesis of quinoxalines by using transition metals-doped carbon aerogels(Elsevier, 2023-11-01) Godino Ojer, Marina; Morales Torres, Sergio; Maldonado Hódar, Francisco J.; Pérez Mayoral, María ElenaTransition metal (TM)-carbon aerogels, where TM = Mo, Fe, Co or Cu, were found to be active and selective catalysts for the synthesis of quinoxalines 1, from o-phenylenediamine 2 and α-hydroxy ketones 3, becoming an efficient and sustainable alternative to other carbon-based catalysts or even MOF. Doping metal phase consisting of the corresponding metal oxides but also as zero-valent metals depending on the metal and carbonization temperature, and metal loading at the surface of carbon aerogel are key factors conditioning both reactivity and selectivity. Although metal oxides are probably the predominant active catalytic species, zero-valent metals nanoparticles (Cu0 or Co0) could be implied in the last dehydrogenation step of the reaction. Moreover, the additional functionalization with oxygenated surface groups (Co-1000PO catalyst) resulted on an enhanced reactivity probably due to the cooperation between both functions. Remarkably, Mo-500 catalyst was the most efficient sample selectively leading to the quinoxaline 1a in high conversion. Finally, our results strongly suggest different operative pathways when using TM-doped carbon aerogels depending on the metallic phase at the carbon surface. While TM-doped carbon aerogels (where TM = Fe, Co, or Cu) probably act catalyzing a sequential acid-base steps and subsequent aromatization leading to the corresponding quinoxaline 1a, Mo-doped catalyst would work via the initial oxidation of α-hydroxy ketones followed by condensation-dehydration reactions.Publicación Porous carbons-derived from vegetal biomass in the synthesis of quinoxalines. Mechanistic insights(Elsevier, 2020-09-01) Godino Ojer, Marina; Blazquez García, R.; Matos, Ines; Bernardo, M.; Fonseca I.M.; Pérez Mayoral, María ElenaWe report herein for the first-time acid biomass-derived carbons from vegetal biomass, with high developed porosity, prepared through integrating method comprising pyrolysis and surface phosphonation, able to efficiently catalyze the synthesis of quinoxalines from 1,2-diamines and α-hydroxi ketones, under aerobic conditions. The obtained results indicate that the reaction is mainly driven by a combination of acid function strength and textural properties in terms of conversion and selectivity. Furthermore, our experimental and theoretical observations suggest that the preferred reaction pathway for this transformation, in the presence of the investigated acid carbon catalysts, involves cascade reactions including imination reaction between reactants, successive imine-enamine and keto-enol tautomerisms, heterocyclization followed by dehydration, and aromatization. While the acid sites seem to be a relevant role in each reaction step, the system formed by activated carbon and molecular oxygen could be behind the last oxidative reaction to give the corresponding nitrogen heterocycles.Publicación Acidic porous carbons involved in the green and selective synthesis of benzodiazepines(Elsevier, 2020-11-01) Godino Ojer, Marina; Matos, Ines; Bernardo, M.; Carvalho, R.; G.P. Soares, Olívia Salomé; Durán Valle, C.; Fonseca, I.M.; Pérez Mayoral, María ElenaEco-sustainable and recyclable porous carbons are reported as metal-free catalysts for the synthesis of benzodiazepines for the first time. The porous carbons were able to efficiently catalyse the synthesis of benzodiazepine 1 from o-phenylendiamine 2 and acetone 3 under mild conditions. Both acidic functions and the porosity of the catalysts were determinant features. High conversion values were obtained when using HNO3 oxidized carbons. The highest selectivity to benzodiazepine 1 was obtained in the presence of the most microporous catalyst N-N, which is indicative of the great influence of porous properties. Stronger acid sites and high microporosity of the carbon treated with H2SO4 yield benzodiazepine 1 with total selectivity.Publicación Amino-grafted basic mesoporous silicas: a type of highly performant catalysts for the green synthesis of 2-amino-4H-chromenes(Elsevier, 2024-03-15) González Rodal, Daniel; Godino Ojer, Marina; Palomino Cabello, Carlos; Turnes Palomino, Gemma; López Peinado, Antonio José; Pérez Mayoral, María ElenaNovel series of amino-grafted mesoporous silica materials applied to the green and efficient synthesis of 2-amino-4H-chromenes, from salicylaldehydes and ethyl cyanoacetate, under mild and free-solvent conditions, is herein reported for the first time. These catalysts are easily prepared by using the post-synthetic method, by functionalizing the SBA-15 silica with the corresponding amino silanes. The observed catalytic performance is mainly controlled by the type and concentration of basic sites. The methodology herein reported could be considered as an environmentally friendly alternative for the selective chromene synthesis, which allows to achieve high yields in short reaction times using notably small amounts of the catalysts. The experimental results are also supported with theoretical calculations, which suggest that the amine groups at the silica surface are behind the observed catalytic performance with the assistance of the silica matrix.Publicación Basolites: A type of Metal Organic Frameworks highly efficient in the one-pot synthesis of quinoxalines from α-hydroxy ketones under aerobic conditions(Elsevier, 2020-04-01) Godino Ojer, Marina; Shamzhy, Mariya; Čejka, Jiři; Pérez Mayoral, María ElenaWe report here efficient synthesis of quinoxalines from o-phenylendiamine and α-hydroxy ketones over commercial Basolites. The concentration and type of acid centres, as CUS sites, together with the porosity of the samples strongly influence the resulting conversion and selectivity. Our results indicate that the formation of quinoxalines preferentially follows a new route, in which tautomerization reactions are also involved.Publicación P-Doped carbon catalyst highly efficient for benzodiazepine synthesis. Tires valorisation(Elsevier, 2023-07-01) Godino Ojer, Marina; Ripoll Morales, Vanessa; López Peinado, Antonio José; Matos, Inés; Bernardo, María; Lapa, Nuno; Fonseca, Isabel M.; Pérez Mayoral, María ElenaCarbon catalysts prepared from pyrolysis of spent tires are found to efficiently catalyse the synthesis of benzodiazepine 1, from o-phenylendiamine 2 and acetone 3, with high conversions and selectivity, under mild reaction conditions, according to Scheme 1. The most acidic catalyst, CPN_H3PO4, obtained by chemical activation with H3PO4, resulted on the most efficient catalyst affording conversion values higher than 90 %, after 4 h of reaction time, and selectively leading to benzodiazepine 1 (90 %). On the other hand, the CPN and CPN_CO2 catalysts reached high conversions of 2 although diminished selectivity to 1, confirming that the carbon matrix is involved in the first steps of the reaction mainly catalyzing the formation of intermediate 4 as the main reaction product. Note that all the investigated catalysts are macroporous materials with pore size distribution large enough to favor diffusion of reactants and products. Therefore, the catalytic performance is mainly governed by the chemical surface, in particular by the presence of acid functions as phosphate groups anchored to the carbon surface or as SiP2O7 supported phase. Finally, considering both experimental and theoretical results, it seems that the most probable catalytic centers comprise phosphate functions in SiP2O7 catalyzing the last cyclization step to 1. Although electrophilicity of carbon acceptor (Cdouble bondN moiety) in the presence of model simulating phosphate groups anchored to the carbon surface was slightly superior, transition structure in the presence of model simulating SiP2O7 showed the smallest free energy barrier.Publicación Highly efficient carbon catalysts for the green synthesis of 1,5-benzodiazepine: experimental and theoretical study(Elsevier, 2024-04-15) Godino Ojer, Marina; Ripoll Morales. Vanessa; Pastrana martínez, Luisa M.; Morales Torres, Sergio; Maldonado Hódar, Francisco J.; Pérez Mayoral, María ElenaA family of sustainable carbon catalysts with different chemical surface, active and selective for the synthesis of benzodiazepine 1 (BDZ), from o-phenylendiamine (OPD) 2 and acetone 3, under mild conditions, is reported. Catalysts were prepared by acids treatments with H2SO4 or H3PO4 of an activated carbon doped with ZnO at 3% wt (N3Zn) and, subsequently, submitted to additional thermal treatment in air. Simultaneously to the ZnO leaching, surface C-SO3 groups were generated by treatment of N3Zn with H2SO4 (N3Zn-S) whereas treatment with H3PO4 led to C-PO3 functions (N3Zn-P sample). The thermal treatment partially removes the C-SO3 groups (N3Zn-S-C sample) while C-PO3 functions were partially oxidized to C-OPO3 groups (N3Zn-P-C). Our results suggest that these chemical surface modifications of the catalysts are key on catalytic performance, pointed out the importance of the nature and distribution of acid sites at the surface. Remarkably, investigated carbon catalysts (N3Zn-S samples) were more active than the NS catalyst obtained by direct treatment of AC with H2SO4, this last mainly functionalized with C-OSO3 groups. Although the catalysts resulting of the H3PO4 treatment showed both a similar activity, some differences on selectivity to BDZ 1 were observed, attributed to certain specificity of P-functions at the surface depending on the acid strength of active sites and the reaction conditions. These results were supported by DFT calculations.