Examinando por Autor "Morales Torres, Sergio"

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  • Miniatura
    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).
  • Miniatura
    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 Elena
    A 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.
  • Miniatura
    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 Elena
    Transition 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.