Browsing by Author "Lapa, Hugo"
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- C-scorpionate Au(III) complexes as pre-catalysts for industrially significant toluene oxidation and benzaldehyde esterification reactionsPublication . Lapa, Hugo; Guedes Da Silva, M. Fátima C.; Pombeiro, Armando; Alegria, Elisabete; Martins, LuisaThe new Au(III) complex [AuCl2(Tpms)] (1) and the previously reported [AuCl2(Tpm)]Cl (2), bearing the potentially tridentate ligands tris(1-pyrazolyl)methanesulfonate (SO3C(C3H3N2)(3)(-), Tpms) or hydrotris(1-pyrazolyl) methane (HC(C3H3N2)(3), Tpm), respectively, were synthesized in water at room temperature and characterized using NMR and IR spectroscopy. The molecular structure of 1 was authenticated by single crystal X-ray diffraction analysis. The catalytic performance of the Au(III) complexes was tested, for the first time, in toluene and benzyl alcohol oxidation reactions. The oxidative esterification of benzaldehyde, by-product of toluene oxidation, was further explored. In order to optimize the catalytic systems, the influence of parameters such as temperature, reaction time, amount of pre-catalyst and the presence of additives was evaluated. In the peroxidative (by H2O2 or t-BuOOH) oxidation reactions, a maximum total yield (benzylic alcohol and benzaldehyde) of 8% for toluene oxidation with pre-catalyst 1 (6 h, 80 degrees C, H2O2 30% aq. sol.) and a maximum total yield (benzaldehyde and benzoic acid) of 43% for benzyl alcohol oxidation with pre-catalyst 2 (24 h, 80 degrees C, t-BuOOH 70% aq. sol.) with a selectivity of 72% for benzaldehyde, were obtained. The esterification of benzaldehyde yielded, in the presence of 1, a maximum of 27% and 48% of methyl benzoate, at room temperature and 80 degrees C, respectively, and with a selectivity of 78% for methyl benzoate.
- Catalytic oxidation of a model volatile organic compound (toluene) with tetranuclear Cu(II) complexesPublication . Sutradhar, Manas; Alegria, Elisabete; Roy Barman, Tannistha; Lapa, Hugo; Guedes Da Silva, M. Fátima C.; Pombeiro, ArmandoA tetranuclear Cu(II) cubane [Cu-2(mu-1 kappa ONO':2 kappa OO':3 kappa O-HL)(mu-1 kappa ONO':2 kappa OO'-HL)](2).4dmf (1) derived form (2,3-dihydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) was synthesized at room temperature and characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction. The known tetranuclear Cu(II) open-cubane [Cu(HL)](4).4EtOH (2) was synthesized from the same pro-ligand following a similar method or the reported one. The different tautomeric forms (keto and enol) of the organic ligands in 1 and 2 explain their different structural features. Both complexes were screened as catalysts for the peroxidative oxidation of toluene with tert-butyl hydroperoxide, achieving benzaldehyde and o-cresol as the main products. Complex 1 exhibits the highest activity (maximum product yield of 11%).
- Green synthesis of gold nanoparticles and their deposition on ITO surfacesPublication . Lapa, Hugo; Silva, Nelson; Fantoni, Alessandro; Maçarico, A. Filipe; Almeida, Gabriela; Alegria, ElisabeteThe use of plasmonic nanoparticles for biomedical applications has been widely explored, resulting in significant advances in the construction of optical biosensors. The shape and size of AuNPs determines the spectral signature of their Localized Surface Plasmon Resonance (LSPR) and, therefore, the features of their plasmonic band can be used to monitor surface changes such as those related to protein binding or nanoparticle aggregation. In this work, gold nanoparticles (AuNPs) were produced based on a green and sustainable methodology using tea leaves. The phytochemicals present in tea act as reducing and stabilizing agents. To optimize the AuNPs deposition (nanomaterial proximity, homogenization and substrate coverage), ITO surfaces were modified with different materials, namely sol-gel matrices (e.g. (3-aminopropyl) triethoxysilane (APTES)), cross-linking agents (e.g., glutaraldehyde) and biopolymers (e.g., Bovine Serum Albumin (BSA)). The produced AuNPs were deposited directly onto ITO surfaces functionalized with APTES or in a mixture of BSA and glutaraldehyde; these matrices are transparent and thus suitable for optical applications. The functionalization procedure of ITO surfaces with the referred materials was performed by two methodologies: i) direct deposition of the matrix solution using a micropipette and ii) ultrasound irradiation. The resulting functionalized ITO surfaces were compared and characterized by light transmission spectroscopy. Accordingly, the tea-AuNPs deposited in the presence of BSA and glutaraldehyde provided the best plasmonic response, being the most promising ones for the development of an optical immunosensor.
- p-xylene oxidation to terephthalic acid: new trendsPublication . Lapa, Hugo; Martins, LuisaLarge-scale terephthalic acid production from the oxidation of p-xylene is an especially important process in the polyester industry, as it is mainly used in polyethylene terephthalate (PET) manufacturing, a polymer that is widely used in fibers, films, and plastic products. This review presents and discusses catalytic advances and new trends in terephthalic acid production (since 2014), innovations in terephthalic acid purification processes, and simulations of reactors and reaction mechanisms.