Catalytic aldol condensations of bio-derived aldehydes and ketones
- Autores: Alberto Tampieri
- Directores de la Tesis: Francesc Medina Cabello (dir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2022
- Idioma: inglés
- Tribunal Calificador de la Tesis: Didier Tichit (presid.), Sandra Contreras Iglesias (secret.), Stefania Albonetti (voc.)
- Programa de doctorado: Programa de Doctorado en Nanociencia, Materiales e Ingeniería Química por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Chapter 1 is a technical introduction to the rest of the thesis. The environmental impact of human activities, especially of the chemical industry, is described. Sustainable and green chemistry are presented as possible solution to the environmental changes, and the role of catalysis in reaching the sustainability goals is scrutinized. The benefits and the current state of biorefining are examined, focusing on the platform molecules discussed in this thesis. The potential of aldol condensation as a processing tool for bio-derived chemicals and of hydrotalcites and derivatives as solid basic catalyst for the reaction is analysed.
In Chapter 2, the aldol condensation between furfural and acetone over basic 2:1 Mg:Al hydrotalcite-based materials under microwave irradiation is described. The prepared solids were characterized by PXRD, ICP-AES, TGA-DSC and N2 physisorption, and tested as catalysts at a number of reaction conditions. Following the commonly observed activity trend, the hydrotalcite prepared by co-precipitation was the least active, followed by the corresponding mixed metal oxide obtained by calcination, while the meixnerite-type material obtained upon dehydration proved to be the most active catalyst. The reaction is quite fast and selective towards the desired condensation products.
In Chapter 3, an analogous process with 5-hydroxymethyl furfural (HMF) and acetone is described. A more complete catalyst characterization (PXRD, ICP-AES, ESEM-EDX, TEM, FT-IR and Raman spectroscopy, N2 physisorption, CO2 chemisorption and TGA-MS) is included, and the final reaction mixtures were analysed by GC-FID and -MS, HPLC-DAD and -TOF, and NMR, which was also used to determine the stereoconfiguration of the obtained products, suggesting that our process is completely E-selective. This time, the activity of mixed metal oxide was surprisingly low, even less than the one of the parent hydrotalcite, while the meixnerite was again the most active catalyst; high conversions were obtained in very short times with relatively low catalyst loadings. Different catalyst recycle strategies have been explored, and the meixnerite was recycled with low activity loss.
Chapter 4 contains the research that was performed in collaboration with Prof. K. Föttinger and N. Barrabés from TU Wien, and is a research overview of the reaction of acetone with furfural and HMF that actively tackles the standing challenges of the research field. The catalytic reactions of the two aldehydes are compared, highlighting the importance of using impurity-free reagents, showing how furfural appears to be more reactive, perhaps because of stronger adsorption of HMF-related species, as confirmed by the rate decrease of acetone’s self-condensation. The reaction species that we synthesized and purified (including C14, a novel hetero-double-condensation product) were used as spectroscopic standards to study the condensations and the deactivating deposited matter on the catalysts, proposing deactivation pathways: FT-IR and UV-Vis results pointed to the formation of highly conjugated C=C bonds that possibly correspond to polymers; the formation of this polymer was studied in greater detail by in situ/operando ATR-IR. NMR spectroscopy was extensively used to study the reaction in situ, to perform deuteration studies that enabled the detection of the elusive aldol intermediate of HMF, and to measure the mass diffusivity of the reaction components.
Chapter 5 is a critical assessment of the use of levulinic acid and its derivatives in aldol condensations; the results presented in this preliminary report are the starting point for further studies. While levulinic acid is incompatible with basic catalysis because of its carboxyl, the feasibility of using ethyl levulinate was extensively tested and ruled out because of ester hydrolysis. Sodium levulinate was then successfully employed in the condensation with furfural over NaOH and a hydrotalcite-derived mixed metal oxide; however, this approach requires an additional neutralization and acidification, and has multiple condensation products (among which are the isomeric β- and δ-C10 that were studied by GC-FID/MS) making this reaction less attractive than the condensations with acetone.
Chapter 6 contains the general conclusions of this thesis: we successfully developed aldol condensation protocols to combine acetone or sodium levulinate with furfural and/or HMF, based on hydrotalcite-based materials and implementing their recovery and recycling; thanks to our catalytic results and characterization studies, especially with IR and NMR, we increased the fundamental understanding of the functioning of our system and we decreased the gap to the complete elucidation of reaction and deactivation mechanisms.
The Annexes include the supplementary information to Chapter 4, the indexes of tables, figures and schemes in the text, the lists oof the events attended during the PhD, the contributions and the outcomes of this thesis, and the tables of all the known properties of the reaction compounds in this thesis, of the nomenclature rules used, of the reactivity and stability scales in organic chemistry, of the catalysts used, and a dedicated periodic table with information on the isotopes of interest.
