Organocatalytic transformations of carbon dioxide and cyclic carbonates
- Autores: Sergio Sopeña Frutos
- Directores de la Tesis: Arjan Kleij (dir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Benjamin R. Buckley (presid.), Marcos García Suero (secret.), Giulia Fiorani (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología Química por la Universidad Rovira i Virgili
- Materias:
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- Resumen
Carbon dioxide is a natural compound necessary for life, but the concentration in the air is increasing so much and very fast due to the high amount of gas emitted to the atmosphere as a result of the anthropogenic activities. Thus, the number of technologies that take advantage of this waste are improving and moving fast from laboratory scale to bulk scale.
Carbon dioxide is also a very interesting compound that can be used as C1 building block in the synthesis of other substrates such as cyclic carbonates or carbamates. In general terms, this transformation requires high amounts of energy and the development of new catalytic processes that lower this energy barrier and make this transformation easy are highly demanded.
The following thesis is about new research related to the application of organocatalysts in the synthesis of cyclic carbonates and its later postmodification by their transformation in carbamates. This “green chemistry” is developed at laboratory scale (grams scale) using different king of autoclave/reactors depending on the experimental requeriments. (Autoclave, HEL reactor, AMTEC reactor, THE techniques) In the second chapter (tannic acid), the objective was to prove that the use of non expensive and readily available natural compounds could be used as organocatalyst in the synthesis of cyclic carbonates. This binary catalytic system proved to be highly efficient in the transformation of terminal epoxides. Furthermore, both, the activity and recyclability of the system was studied by comparison with other organocatalysts with the help of multi experiment platforms systems.
During the third chapter, other catalyst (squaramide) was applied to this transformation. Squaramides are very important organic compounds which properties (electrical, sterically, acidity, aggregation, solubility…) can be easily modulated in their synthesis like a puzzle. This catalytic system proved to be and excellent choice applied to the synthesis of cyclic carbonates, with very good results for terminal epoxides at room temperature. The kinetics of the reaction (obtained via autoclave reactor) prompted us to test their activity in more challenging transformations, for example, in the synthesis of internal cyclic carbonates. For those substrates, squaramides proved to be an excellent choice as well being a substrate scope of 10 compounds a good prove of that. The reaction mechanism was studied via NMR and UV-Vis spectroscopy with a series of titration and competition experiments. The results also support the existence of an alternative operating mechanism that is not involved in the activation of the epoxide, but in the stabilization of the oxo anions intermediates.
In the fourth chapter, we report a totally different approach towards the synthesis of tri and tetra substituted cyclic carbonates from epoxides and carbon dioxide. This methodology doesn´t require the use of a binary catalytic system because is based in the generation of an initial cyclic carbonate specie that equilibrates to a tri or tetra substituted cyclic carbonate under thermodynamic control (following a similar Payne rearrangement mechanism for epoxyalcohols). Then, this product is trapped in situ displacing the equilibrium to the final product.
Finally, in the last chapter, cyclic carbonates (mono, di, tri and tetra) can be used as precursors for the synthesis of carbamates and polyhydroxyurethanes. This protocol, based on the use of TBD as organocatalyst, not only allow the synthesis of carbamates in milder conditions, but also with a higher selectivity grade by solving the problem of the formation of two Regio isomers during the opening of the cyclic carbonate step. The following study shows the results of the application of this synthetic protocol to a wide range of substrates and substitutions with promising results.
