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No description available.

The work presented in this thesis falls into four parts. In Chapter 1 results are presented for the detritiation of a number of substituted 2-([3H]-acetyl) thiophenes. These show that when a carboxyl group is present adjacent to the ionising acetyl group intramolecular catalysis makes an important contribution to the overall rate although the effective molarity is no higher than the other base catalysed proton transfers previously reported in the literature. Proton transfer reactions involving the ionisation of carbon acids have usually been studied in aqueous conditions. In Chapter 2 the development of a detritiation procedure for non-aqueous conditions is reported and the method used to establish an order of basicity for a large number of amines in dimethyl sulphoxide. The following chapter extends the investigation carried out in Chapter 2 to a range of other solvents. The results show a marked similarity in relative rates for detritiation of acetophenone as catalysed by a number of amines in these solvents. The ability of enzymes to catalyse many reactions under very mild conditions has prompted chemists to investigate whether they can design molecules that are just as effective. In the last chapter a preliminary investigation has been made to see how amines, when they are part of a macromolecular framework, perform as catalysts.

Biodiesel has come to the forefront of the energy community as a clean-burning, renewable energy that can replace the use of No. 2 Diesel fuel. Tall oil fatty acids, a by-product of the pulp and paper industry, may be utilized as a biodiesel feedstock. This thesis presents an empirical study of the acid-catalyzed esterification of tall oil fatty acids into biodiesel. Under atmospheric conditions, factorial design analysis determined the optimum parameters to be methanol ratio (6:1), sulfuric acid (5%), and temperature (60oC). This reaction was tolerant to water up to 1%. A pseudo-homogeneous second order kinetic model was applied to the reaction at the optimal conditions. The Activation Energy was calculated to be 19.73 kJ/mol with a pre-exponential factor of 23.6. Quality tests were performed under ASTM D 6751-06 to evaluate the final product with tall oil methyl esters having exceptional cold flow properties with a cloud point of -10.7oC.

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The selective manipulation of hydroxyl groups in di- and polyols is a frequently encountered problem in organic synthesis. Such processes are often tedious and/or moderate yielding, and often necessitate multistep protection / deprotection sequences. Applying boron–diol interactions previously exploited in molecular recognition and based on methods previously developed in our research group, we have developed two classes of chemical transformations: 1. Regioselective sulfonylations of carbohydrate derivatives catalyzed by a borinic ester, providing access to the corresponding mono-tosylates in high yields; 2. Selective monoalkylations and monosulfonylations of structurally diverse 1,2- and 1,3-diol substrates.

The selective manipulation of hydroxyl groups in di- and polyols is a frequently encountered problem in organic synthesis. Such processes are often tedious and/or moderate yielding, and often necessitate multistep protection / deprotection sequences. Applying boron–diol interactions previously exploited in molecular recognition and based on methods previously developed in our research group, we have developed two classes of chemical transformations: 1. Regioselective sulfonylations of carbohydrate derivatives catalyzed by a borinic ester, providing access to the corresponding mono-tosylates in high yields; 2. Selective monoalkylations and monosulfonylations of structurally diverse 1,2- and 1,3-diol substrates.

The first comprehensive account of Diels-Alder reactions occurring by a simultaneous self-assembly of the components and catalysis of the reaction via a Lewis Acid (LA) is presented in this study. The synthetic usefulness of the intramolecularity achieved by temporary connection of DA reaction components has been combined with the benefits of LA catalysis to overcome the regio- and stereochemical diversities associated with DA reactions of unsymmetrically substituted dienes and dienophiles. LA's employed in this study act both as temporary connectors (by binding to LB sites of the diene and dienophile) and as catalysts (by complexation to oxygen of carbonyl moieties of the dienophiles). Formation of the tether, cycloaddition; and removal of the transient linker all occurs in a single operation.* To illustrate the high selectivity accomplished in this approach, an experimental model system consisting of unsymmetrically substituted dienol 6 and methoxy diene 397 and an unsymmetrically substituted dienophile (methyl acrylate, MAC) was designed. Thermal combination of either of these two dienes with MAC produces nearly equimolar mixtures of all four possible adducts illustrating the unselective nature of the reactions. Use of LA's to mediate the reaction between dienol 6 and MAC results in exclusive regio- and stereoselective formation of a single adduct. In contrast, application of the same LA's for the reaction between the methoxy diene and MAC either results in the formation of two 'endo' regioisomers in low yield or no reaction at all.* Exclusive formation of a single adduct for the reactions of 6 is attributed to a process in which the LA both pre-organizes the reactants and catalyzes the cycloaddition. This phenomenon is not expected to be observed in the reactions of the methoxy diene. The difference in the behavior of the two dienes is ascribed to the difference in their interactions with the LA's. Dienol 6 is able to bind covalently and irreversibly to the LA's while methoxy diene 397 is only able to co-ordinate to the LA's in a reversible manner. Mechanistic studies strongly support the self-assembled pathway and exclude other potential routes. Reactions of dienol 6 with other structurally suitable dienophiles under similar LA mediated conditions exhibit higher selectivities and reactivities in comparison with their uncatalyzed counterparts. Use of a structurally similar chiral dienol induces a highly diastereoselective cycloadditions with different dienophiles, whereas the thermal versions of the reactions again produce all possible adducts. The strategy has also been used for DA reactions of ' 2H'-thiopyran dienols with dienophiles 'N'-acroyl-2-oxazolidinone (NAO), ('E')-3-[3-(methoxycarbonyl)propenoyl]-1,3-oxazolidin-2 -one (MCPO), and 'N'-phenylmaleimide (NPM). Use of MgII is demonstrated to be effective to stereoselectively catalyze reactions which are unselective thermally or do not proceed at all. *Please refer to dissertation for diagrams.

[EN] The present thesis focuses on the rationalization of the zeolite synthesis for catalysis by understanding the nature of active sites and their microenvironments, together with their influence on the mechanisms of catalyzed reactions. In the first part of the thesis, efforts have been put on attempting to achieve the regioselective locating of active sites in zeolite catalyst and, more specifically, on tunning acid site locations in zeolite framework. The development of a zeolite synthesis strategy and an indicator that can describe the aluminum distribution in the zeolite framework is important to evaluate if the final objective has been achieved. In this part, in order to evaluate aluminum distribution in MFI framework, an indicator based on monomolecular and bimolecular mechanisms of n-hexene catalytic cracking was proposed. First, several ZSM-5 samples were synthesized, which have been reported in the literature to have different aluminum distributions. These samples were characterized to be analogous in physicochemical properties and, then, tested in the n-hexene cracking to justify the usefulness of the indicator proposed in this work. Using 27Al MAS NMR, the aluminum locations were proved to be different, which was also reflected by the indicator in this thesis, justifying its applicability to evaluate aluminum locations. Afterward, this indicator has been employed to check the zeolite synthesis methodology that could potentially lead to different aluminum distribution in zeolite frameworks. Then, a boron-assisted synthesis is proposed considering that boron and aluminum may have competitive positioning in ZSM-5 framework. Then, and by means of DFT calculations, we have studied if the unit cell of MFI shows different stabilities when substituted by aluminum and/or boron in different T positions. It has been found that boron location is less favored when introduced in 10-ring channels of the MFI framework, while aluminum shows no preference for positioning among all the T-sites. ZSM-5 samples with different Si/Al and Si/B were synthesized and their physicochemical properties as well as the relative proportion of paired and isolated states of aluminum was characterized. Characterization includes n-hexene cracking, for which the samples showed different preference toward monomolecular and bimolecular reactions. Finally, once the materials were proved to have different aluminum distribution, they were employed in methanol-to-propene (MTP) reactions to show the influence of aluminum distribution on an industry-relevant reaction where the spatial confinement has an important impact. Indeed, the samples with aluminum preferentially positioned in 10-ring channel favored more monomolecular cracking and less bimolecular side reactions such as oligomerization and hydrogen transfer, giving higher propene yield and lower amount of alkanes and aromatics. The second part of the thesis focuses on rationalizing the synthesis of zeolites with cavities for catalyzing “a priory” selected reaction. More specifically, zeolite synthesis was carried out using OSDAs that mimic the transition state (TS) or a relevant intermediate in the target reaction. Ethylbenzene production by transalkylation between diethylbenzene and benzene was selected as the reaction to be catalyzed. A potential reaction TS was established and a diaryldimethylphosphonium OSDA was synthesized that mimicks the transition state in the diaryl-mediated mechanism of transalkylation between benzene and diethylbenzene. Then, the OSDA successfully led to the formation of the largepore zeolite ITQ-27. This ITQ-27 was tested in the reaction of transalkylation between benzene and diethylbenzene. The catalytic performance of this material was benchmarked to be superior than other commercially employed zeolites, such as USY, mordenite or Beta with similar physicochemical properties. Finally, Methanol to olefins (MTO) reaction was chosen as another target catalytic system, where the reaction pathways are more complicated than transalkylation between benzene and diethylbenzene but nevertheless they have been well established in the literature. Thus, several OSDAs were synthesized mimicking the intermediates and transition states of the paring pathway, which produces more propene and butenes, which are highly demanded among all products. The OSDAs led to formation of several cage-based small pore zeolites, such as CHA, RTH and AEI. All the zeolites obtained were tested in MTO reactions to evaluate their catalytic activity and gave high selectivity toward light olefins, which appeared to selectively depend on the zeolite tested. The tendency of each structure toward certain product distributions was related to the reaction mechanism by establishing a structure-reactivity correlation, when the experiment results were combined with theoretical calculations. It is proposed that different shape of the cavities stabilize different precursor intermediates present in the paring or side-chain pathways and this indicates the reaction preference between each pathway and therefore the product distributions. A linear correlation was obtained between the shape of cavities and the C3 = /C2 = molar ratios being possible. In this way, ITQ-3 (ITE structure) was predicted that should also give higher selectivity toward paring pathway, which has been demonstrated experimentally / [ES] La presente tesis se centra en la racionalización de la síntesis de zeolitas para su aplicación como catalizadores mediante la comprensión de la naturaleza de los sitios activos y sus microambientes, junto con su influencia en los mecanismos de las reacciones catalizadas. En la primera parte de la tesis, se han realizado esfuerzos para intentar lograr la ubicación regioselectiva de los sitios activos en el catalizador zeolítico y, más específicamente, en la ubicación controlada de sitios ácidos en la red cristalina de la zeolita. El desarrollo de una estrategia de síntesis adecuada junto con un indicador que pueda describir la distribución de aluminio en la red de la zeolita es importante para evaluar si se ha logrado el objetivo final. En esta parte, para evaluar la distribución de aluminio en la red de la zeolita MFI, se ha propuesto un indicador basado en los mecanismos monomoleculares y bimoleculares asociados a la reacción de craqueo catalítico de n-hexeno. En primer lugar, se sintetizaron varias muestras de ZSM-5, que según la literatura tienen diferentes distribuciones de aluminio. Estas muestras se caracterizaron por ser análogas en propiedades fisicoquímicas y, posteriormente, se analizaron en la reacción de craqueo de n-hexeno para justificar la utilidad del indicador propuesto en este trabajo. A partir de RMN MAS de 27Al se demostró que las ubicaciones de aluminio eran diferentes, lo que también se reflejó en el indicador propuesto en esta tesis, lo que justifica su aplicabilidad para evaluar distribuciones de aluminio. Posteriormente, este indicador se ha empleado para verificar la nueva metodología de síntesis de zeolitas que podría conducir a una distribución de aluminio diferente en sus estructuras cristalinas. En este sentido, se propone la síntesis de la zeolita ZSM-5 asistida por boro, considerando que el boro y el aluminio podrían tener un posicionamiento competitivo en la estructura MFI. Mediante cálculos de DFT, se ha estudiado si la celda unidad de MFI muestra diferente estabilidad cuando se introduce aluminio y/o boro en diferentes posiciones cristalográficas T. Se ha encontrado que la ubicación del boro está menos favorecida cuando se introduce en los canales de 10 miembros de la estructura MFI, mientras que el aluminio no muestra preferencia por el posicionamiento entre todos los sitios T. Se sintetizaron muestras de ZSM-5 con diferentes Si/Al y Si/B y se caracterizaron sus propiedades fisicoquímicas, así como la proporción relativa de estados emparejados y aislados de aluminio. La caracterización incluye el craqueo de n-hexeno, para el cual las muestras mostraron una preferencia diferente hacia las reacciones monomoleculares y bimoleculares. Finalmente, una vez demostrada la distinta distribución de aluminio en los materiales sintetizados, estos catalizadores se estudiaron en la reaccióde metanol a propeno (MTP) para mostrar la influencia de la distribución de aluminio en una reacción relevante a nivel industrial, donde el confinamiento espacial tiene un impacto importante. De hecho, las muestras con aluminio posicionadas preferentemente en un canal de 10 miembros favorecen reacciones de craqueo monomolecular frente a reacciones secundarias bimoleculares, como por ejemplo reacciones de oligomerización y de transferencia de hidrógeno, dando un mayor rendimiento a propeno y una menor cantidad de alcanos y compuestos aromáticos. La segunda parte de la tesis se centra en racionalizar la síntesis de zeolitas con cavidades para catalizar una reacción seleccionada "a priori". Más específicamente, la síntesis de zeolita se llevó a cabo utilizando agentes directores de estructura orgánicos (ADEO) que mimetizan el estado de transición (ET) o el intermedio relevante en la reacción objetivo. La producción de etilbenceno por transalquilación entre dietilbenceno y benceno se ha seleccionado como una reacción objetivo a catalizar. Se estableció el ET determinante de la reacción y se sintetizó un ADEO tipo diarildimetilfosfonio que mimetiza el estado de transición del mecanismo de la reacción de transalquilación entre benceno y dietilbenceno. Dicho ADEO permitió la cristalización de la zeolita de poro grande ITQ-27, cuyo comportamiento catalítico se estudió en la reacción de transalquilación entre benceno y dietilbenceno. La actividad catalítica de la zeolita ITQ-27 se mostró claramente superior al de otras zeolitas empleadas comercialmente, como USY, mordenita o Beta, todas ellas con propiedades fisicoquímicas similares a la ITQ-27. Finalmente, la reacción de metanol a olefinas (MTO) se eligió como otro sistema catalítico objetivo, donde los mecanismos de reacción son mucho más complicados que en el caso de la reacción de transalquilación entre benceno y dietilbenceno, pero, sin embargo, están bien establecidos en la literatura. Se sintetizaron varios ADEOs que mimetizan los intermedios y los estados de transición de la ruta “paring”, que produce más propeno y butenos, y que son posiblemente los productos más demandados. Dichos ADEOs mímicos permitieron la formación de varias zeolitas de poro pequeño basadas en cavidades, como las zeolitas CHA, RTH y AEI. Todas las zeolitas obtenidas se probaron en la reacción MTO para evaluar su actividad catalítica, obteniéndose una alta selectividad hacia distintas olefinas ligeras, cuya selectividad depende de la forma y tamaño de la cavidad de cada zeolita. La tendencia de cada estructura hacia ciertas distribuciones de productos se ha relacionado con el mecanismo de reacción, pudiendo establecer una correlación estructura-reactividad al combinar los resultados experimentales con cálculos teóricos. / [CA] La present tesi es centra en la racionalització de la síntesi de zeolites per a la seva aplicació com a catalitzadors mitjançant la comprensió de la naturalesa dels centres actius i els seus microambientes, juntament amb la seva influència en els mecanismes de les reaccions catalitzades. A la primera part de la tesi, s'han realitzat esforços per intentar aconseguir la ubicació regioselectiva dels centres actius en el catalitzador zeolític i, més específicament, en la ubicació controlada de centres àcids en la xarxa cristal·lina de la zeolita. El desenvolupament d'una estratègia de síntesi adequada juntament amb un indicador que descriga la distribució d'alumini a la xarxa de la zeolita és important per avaluar si s'ha aconseguit l'objectiu final. En aquesta part, per avaluar la distribució d'alumini a la xarxa de la zeolita MFI, s'ha proposat un indicador basat en els mecanismes monomoleculares i bimoleculars associats a la reacció de craqueig catalític de n-hexé. En primer lloc, es van sintetitzar diverses mostres de ZSM-5, que segons la literatura tenen diferents distribucions d'alumini. Aquestes mostres es van caracteritzar per ser anàlogues en propietats fisicoquímiques i, posteriorment, es van analitzar en la reacció de craqueig de nhexéper justificar la utilitat de l'indicador proposat en aquest treball. A partir dels espectres de RMN MAS de 27Al es va demostrar que les ubicacions d'alumini eren diferents, el que també es va reflectir en l'indicador proposat en aquesta tesi, justificant la seva aplicabilitat per avaluar distintes distribucions d'alumini. Posteriorment, aquest indicador s'ha emprat per verificar la nova metodologia de síntesi de zeolites que podria conduir a una distribució d'alumini diferent al llarg de les seves estructures cristal·lines. En aquest sentit, s’ha proposat la síntesi de la zeolita ZSM-5 assistida per bor, considerant que el bor i l'alumini podrien tenir un posicionament competitiu en l'estructura MFI. Mitjançant càlculs de DFT, s'ha estudiat si la cel·la unitat de MFI mostra diferent estabilitat quan s’introdueix alumini i/o bor en diferents posicions cristal·logràfiques T. S'ha trobat que la ubicació dels àtoms de bor està menys afavorida als canals de 10 membres de la estructura MFI, mentre que l'alumini no mostra preferència pel posicionament entre tots els llocs T. Es van sintetitzar mostres de ZSM-5 amb diferents relacions de Si/Al i Si/B i es van caracteritzar les seves propietats fisicoquímiques, així com la proporció relativa d'estats aparellats i aïllats d'alumini. La caracterització inclou la reacció de craqueig de n-hexé, on les mostres van mostrar una preferència diferent cap a les reaccions monomoleculares i bimoleculars. Finalment, un cop demostrada la diferent distribució d'alumini en els materials sintetitzats, aquests catalitzadors es van estudiar a la reacció de metanol a propè (MTP) per mostrar la influència de la distribució d'alumini en una reacció rellevant a nivell industrial, on el confinament espacial té un impacte important. De fet, les mostres amb alumini posicionades preferentment en un canal de 10 membres afavoreixen reaccions de craqueig monomolecular enfront de reaccions secundàries bimoleculars, com ara reaccions d'oligomerització i de transferència d'hidrogen, donant un major rendiment a propè i una menor quantitat d'alcans i compostos aromàtics. La segona part de la tesi es centra en racionalitzar la síntesi de zeolites amb cavitats per catalitzar una reacció seleccionada "a priori". Més específicament, la síntesi de zeolita es va dur a terme utilitzant agents directors d'estructura orgànics (ADEO) que mimetitzen l'estat de transició (ET) o l'intermedi rellevant en la reacció objectiu. La producció de etilbenzèper transalquilació entre dietilbenzè i benzè s'ha seleccionat com una reacció objectiu a catalitzar. Es va establir l'ET determinant de la reacció i es va sintetitzar un ADEO tipus diarildimetilfosfoni que mimetitza eixe estat de transició. Eixe ADEO va permetre la cristal·lització de la zeolita de porus gran ITQ-27, i el seu comportament catalític es va estudiar en la reacció de transalquilación entre benzè i dietilbenzè. L'activitat catalítica de la zeolita ITQ-27 es va mostrar clarament superior a la d'altres zeolites emprades comercialment, com la USY, mordenita o Beta, totes elles amb propietats fisicoquímiques similars a la ITQ-27. Finalment, la reacció de metanol a olefines (MTO) es va triar com un altre sistema catalític objectiu, on els mecanismes de reacció són molt més complicats que en el cas de la reacció de transalquilació entre benzè i dietilbenzè, però que, al mateix temps, estan ben establerts en la literatura. Es van sintetitzar diversos ADEOs que mimetitzen alguns dels intermedis i dels estats de transició de la ruta "paring", que produeix més propè i butens, i que són possiblement els productes més demandats. Aquests ADEOs mímics van permetre la formació de diverses zeolites de porus petit basades en cavitats, com les zeolites CHA, RTH i AEI. Totes les zeolites obtingudes es van provar en la reacció MTO per avaluar la seva activitat catalítica, obtenint una alta selectivitat cap a diferents olefines lleugeres, on la selectivitat cap a cada olefina lleugera depèn de la forma i mida de la cavitat de cada zeolita. La tendència de cada estructura cap a certes distribucions de productes s'ha relacionat amb el mecanisme de reacció, i s´ha pogut establir una correlació estructura-reactivitat al combinar els resultats experimentals amb càlculs teòrics. / Li, C. (2020). Rationalize the synthesis of zeolite catalysts by understanding reaction mechanism [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/147115

The Bucherer-Bergs reaction is a classical multi-component reaction that yields hydantoins, which can be hydrolysed to afford α-amino acids. Hydantoins have many uses in modern organic synthesis, and this moiety has been included in a number of therapeutic agents, which have a wide range of biological activities. Herein, we report a mild synthesis of 5- and 5,5-substituted hydantoins from α-aminonitriles using Hünig’s base and carbon dioxide. This reaction can be performed in excellent yields, using a variety of organic solvents and is applicable to a range of substrates. In an extension to the above methodology, a one-pot Lewis acid-catalysed synthesis of hydantoins from ketones has also been developed and optimised in organic media. This reaction can be performed in excellent yields and is suitable for the synthesis of 5- and 5,5-substituted hydantoins.