Aproximación electroquímica a la reacción de substitución nucleófila aromática : determinación del mecanismo de oxidación de los [sigma]-complejos : comportamiento electroquímico de compuestos nitroaromáticos /

Consultable des del TDXTítol obtingut de la portada digitalitzadaEn la presente tesis doctoral se recoge por primera vez el estudio electroquímico de la reacción de substitución nucleófila aromática vía oxidación electroquímica del complejos intermedios,s-complejos (o complejos de Meisenheimer), ya sea mediante proceso de tipo NASH (substitución de hidrógeno) o de tipo NASX (substitución de heteroátomo)1-2. Los estudios electroquímicos fueron realizados utilizando voltametría cíclica (CV) para los estudios mecanísticos, mientras que los estudios preparativos se realizaron mediante electrólisis a potencial controlado. Un amplio número de nucleófilos han sido utilizados (H-, CN-, F-, -OR, -SR, RNH2, RCONH2, BuLi, BuMgCl). Mediante la realización de experimentos de voltametría cíclica (CV) se ha podido detectar y caracterizar todo tipo de s-complejos (sH y sX-complejos) y se ha podido determinar el mecanismo de oxidación de los mismos (esquema 1). En referencia a los estudios electrosintéticos realizados3, es destacable la preparación de alquilaminas y amidas vía substitución nucleófila aromática de hidrógeno por medio de oxidación electroquímica (proceso NASH)4. El proceso descrito muestra la obtención de buenos rendimientos (15-85%) en lo que es un proceso simple, directo,altamente regioselectivo y respetuoso con el medioambiente. En este sentido se han realizado extensiones del presente método de síntesis, para la obtención de cetonas aromáticas a partir de la reacción de substitución nucleófila aromática de hidrógeno oxidada electroquímicamente5. Los rendimientos obtenidos fueron altos (80-100%), siendo en la mayoría de los casos procesos altamente quimio- y regioselectivos. La última aproximación electroquímica para la reacción de substitución nucleófila aromática recogida en la presente Tesis Doctoral es la síntesis del alquilnitroderivados aromáticos, para ello se utilizó butililio y cloruro de butilmagnesio como nucleófilos. Asimismo hay que decir que en la presente Tesis Doctoral, se describe el comportamiento electroquímico mostrado por diferentes compuestos nitroaromáticos. Estos compuestos mono-, di- y trinitroderivados aromáticos son reactivos comúnmente utilizados al realizar reacciones de substitución nucleófila aromática. Los estudios mecanísticos realizados mediante VC, han permitido clasificar el comportamiento electroquímico de los compuestos nitroaromáticos en cuatro grupos6-7 en función de la velocidad de barrido de potencial (v).The nucleophilic aromatic substitution through electrochemical oxidation of the intermediate s-complexes (Meisenheimer complexes), in terms of NASH process (substitution of hydrogen) and NASX process (substitution of heteroatom) through electrochemical oxidation of the intermediate sH-complexes and/or sX-complexes, respectively is reported in this Thesis for the first time1-2 in simple nitroaromatic compounds. The studies have been carried out by means of cyclic voltammetry (CV) and preparative electrolysis using a wide list of nucleophiles (H-, CN-, F-, -OR, -SR, RNH2, RCONH2, BuLi, BuMgCl). The cyclic voltammetry (CV) experiments allow for the detection and characterization of the s-complexes (sH- and sX-complexes) and led us to a proposal for the mechanism of the oxidation step (Scheme 1). In terms of electro-synthetic studies3, alkylamines and amides are readily prepared by nucleophilic aromatic substitution of hydrogen in nitroarenes by electrochemical oxidation (NASH process)4. Useful yields (15-85%) are achieved in a simple direct, regioselective and environmental favourable amination process. In addition, nitroaromatic ketones are readily prepared by nucleophilic aromatic substitution of hydrogen in nitroarenes by electrochemical oxidation (NASH process)5. Useful yields are achieved (80-100%), in which represents an environmentally favourable route for obtaining nitroaromatic ketones. The last electrochemical approach investigated is the synthesis of alkylnitroaromatic compounds. Alkylnitroaromatic compounds are readily prepared via nucleophilic aromatic substitution for hydrogen or heteroatom by electrochemical oxidation of the s-complex using Butyllithium and butylmagnesium chloride as nucleophiles. The electrochemical behaviour of nitroaromatic compounds is also reported in the present thesis. Note that the most part of the aromatic reactants in the nucleophilic aromatic substitution reaction are mainly mono-, di- and trinitroaromatic compounds. After exhaustive electrochemical mechanistic studies carried out in this thesis by means of CV, we are capable of classified in terms of v (scan rate)the electrochemical behaviour of the nitroaromatic compounds in four groups 6-7

Electrochemical incorporation of carbon dioxide into fluorotoluene derivatives under mild conditions

One of the main challenges to combat climate change is to eliminate or reuse Carbon dioxide (CO), the largest contributor to the greenhouse gases that cause global warming. It is also important to synthesize compounds through greener technologies in order to obtain more environmentally friendly solutions. This study describes the electrocarboxylation process of α,α,α-trifluorotoluene using different working electrodes (glassy carbon, silver and copper) and electrolytes (polar aprotic solvent and ionic liquid). Carboxylated compounds were obtained in the same way in both electrolytic medias with more than 80% conversion rates, high yields, good selectivity, and moderate efficiencies using silver and copper as cathodes in organic electrolytes and ionic liquids

Use of CO2 for electrosynthesis

Altres ajuts: acords transformatius de la UABA review of the main ideas related to the capture and valorization of CO by using electrochemical processes is presented. The advantages of using an electrode-controlled potential that provides the possibility of reducing CO to non-fossil carbon-based fuels, or of using this atmospheric pollutant in organic synthesis processes that rely on electrocarboxylation steps are outlined. The implications of a reduction in atmospheric CO emissions in the global climate change emergency, while at the same time finding alternative and clean ways of producing valuable fuels and chemicals, are emphasized. Particular attention is paid to the powerful role that ionic liquids can play as ideal solvents and electrolytes in such electrochemical reactions. A general description of the advantages that these liquids have for the solubilization and the support of the electrochemical reduction of CO is presented

Sustainable and efficient electrosynthesis of naproxen using carbon dioxide and ionic liquids

The use of CO2 as a C1 carbon source for synthesis is raising increasing attention both as a strategy to bring value to carbon dioxide capture technologies and a sustainable approach towards chemicals and energy. The presented results focus on the application of electrochemical methods to incorporate CO2 into organic compounds using ionic liquids as electrolytes, which provides a green alternative to the formation of C-C bonds. In this sense, the current manuscript shows that Naproxen (6-Methoxy-α-methyl-2-naphthaleneacetic acid) can be synthetizing in high yield (89%) and conversion rates (90%) through an electrocarboxylation process using CO2 and ionic liquids. The role of the cathode and solvent, which can potentially enhance the synthesis, is also discussed. The "green" route described in the current work would open a new sustainable strategy for the electrochemical production of pharmaceutical compounds

Electrochemical Reduction of 4-Nitrobenzyl Phenyl Thioether for Activation and Capture of CO2

Altres ajuts: Acord transformatiu CRUE-CSICIn this work, a new simple molecule, 4-nitrobenzyl phenyl thioether (1), is prepared and used for controlling and tuning CO reactivity in function of the electrode potential. The first part of the study is devoted to determining the electrochemical reduction mechanism of 1 in N,N-dimethylformamide under nitrogen. The compound shows a first reversible one-electron transfer process, whereas the reaction cleavage of the C−S bond takes place after a second electron transfer process through a stepwise mechanism (thermodynamic and kinetic parameters are conveniently determined). In the second part of the study, the inert atmosphere was replaced by a CO atmosphere. At low potential values, compound 1 acts as a redox mediator that allows the reduction of CO at ca. −1.2 V vs. SCE. The electrochemical generation of 1 at more negative potential values leads to a C−S bond cleavage reaction that yields the corresponding nitrobenzyl and thiosulfate anions, which react with CO. The nitro aromatic anion derivative makes it possible to obtain electrocarboxylated derivatives, whereas the thiophenolate anion captures CO reversibly. Hence, this research opens a new way of tuning and controlling the reaction processes associated with CO from homogenous catalysis at low negative potentials, to electrocarboxylation processes passing to CO reversible electrochemically triggered adsorption processes

Solid Multiresponsive Materials Based on Nitrospiropyran-Doped Ionogels

Altres ajuts: acords transformatius de la UABThe application of molecular switches for the fabrication of multistimuli-responsive chromic materials and devices still remains a challenge because of the restrictions imposed by the supporting solid matrices where these compounds must be incorporated: they often critically affect the chromic response as well as limit the type and nature of external stimuli that can be applied. In this work, we propose the use of ionogels to overcome these constraints, as they provide a soft, fluidic, transparent, thermally stable, and ionic-conductive environment where molecular switches preserve their solution-like properties and can be exposed to a number of different stimuli. By exploiting this strategy, we herein pioneer the preparation of nitrospiropyran-based materials using a single solid platform that exhibit optimal photo-, halo-, thermo-, and electrochromic switching behaviors

Electroinduced crosslinking of triphenylamine-based polybenzoxazines

Altres ajuts: acord transformatiu CRUE-CSICPolybenzoxazines attract much attention as good phenolic resins due to their interesting and useful properties. Recently, benzoxazine monomers have been employed as crosslinking agents to enhance the properties of different types of polymers by being used as additives to a secondary cure process. In this paper, we propose a new electroinduced approach to increase the crosslinking density of electroactive polybenzoxazines through the design of new monomers that contain triphenylamine groups as electrodimerization points. The use of electrochemical techniques means the crosslinking process can be monitored and also the electrochemical reaction process upon polybenzoxazine oxidation either in solution or ionogel matrixes can be disclosed. These studies lay the foundations for the design of smart polybenzoxazines that could undergo dual-cure mechanisms at low electrochemical potential values

Solid Multiresponsive Materials Based on Nitrospiropyran-Doped Ionogels

Altres ajuts: Acord transformatiu CRUE-CSICThe application of molecular switches for the fabrication of multistimuli-responsive chromic materials and devices still remains a challenge because of the restrictions imposed by the supporting solid matrices where these compounds must be incorporated: they often critically affect the chromic response as well as limit the type and nature of external stimuli that can be applied. In this work, we propose the use of ionogels to overcome these constraints, as they provide a soft, fluidic, transparent, thermally stable, and ionic-conductive environment where molecular switches preserve their solution-like properties and can be exposed to a number of different stimuli. By exploiting this strategy, we herein pioneer the preparation of nitrospiropyran-based materials using a single solid platform that exhibit optimal photo-, halo-, thermo-, and electrochromic switching behaviors

Dual-Wavelength Gated oxo-Diels-Alder Photoligation

Altres ajuts: Acord transformatiu CRUE-CSICThe control of chemical functionalization with orthogonal light stimuli paves the way toward manipulating materials with unprecedented spatiotemporal resolution. To reach this goal, we herein introduce a photochemical reaction system that enables two-color control of covalent ligation via an oxo-Diels-Alder cycloaddition between two separate light-responsive molecular entities: a UV-activated photocaged diene based on ortho-quinodimethanes and a carbonyl dienophile appended to a diarylethene photoswitch, whose reactivity can be modulated upon illumination with UV and visible light

Electrocarboxylation of Spiropyran Switches through Carbon-Bromide Bond Cleavage Reaction

Acord transformatiu CRUE-CSICAltres ajuts: Autonomous University of Barcelona predoctoral PIF grantThis manuscript deals with carbon capture and utilization to synthetize high-added chemicals using CO as a C1-organic building block for C−C bond formation. The study focuses on the electrocarboxylation of 1,3,3-trimethylindolino-6'-bromobenzopyrylospiran switch (Br-BIPS). Prior to the electrocarboxylation process, the electrochemical reduction mechanism of Br-BIPS and CO is disclosed in polar aprotic solvents using two different cathodes (glassy carbon and silver) under nitrogen atmosphere. Once the role of the cathode in the reduction carbon-bromide bond cleavage is understood, carboxylated spiropyran derivatives can be synthesized in moderate yields and conversion rates through an electrocarboxylation process using CO silver cathode and polar aprotic solvents. The "green" efficient route described in the current work would open a new sustainable strategy for designing and building "smart" surfaces with switchable physical properties