Controlled Microwave Heating in Modern Organic Synthesis

Kappe, C. Oliver

doi:10.1002/anie.200400655

Cited by 3,338 publications

(1,709 citation statements)

References 433 publications

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“…Tiene un rango de frecuencia desde 300 MHz a 300 GHz y la correspondiente longitud de onda de 1 m a 1 mm. La frecuencia más usada a nivel industrial y doméstico es la 2.45 GHz [15,16] .…”

Section: Influencia De Las Mw En La Obtención De Poli(dl áCido Lácticunclassified

Síntesis de poli ácido láctico y poli ricinoleato empleando calentamiento por microondas y su utilización en la producción de termoplasticos de poliuretano

2011

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Resumen: En este trabajo se realiza la síntesis de poliuretano termoplástico (TPU) utilizando oligómeros sintetizados a partir de ácido DL Láctico y ácido ricinoléico. Estos polioles fueron obtenidos desde fuentes renovables, mediante la policondensación de los monómeros sin catalizador. Se evalúo el efecto de las microondas en las reacciones, donde se encuentraron efectos no térmicos que disminuyen la energía de activación y aumentan la constante de velocidad, en una cinética de tercer orden; el seguimiento y la caracterización de los productos intermedios se realiza mediante la cuantificación de valor ácido por titulación (ASTM D4662 -03) y número de hidroxilos (ASTM D4274 -05). Los termoplásticos obtenidos se caracterizan mediante las siguientes pruebas: resistencia tensil y % elongación (ASTM D882-97), análisis de calorimetría diferencial de barrido (DSC), espectroscopía infrarroja (IR) y microscopía de fuerza atómica (AFM). Los TPU se obtuvieron con un porcentaje de segmentos suaves del 50%, todos presentan morfología segmentada y segregación de fases. Las formulaciones con poli(DL ácido Láctico) y Difenilmetanodiisocianato (MDI) presentan la mayor rigidez y temperatura de transición vítrea (Tg). Palabras-claves: Poliuretano termoplástico, poli(DL ácido Láctico), poliricinoleato. Synthesis of Poly Lactic Acid and Poly Ricinoleate Using Microwave Heating and Their Use in the Production of Polyurethane ThermoplasticAbstract: In this paper we report on the synthesis of thermoplastic polyurethane (TPU) using oligomers synthesized from DL Lactic acid and ricinoleic acid. These polyols were obtained from renewable sources by polycondensation of monomers without catalysts. The effect of microwaves on the reactions was evaluated, where non-thermal effects were found to lower the activation energy and increase the rate constant in a third-order kinetics. The monitoring and characterization of intermediate products was done by quantification of acid value by titration (ASTM D4662 -03) and hydroxyl number (ASTM D4274 -05). Thermoplastics obtained are characterized by the following tests: tensile strength and elongation percentage (ASTM D882-97), analysis of differential scanning calorimetry (DSC), infrared spectroscopy (IR) and atomic force microscopy (AFM). TPU was obtained with a percentage of 50% soft segments, all have segmented morphology and segregation of phases. The formulations with poly(DL lactic acid) and Methylene diphenyl diisocyanate (MDI) have the highest stiffness and glass transition temperature (Tg). Keywords: Thermoplastic polyurethane, poly(DL lactic acid), polyricinoleate. IntroducciónLa utilización de productos naturales como aceites vegetales y grasas ha atraído la atención de científicos y de la industria en los últimos años, debido a consideraciones ambientales. Estas materias primas son sostenibles, renovables, y lo más importante, biodegradables. En los aceites vegetales se han realizado modificaciones químicas en los grupos éster y dobles enlaces, para obtener una amplia gama de biopolímero...

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“…Tiene un rango de frecuencia desde 300 MHz a 300 GHz y la correspondiente longitud de onda de 1 m a 1 mm. La frecuencia más usada a nivel industrial y doméstico es la 2.45 GHz [15,16] .…”

Section: Influencia De Las Mw En La Obtención De Poli(dl áCido Lácticunclassified

Síntesis de poli ácido láctico y poli ricinoleato empleando calentamiento por microondas y su utilización en la producción de termoplasticos de poliuretano

2011

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“…[9] Despite these advances, the N-alkylation of amines with alcohols under microwave irradiation remains less unexplored. [10] We have reported iridium-catalyzed synthesis of dialkylated ureas from ureas and alcohols.…”

Section: Introductionmentioning

confidence: 99%

Microwave-Assisted Efficient Synthesis of Dialkylated Ureas from Ureas

Li¹,

Ma²

2015

Proceedings of the 2015 International Conference on Education, Management, Information and Medicine

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Abstract. Microwave irradiation provided an effective tool for rapid, clean, and high-yielding transformations of organic reactions. Despite these advances, the N-alkylation of amines with alcohols under microwave irradiation remains less unexplored. We demonstrated a general and efficient method for the synthesis of dialkylated ureas from ureas under microwave irradiation is described. Reactios of ureas with a series of alcohols, such as benzyl alcohol, benzylic alcohols bearing a electron-donating group or a electron-withdrawing group, afforded the desired dialkylated ureas with good yields at a short time. Experimental results exhibited obvious advantages of microwave irradiation.

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“…[30][31][32] MW energy at the common frequency of 2.45 GHz (0.0016 eV) is too low to break chemical bonds and is also lower than the energy of Brownian motion. [33] Therefore, MW cannot induce, but can enhance chemical reactions. [34] MW-enhanced chemistry is based on the efficient heat transfer achieved by dielectric heating.…”

Section: Introductionmentioning

confidence: 99%

“…This phenomenon is dependent on the ability of a specific material (solvent or reagent) to absorb MW energy and convert it into heat. [33] In contract to conductive heating, MW irradiation causes volumetric heating via the direct coupling of the electromagnetic field with molecules (solvents, reagents, catalysts) in the reaction mixture (minimized or no wall effect). As a result, fast selective heating can be attained by irradiating polar materials in a MW field.…”

Section: Introductionmentioning

confidence: 99%