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SILANE, (CH3)2Sicl2 Naturaleza y Tecnología Enero-Mayo 2021 ISSN 2007-672X Universidad de Guanajuato DISCOVERY OF METHYLCHLOROSILYLENE (CH SiCl:) AS A KEY 3 INTERMEDIATE IN THE DIRECT SYNTHESIS OF DIMETHYLDICHLORO- SILANE, (CH3)2SiCl2 Kenrick M. Lewis, Momentive Performance Materials, 771 Old Sawmill River Rd., Tarrytown, NY 10591. Preambulo sólido-gas catalizada por cobre. El Me2SiCl2 era conocido con anterioridad En uno de los números recientes de la desde antes de la Segunda Guerra revista Organometallics (2021, 40, 459- Mundial, sin embargo, su síntesis, se 462) en la que se incluye una sección basaba en una reacción de metátesis entre dedicada a personalidades pioneras en la tetracloruro de silicio (SiCl4) y un reactivo química organometálica y cuyas de Grignard, por ejemplo, MeMgBr. Se investigaciones han tenido gran influencia conocía que su hidrólisis permitía obtener en el campo industrial, se hace referencia el poli(dimetilsiloxano), por lo que al Dr. Kenrick M. Lewis, cuyos trabajos resultaba muy conveniente y atractiva su son reconocidos al impactar en aspectos síntesis debido a su estabilidad térmica y a fundamentales de la química de muchas aplicaciones que potencialmente organosilanos, entre ellos, la famosa se podrían desarrollar en aislantes para reacción directa de producción de motores eléctricos, radios de vuelo y diclorodimetilsilano (Me2SiCl2), muchas más, motivado a la vez por la compuesto químico esencial para la necesidad de materiales con aplicaciones industria moderna de los polímeros de militares. Sin embargo, la reacción no era silicio. En este número de la revista factible de ser escalada o trasladada a una Naturaleza y Tecnología, el Dr. Lewis producción industrial, lo que llevó a que el generosamente comparte los detalles que profesor Eugene Rochow en General condujeron al descubrimiento de una Electric, y durante la Segunda Guerra, especie química intermediaria clave en el descubriera que la reacción directa entre proceso de síntesis del referido compuesto silicio y cloruro de metilo en fase gas, y que en años recientes publicó, luego de catalizada por cobre, generaba qué durante un buen tiempo al ser parte de principalmente el compuesto deseado. un secreto industrial, la información estuvo reservada. 2CH3Cl(g) + Si(s) → (CH3)2SiCl2(l) (1) Con el propósito de obtener una mejor La referencia que se hace en el número de comprensión de la descripción que el Dr. Organometallics arriba citado, menciona Lewis presenta en este artículo de que el resultado de la reacción fue divulgación, conviene hacer referencia a la publicado por Rochow en un artículo de 3 reacción química involucrada, llamada páginas (The Direct Synthesis of Síntesis Directa o Proceso Directo, y que Organosilicon Compounds, J. Am. Chem. se clasifica como una adición oxidante Soc. 1945, 67, 963−965), que no 17 Naturaleza y Tecnología Enero-Mayo 2021 ISSN 2007-672X Universidad de Guanajuato importando lo breve, se considera como Key words: methylchlorosilylene, Direct uno de los artículos más importantes en la Synthesis, Rochow-Müller, química orgánica de silicio por el impacto dimethyldichlorosilane que a lo largo de los años ha tenido en la industria química. Años después se conoció y se reconoció, que por los Resumen mismos años (1945) Richard Müller en Alemania, había trabajado de igual manera El propósito en esta memoria es dar a en la misma reacción, por lo que el proceso conocer, las etapas y eventos que dieron es llamado también la Síntesis Directa lugar al descubrimiento de la especie Rochow-Müller (Müller publicó su metilclorosilileno (sililenoid) como un experiencia en One hundred years of intermediario clave en la Síntesis Directa organosilicon chemistry. J. Chem. Educ. Rochow-Müller. De manera particular, 1965, 42, 41). El primer experimento deseo discutir la influencia de distintos exitoso de Rochow generó 5 mL de factores y situaciones específicas que dieron lugar al descubrimiento, y a la vez Me2SiCl2, cantidad obviamente difícil de considerar viable como un producto para pagar tributo a mis guías, a mis consejeros y a mis colaboradores. dar lugar a tantas aplicaciones. Sin embargo, luego de investigaciones y Palabras clave: metilclorosilileno, Síntesis desarrollos tecnológicos en los que se Directa Rochow-Múller, involucraron diseño de reactores de lecho diclorodimetilsilano fluidizado, de haber optimizado el empleo del catalizador de cobre, se sabe que en la When, in January 1979, I transferred from actualidad se producen algo así como 1.4 the Linde Research Department of Union millones de toneladas métricas anualmente Carbide to the Exploratory and Basic de esta molécula que ha sido pieza clave Group of Silicones R&D, one of my first en la industria química moderna de los assignments was to identify and develop polímeros de silicio. exploitable concepts and phenomena to improve the performance of the Rochow- Müller Direct Synthesis of methylchlorosilanes. Dr. Bernie Kanner, Abstract my Group Manager, had told me that there My intention, in this memoir, is to was much that was still unknown about the document the events leading to discovery reaction, despite almost forty years of of methylchlorosilylene (silylenoid) as a commercial practice at that point. I was key intermediate in the Rochow-Müller excited by the fact the Direct Synthesis is Direct Synthesis of a copper-catalyzed reaction. My dimethyldichlorosilane. In particular, I fascination with copper chemistry had want to discuss the influence of various started during my senior year at the factors and individuals and pay tribute to University of Alberta (Edmonton) with a mentors and contributors. lecture by Prof. Robert Jordan on the physiological role of copper enzymes and 18 Naturaleza y Tecnología Enero-Mayo 2021 ISSN 2007-672X Universidad de Guanajuato copper proteins. It continued through 4. Promoters, particularly zinc, cadmium graduate school at the University of and antimony, enhance catalytic activity Massachusetts (Amherst), where I had and selectivity when used in small (< 1 studied the corrosion chemistry of the weight percent) amounts. copper intrauterine device (IUD) during 5. Neither methyl chloride adsorption nor my doctoral research. In the Linde copper diffusion is the rate-limiting step of Research Department, use of chelation the reaction. technology to recover copper and other metals from industrial wastes and 6. Methyl chloride is dissociatively hydrometallurgical solutions was one of chemisorbed on the catalytic surface. my projects. Now, in Silicones R&D, I was going to study the catalysis of the 7. The reaction follows Langmuir- Direct Synthesis with emphasis on the role Hinshelwood kinetics. of copper. 8. (CH3)2SiCl2 is formed from a surface My review of the published literature had intermediate with dimethylsilyl groups. revealed that the role of copper in the At the conclusion of his Plenary Lecture at catalysis had not been elucidated. the International Symposium on Prevailing ideas about the mechanism of Organosilicon Chemistry in 1969, Bazant the Rochow-Müller Direct Synthesis of acknowledged the difficulty of dimethyldichlorosilane had originated mechanistic research on a reaction as from the research of Voorhoeve and complex as the Rochow-Müller Direct coworkers, and van den Berg and Synthesis of methylchlorosilanes (see coworkers in The Netherlands, Bazant and Pure & Applied Chem., 19(1969) 473 – coworkers in Czechoslovakia and from 488). This is a copper-catalyzed, gas – Golubtsov, Lobusevich and coworkers in solid reaction, not the familiar reaction of the USSR. Voorhoeve’s monograph, gaseous reactants over a heterogeneous Organohalosilanes: Precursors to catalyst. Bazant’s remarks inspired the Silicones, was the primary authoritative surface-chemical investigations, which we source of published information. The initiated in 1980. Our objectives were: tenets of the prevailing hypothesis were: • To understand the significance of 1. Cu3Si (η phase) is the active catalyst bonding, thermochemical and leading to selective formation of morphological changes accompanying (CH3)2SiCl2. alloy formation in the Cu-Si binary and 2. The polarity of the metal – silicon bond Cu-Si-Zn ternary systems. in metal silicides determines or influences • To determine surface compositions in product selectivity. these systems in the temperature range 3. The Cu – Si bond energy (46 kcal/mole) (280° – 350°C) in which selectivity to is greater than the Si – Si bond energy (42 dimethyldichlorosilane is high. kcal/mole). 19 Naturaleza y Tecnología Enero-Mayo 2021 ISSN 2007-672X Universidad de Guanajuato • To characterize the valence states of Cu, retained. The Boulder team showed that Zn and Si in these systems in vacuo and silicon surface enrichment was predicted following methyl chloride chemisorption. by the empirical rule of Burton and Machlin. Their results were published in • To elucidate structure and composition of Applied Surface Science, 14(1982 – 83) the surface intermediates and active sites 359. We showed that the thermodynamics following chemisorption. of silicon enrichment was in agreement • To assess state-of-the-art mechanistic with the comprehensive model of proposals and make new ones consistent Wynblatt and Ku, but it was 1987 before with the surface analytical results. we were permitted to publish our results (Catalysis 1987, J. W. Ward, Editor, pp • To exploit findings that will improve the 415 – 434). performance of our commercial reactors. In the meantime, we had calculated the Although our research was begun Cu-Si bond energy to be 30.6 ± 2.4 independently, it soon became a joint kcal/mole, that is, less than the Si-Si bond effort with that of Prof. John Falconer’s energy of 53 kcal/mole. An independent group at the University of Colorado quantum mechanical calculation by Chou, (Boulder). John’s group used Auger et al. (J. Amer. Chem. Soc., 109(1987) Electron Spectroscopy (AES) and 1880)) found 30.7 kcal/mole as the Cu-Si Temperature Programmed Desorption/ bond energy. The reduced energy of Cu-Si Mass Spectrometry (TPD/MS) and we, at bonds compared to Si-Si bonds is Tarrytown, employed X-Ray consistent with copper catalysis and the Photoelectron Spectroscopy (XPS) and fact that it is the alloyed silicon, which is Mass Spectrometry.
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