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1Department of Biochemistry and Applied Chemistry, Kurume National College of Technology, Komorinomachi, Kurume 830-8555, Japan.
Journal of the American Chemical Society
|December 21, 2006
Resumen
Se monitoreó la pureza quiral del tosilato de etilo (S)-1-(3-nitrofenilo) durante la solvolisis. La isomerización se produce a través de una vía que evita los intermediarios comunes de pares de iones, lo que sugiere un mecanismo de preasociación gradual para la solvolisis.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Mecanismos de reacción Mecanismos de reacción
- La estereoquímica es la estereoquímica.
Sus antecedentes:
- Investigar los resultados estereoquímicos de las reacciones de solvolisis es crucial para comprender los mecanismos de reacción.
- El comportamiento de los tosilatos quirales bajo condiciones de solvolisis proporciona información sobre la ionización y la formación intermedia.
Objetivo del estudio:
- Para determinar los cambios de pureza quiral de (S) -1- ((3-Nitrophenyl) etil tosilato durante la solvolisis.
- Para dilucidar el mecanismo de la isomerización y racemization en este sistema.
- Para comparar las tasas de racemización e isomerización con las predicciones teóricas.
Principales métodos:
- Síntesis de tosilato de etilo (S)-1-(3-nitrofenilo) con un alto exceso enantiomérico (>99%).
- Monitoreo de los cambios de pureza quiral durante la solvolisis en una mezcla 50:50 trifluoroetanol/agua.
- Análisis cinético para determinar las constantes de velocidad para la racemización (k ((rac)) y la isomerización (k ((iso)).
Principales resultados:
- Se observó una racemicidad mínima (0,5% (R) -2-OTs) después de dos vidas medias.
- La constante de velocidad de racemización calculada (k(rac) ≈ 4 x 10^-6 s^-1) es significativamente más pequeña que la constante de velocidad de isomerización (k(iso) = 3.2 x 10^-4 s^-1).
- El k observado es también menor que los valores predichos para un mecanismo que involucra un intermediario común de pares de iones.
Conclusiones:
- La reacción de isomerización procede predominantemente a través de una vía que evita la formación de un intermediario común de pares de iones.
- La solvolización de 2-OTs puede ocurrir a través de un mecanismo de preasociación gradual, que implica la reorganización del disolvente antes de la ionización del sustrato.
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