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Aceleración solvofóbica de las reacciones de Diels-Alder en dióxido de carbono supercrítico

Jin Qian¹, Michael T Timko, Andrew J Allen

¹Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Journal of the American Chemical Society

|April 29, 2004

Resumen

La velocidad de reacción de Diels-Alder aumentó significativamente en el dióxido de carbono supercrítico (scCO(2)), mostrando una aceleración de 25 veces en comparación con el acetonitrilo. Esta mayor reactividad en scCO(2) se atribuye a un mecanismo solvófobo.

Área de la Ciencia:

La cinética de las sustancias químicas.
Tecnología de fluidos supercríticos en tecnología de fluidos supercríticos.

Sus antecedentes:

La reacción de Diels-Alder es una transformación orgánica fundamental.
El dióxido de carbono supercrítico (scCO(2) ofrece propiedades únicas de disolvente para las reacciones químicas.

Objetivo del estudio:

Investigar la cinética de la reacción de Diels-Alder entre la N-etilmaleimida y el 9-hidroximetilantraceno en scCO(2).
Para aclarar los factores que influyen en las tasas de reacción y los mecanismos en scCO(2).

Principales métodos:

Espectroscopia de absorción UV/vis in situ para monitorear el consumo de reactivo.
Variación de las condiciones de reacción (temperatura y presión) para estudiar los efectos de densidad.
Mediciones de solubilidad y comparaciones de velocidad en disolventes convencionales.

Principales resultados:

Las tasas de reacción en scCO(2) fueron hasta 25 veces más rápidas que en acetonitril a 45°C.
Se observó una relación inversa entre la velocidad de reacción y la densidad/presión del fluido.
Los grandes volúmenes de activación positiva (350 cm3 mol-1) indicaron un mecanismo de reacción específico.

Conclusiones:

Un mecanismo solvófobo explica la aceleración de la velocidad y la dependencia de presión / densidad en scCO.
Los resultados avanzan en la comprensión de la reactividad en fluidos supercríticos.
Proporciona una base para seleccionar las reacciones aceleradas por scCO(2).

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