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Mecanismo de alquilación del fenol en la zeolita H-BEA utilizando la espectroscopia de RMN en estado sólido in situ

Zhenchao Zhao¹, Hui Shi¹, Chuan Wan¹

¹Institute for Integrated Catalysis, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99352, United States.

Journal of the American Chemical Society

|June 20, 2017

Resumen

Los catalizadores de ácido sólido facilitan la alquilación del fenol. La alquilación de fenol con ciclohexanol requiere una deshidratación previa al ciclohexeno, ya que los dímeros de ciclohexanol inhiben la formación reactiva de electrófilos.

Área de la Ciencia:

Catálisis
Química orgánica
Química Física

Sus antecedentes:

La alquilación de fenol es una reacción clave en la síntesis orgánica.
La comprensión de los mecanismos de reacción es crucial para el desarrollo de catalizadores.
Los catalizadores de ácido sólido ofrecen ventajas medioambientales y de separación.

Objetivo del estudio:

Elucidar el mecanismo de reacción de la alquilación de fenol catalizada por ácido sólido.
Investigar el papel de la deshidratación del ciclohexanol en la vía de reacción.
Identificar el electrofilo reactivo y su mecanismo de formación.

Principales métodos:

Se utilizó la espectroscopia de RMN MAS in situ 13C para estudiar la reacción.
Se utilizó el etiquetado del isótopo 13C para rastrear los intermedios de reacción.
La reacción se llevó a cabo en un disolvente apolar (decalina).

Principales resultados:

La alquilación del fenol con el ciclohexanol solo se produce después de la deshidratación del ciclohexanol al ciclohexeno.
El ion ciclohexilo carbenio, el electrofilo reactivo, se forma a través de la protonación del ciclohexeno.
Los dímeros de ciclohexanol protonados en los sitios de ácido de Brønsted impiden la adsorción de ciclohexeno y la formación de iones de carbenio.
Los dímeros de ciclohexanol protonados se deshidratan sin formación de iones de carbenio.

Conclusiones:

La secuencia de reacción está dictada por la formación del electrofilo reactivo.
La presencia de ciclohexanol inhibe la formación de iones de carbenio necesarios para la alquilación.
La reorganización intramolecular del éter fenílico de ciclohexilo no es una vía de alquilación significativa.

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