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Transferencia concertada protón-electrón en la oxidación de fenoles enlazados con hidrógeno
Ian J Rhile1, Todd F Markle, Hirotaka Nagao
1Department of Chemistry, Campus Box 351700, University of Washington, Seattle, Washington 98195-1700, USA.
Journal of the American Chemical Society
|May 4, 2006
Resumen
Se estudiaron las reacciones de transferencia de electrones acoplados a protones (PCET) que involucran fenoles y bases colgantes. Estas reacciones se producen a través de la transferencia concertada de protones-electrones (CPET), no por mecanismos escalonados, con energías de reorganización significativas.
Área de la Ciencia:
- Química Física es la química física.
- La electroquímica es electroquímica.
- La cinética química es la cinética química.
Sus antecedentes:
- Los fenoles con bases colgantes enlazadas con hidrógeno (HOAr-B) son sistemas modelo para el estudio de la transferencia de electrones acoplados a protones (PCET).
- Comprender los mecanismos de la PCET es crucial para varios procesos químicos y biológicos.
Objetivo del estudio:
- Para investigar el mecanismo de oxidación de tres fenoles con bases colgantes enlazadas con hidrógeno (amina primaria, imidazol, piridina) en acetonitrilo.
- Determinar los potenciales redox y las vías de reacción, diferenciando específicamente entre la transferencia concertada protón-electrón (CPET) y los mecanismos escalonados.
- Para analizar la cinética y la termodinámica de estas reacciones PCET utilizando métodos electroquímicos y químicos.
Principales métodos:
- Oxidación química utilizando varios oxidantes de un solo electrón.
- Oxidación electroquímica casi reversible.
- Análisis de argumentos termoquímicos, efectos de isótopos cinéticos y teoría de Marcus para elucidación mecanicista.
Principales resultados:
- Los productos de oxidación son los radicales fenoxilo con transferencia de protones a la base, (*)OAr-BH(+), lo que indica un proceso PCET.
- Los potenciales redox se reducen debido a la fuerza motriz para la transferencia de protones.
- La evidencia apoya firmemente un mecanismo concertado de transferencia de protones-electrones (CPET), descartando la transferencia inicial de electrones o protones.
- Se observaron grandes energías de reorganización (λ = 2356 kcal mol−1) para el CPET.
- Las constantes de velocidad para la transferencia heterogénea de electrones se alinean con las predicciones de la teoría adiabática de Marcus.
Conclusiones:
- La oxidación de fenoles con bases colgantes se produce a través de un mecanismo CPET.
- La cinética y la termodinámica observadas son consistentes con la teoría adiabática de Marcus.
- Estos hallazgos proporcionan información detallada sobre las reacciones CPET en las que se producen transferencias de protones y electrones a diferentes sitios.
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