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La metanólisis catalizada de fosfato de hidroxipropil-p-nitrofenilo como modelo para la reacción de
Josephine S W Tsang1, Alexei A Neverov, R S Brown
1Department of Chemistry, Queen's University, Kingston, Ontario, Canada, K7L 3N6.
Journal of the American Chemical Society
|February 6, 2003
Resumen
El triflato de lantano cataliza la metanólisis del fosfato de hidroxipropil-p-nitrofenilo a través de complejos distintos La3+). Un complejo 2: 2 acelera significativamente la reacción a pH bajo, mientras que un complejo diferente domina a pH alto.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- La catálisis por catálisis.
- La bioquímica es la bioquímica.
Sus antecedentes:
- El fosfato de hidroxipropil-p-nitrofenilo (HPNPP) es un sustrato relevante para la hidrólisis de los ésteres de fosfato.
- Los triflados de lantanuro son ácidos de Lewis con potenciales aplicaciones catalíticas.
Objetivo del estudio:
- Para investigar la metanólisis de HPNPP catalizado por La{OTf}{3).
- Para aclarar el papel del pH y la estequiometría del complejo de lantano en el mecanismo catalítico.
Principales métodos:
- (31) P Espectroscopia de RMN a bajas temperaturas para identificar complejos de lantano-HPNPP.
- Estudios cinéticos que monitorean las constantes de velocidad de pseudo-primer orden bajo diferentes concentraciones de pH y La3+).
Principales resultados:
- En pH ~5.3, se identificaron tres complejos La/HPNPP (1:1, 2:2, 1:2 estequiometría).
- Se observaron dos regímenes de pH: un pH bajo (4.5-7.6) mostró una unión 1:1 con un complejo 2:2 catalíticamente activo, lo que produjo una aceleración de la velocidad de 4.6 x 10 10 veces.
- El pH alto (7.9-10.5) implicaba complejos 1:1, 2:2, y 2:1, con un complejo de saturación que llevaba a una aceleración de 10 y 9 veces a un pH de 8.0.
Conclusiones:
- El mecanismo catalítico de la metanólisis de HPNPP por La ((OTf) ((3) es dependiente del pH, involucrando diferentes estequiometrías del complejo lantano-HPNPP.
- La formación de complejos específicos, particularmente las especies 2:2, es crucial para una mejora significativa de la velocidad en la metanólisis del éster fosfato.
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