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Interacción de un dinitroaromático débilmente ácido con las alquilaminas: evitando la trampa de Meisenheimer

Eric J Olson¹, Teng T Xiong, Christopher J Cramer

¹Department of Chemistry and Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.

Journal of the American Chemical Society

|July 9, 2011

Resumen

El color azul en las soluciones de 2,4-dinitrotolueno (DNT) y aminas no se debe a los complejos de Meisenheimer, sino más bien a la desprotonación de DNT. Esta desprotonación, aunque es una especie menor, es responsable del color observado.

Área de la Ciencia:

Química orgánica es la química orgánica.
Química Física es la química física.
La espectroscopia es una técnica de espectroscopia.

Sus antecedentes:

Se sabe que los polinitroaromáticos, como el 2,4-dinitrotolueno (DNT), forman complejos σ aniónicos (complejos de Meisenheimer).
Asunciones anteriores vinculaban la formación del complejo de Meisenheimer con el color azul observado en soluciones de DNT y aminas.

Objetivo del estudio:

Para investigar la causa del color azul en las soluciones de DNT-amina.
Para determinar si los complejos de Meisenheimer son las especies primarias responsables del color observado.
Para caracterizar con precisión las interacciones entre DNT y varias aminas.

Principales métodos:

Espectroscopia de resonancia magnética nuclear de protones (RMN) para evaluar los desplazamientos de protones DNT.
Cálculos funcionales de densidad para modelar complejos DNT-etilamina.
Espectroscopia ultravioleta visible (UV / vis) y análisis del componente principal para identificar las especies absorbentes.
Análisis de la trama de Job para cuantificar la formación compleja y los equilibrios.
Experimentos de titulación para determinar los valores de pK (a).

Principales resultados:

Los espectros de RMN mostraron cambios mínimos, lo que indica que el DNT retiene en gran medida la aromaticidad.
Los cálculos funcionales de densidad sugirieron que los complejos de Meisenheimer son altos en energía libre y están presentes en concentraciones muy pequeñas.
El análisis espectral UV / vis reveló una especie absorbente principal, pero la asociación 1: 1 no pudo explicar completamente los espectros.
El análisis de la trama de Job se explicó mejor por la desprotonación de DNT, con aminas que actúan como bases.
Se determinó que el pK (a) consistente de DNT en el dimetilsulfóxido era de 15,3 ± 0,2.2.

Conclusiones:

El color azul en las soluciones de DNT-amina proviene del DNT desprotonado, no de los complejos de Meisenheimer.
Los equilibrios de desprotonación se encuentran muy cerca del DNT no reaccionado, lo que hace que las especies de color sean un componente menor e indetectable por RMN.
Este estudio aclara la base química para el color y proporciona una pK fiable para DNT en DMSO.

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