Química Orgánica 2 · Rutas de síntesis: reactivos, grupos protectores y planificación en varios pasos
DMAP-catalysed acetylation of 2-phenylethanol
Condiciones: 2-Phenylethanol, acetic anhydride (1.5 equiv), Et₃N (1.5 equiv), DMAP (0.05 equiv), CH₂Cl₂, 25 °C
Dibuja este problema tú mismo
Arrastra desde los electrones que se mueven hasta donde van, o toca uno y luego el otro. Cada flecha se revisa; Pista te ayuda cuando te atascas. No necesitas cuenta.
El mecanismo, paso a paso
Siguiente reproduce las flechas curvas de cada paso y las explica. Los pasos escritos están abajo.
Leer los 7 pasos escritos
DMAP adds to acetic anhydride
The ring nitrogen of DMAP uses its lone pair to attack one carbonyl carbon of acetic anhydride; the C=O π pair moves onto oxygen.
Las flechas curvas
- The ring nitrogen lone pair forms the N–C bond.
- The C=O π pair moves onto oxygen.
Acetate leaves: the acetylpyridinium ion
The oxyanion re-forms C=O and acetate is expelled, leaving the N-acetylpyridinium ion, a far more reactive acylating agent than the anhydride.
Las flechas curvas
- The oxygen lone pair rebuilds the C=O π bond.
- The C–O bond breaks and acetate leaves.
Why does a little DMAP speed things up?
DMAP is a nucleophilic catalyst: it is acylated faster than the alcohol and hands the acyl group on.
The alcohol adds to the acetylpyridinium ion
The hydroxyl oxygen of 2-phenylethanol attacks the acyl carbon and the C=O π pair moves onto oxygen.
Las flechas curvas
- The alcohol oxygen lone pair forms the new O–C bond.
- The C=O π pair moves onto oxygen.
DMAP is released
The oxyanion re-forms C=O and the bond to the ring nitrogen breaks. Neutral DMAP leaves and is free to start another cycle.
Las flechas curvas
- The oxygen lone pair rebuilds the C=O π bond.
- The C–N bond breaks and the pair returns to the ring nitrogen.
Acetate removes the oxonium proton
Acetate takes the proton from the positively charged ester oxygen, giving the neutral ester and acetic acid (neutralised by triethylamine).
Las flechas curvas
- The acetate oxygen lone pair takes the proton.
- The O–H pair stays on the ester oxygen.
2-Phenylethyl acetate
The alcohol is protected as its acetate ester and DMAP is regenerated. An acetate survives mild acid, oxidants such as PCC and acid chlorides, but not Grignard reagents, LiAlH₄ or hydroxide; it is removed with K₂CO₃ or NaOMe in methanol.
Qué vas a practicar
Draw how 4-(dimethylamino)pyridine turns acetic anhydride into an N-acetylpyridinium ion, how 2-phenylethanol is acetylated by that ion, and how the catalyst is released to protect the alcohol as its acetate ester.
Acabas de dibujar cada flecha de este problema.
Cada uno de los 5349 problemas de Orgánica 1 y 2 funciona así: comentarios en cada flecha, pistas cuando te atascas y un modo examen sin pistas. Gratis con una cuenta, sin tarjeta.
¿Atascado con tu propia tarea?
Tómale una foto: el primer escaneo es gratis, sin registrarte
¿Escaneas cada semana? Scan Standard: por unos problemas