Química Orgánica 2 · Sustitución de acilo y elección del derivado
Acetic acid by acid hydrolysis of acetamide
Condiciones: H3O⁺, Δ
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 8 pasos escritos
Protonate the carbonyl oxygen
Hydronium protonates the amide on oxygen (the more basic site, because the resulting cation is resonance-stabilised by nitrogen). This activates the poorly electrophilic amide carbonyl.
Las flechas curvas
- A carbonyl oxygen lone pair bonds to the proton of hydronium.
- The O–H pair returns to the water oxygen.
Water adds
Water attacks the protonated carbonyl carbon; the C=O⁺ π pair moves onto oxygen, giving a tetrahedral oxonium ion.
Las flechas curvas
- A water oxygen lone pair forms the new O–C bond.
- The C=O⁺ π pair moves onto oxygen.
Water removes the oxonium proton
A water molecule takes the proton from the added water oxygen, giving a neutral tetrahedral intermediate and hydronium.
Las flechas curvas
- A water lone pair bonds to the O–H proton.
- The O–H pair returns to oxygen.
Protonate the nitrogen
Hydronium protonates the NH2 group, turning it into a neutral ammonia leaving group. In the tetrahedral intermediate nitrogen is no longer conjugated with C=O, so it is basic.
Las flechas curvas
- The nitrogen lone pair bonds to the proton.
- The O–H pair returns to the water oxygen.
Leaving group
Amide ion (NH2⁻) is far too basic to leave; protonated nitrogen leaves as neutral ammonia.
Ammonia leaves
An OH lone pair re-forms the C=O π bond (as a protonated carbonyl) and pushes out ammonia.
Las flechas curvas
- The OH lone pair re-forms the C=O π bond.
- The C–N pair leaves with nitrogen as ammonia.
Ammonia takes the proton
Ammonia, a much stronger base than the protonated acid, removes its proton. Forming ammonium makes the overall hydrolysis irreversible in acid.
Las flechas curvas
- The ammonia lone pair bonds to the O–H proton.
- The O–H pair returns to oxygen, giving the neutral C=O.
Acetic acid
Acetic acid forms with ammonium ion. Amides need hot strong acid and long heating because the amide carbonyl is stabilised by nitrogen resonance; capturing ammonia as NH4⁺ pulls the reaction to completion.
Qué vas a practicar
Hydrolyse acetamide in hot aqueous acid: protonate the carbonyl, add water, shuttle protons onto nitrogen, expel ammonia and capture it as ammonium.
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