Química Orgánica 2 · Síntesis y transformación de aminas
N,N-Dimethylbenzylamine by Eschweiler–Clarke methylation
Condiciones: HCHO (excess), HCOOH, Δ
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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 14 pasos escritos
Amine adds to formaldehyde
The benzylamine nitrogen attacks the very electrophilic formaldehyde carbon and the C=O π pair moves onto oxygen.
Las flechas curvas
- The nitrogen lone pair forms the N–C bond.
- The C=O π pair moves onto oxygen.
Formic acid protonates the alkoxide
Formic acid, the strongest acid present, protonates the alkoxide oxygen.
Las flechas curvas
- The alkoxide takes the formic acid proton.
- The O–H pair stays on oxygen as formate.
Formate removes an N–H proton
Formate takes a proton from the ammonium nitrogen, giving the neutral hemiaminal.
Las flechas curvas
- Formate takes the N–H proton.
- The N–H pair returns to nitrogen.
Formic acid protonates the OH
Formic acid protonates the hemiaminal OH so it can leave as water.
Las flechas curvas
- The OH oxygen takes the formic acid proton.
- The O–H pair stays on oxygen as formate.
Water leaves; the iminium forms
The nitrogen lone pair forms the C=N π bond as water leaves, giving an iminium ion.
Las flechas curvas
- The nitrogen lone pair forms the C=N π bond.
- The C–O pair leaves with water.
Formate delivers hydride
Formate gives the hydride on its carbon to the iminium carbon; its O⁻ lone pair forms the second C=O, so CO2 is released. This makes the first N-methyl group.
Las flechas curvas
- The formate O⁻ lone pair forms a C=O bond.
- The C–H pair moves as hydride to the iminium carbon.
- The C=N π pair moves onto nitrogen.
Why it stops at the tertiary amine
Iminium formation needs an N–H.
Second round: add formaldehyde again
The secondary amine N-methylbenzylamine is still nucleophilic and adds to a second formaldehyde.
Las flechas curvas
- The nitrogen lone pair attacks formaldehyde.
- The C=O π pair moves onto oxygen.
Protonate the alkoxide
Formic acid protonates the new alkoxide.
Las flechas curvas
- The alkoxide takes the formic acid proton.
- The O–H pair stays on oxygen.
Remove the last N–H proton
Formate takes the remaining N–H proton, giving the neutral hemiaminal.
Las flechas curvas
- Formate takes the N–H proton.
- The N–H pair returns to nitrogen.
Protonate the OH again
Formic acid protonates the hemiaminal OH.
Las flechas curvas
- The OH oxygen takes the proton.
- The O–H pair stays on oxygen as formate.
Lose water to the second iminium
The nitrogen lone pair pushes out water, giving an iminium ion with no N–H.
Las flechas curvas
- The nitrogen lone pair forms the C=N π bond.
- The C–O pair leaves with water.
Second hydride transfer
A second formate delivers hydride to the iminium carbon and leaves as CO2, installing the second methyl group.
Las flechas curvas
- The formate O⁻ lone pair forms a C=O bond.
- The C–H pair moves as hydride to the iminium carbon.
- The C=N π pair moves onto nitrogen.
N,N-Dimethylbenzylamine
N,N-Dimethylbenzylamine forms with two CO2 and two water molecules. Loss of CO2 makes each hydride transfer irreversible.
Qué vas a practicar
Draw both rounds of formaldehyde addition, iminium formation and hydride transfer from formate (with CO2 loss) that convert benzylamine into N,N-dimethylbenzylamine.
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