Química Orgânica 2 · Síntese e transformação de aminas
Gabriel synthesis — phthalimide alkylation and deprotection
Condições: Potassium phthalimide and bromoethane in polar aprotic solvent, then separate forcing aqueous base hydrolysis. Two hydroxides are added in turn; countercations are omitted throughout. Collapse and proton transfer are drawn separately to show electron flow, not to suggest that amide anions persist in water.
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Próximo mostra as setas curvas de cada passo e as explica. Os passos escritos estão abaixo.
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Protected nitrogen and alkyl electrophile
The imide nitrogen forms the alkyl C–N bond. The C–Br pair leaves as bromide.
As setas curvas
- The imide nitrogen forms the alkyl C–N bond.
- The C–Br pair leaves as bromide.
First hydrolysis
Hydroxide adds at an imide carbonyl carbon. The carbonyl pair moves to oxygen. Alkylation has ended. Aqueous hydroxide is added; all prior atoms remain.
Nota: Alkylation has ended. Aqueous hydroxide is added; all prior atoms remain.
As setas curvas
- Hydroxide adds at an imide carbonyl carbon.
- The carbonyl pair moves to oxygen.
Continue the first acyl substitution
The original oxygen restores its carbonyl. The acyl C–N pair leaves with nitrogen, opening the imide ring rather than breaking the alkyl C–N bond.
As setas curvas
- The original oxygen restores its carbonyl.
- The acyl C–N pair leaves with nitrogen, opening the imide ring rather than breaking the alkyl C–N bond.
First acid–base trapping event
The nitrogen anion accepts the newly formed carboxylic acid proton. The O–H pair gives a carboxylate and traps the ring-opened product.
As setas curvas
- The nitrogen anion accepts the newly formed carboxylic acid proton.
- The O–H pair gives a carboxylate and traps the ring-opened product.
Second hydrolysis
A second hydroxide adds at the remaining amide carbonyl. The second carbonyl pair moves to oxygen. A second aqueous hydroxide equivalent is added. The monoamide is not the endpoint: forcing hydrolysis also removes this acyl group.
Nota: A second aqueous hydroxide equivalent is added. The monoamide is not the endpoint: forcing hydrolysis also removes this acyl group.
As setas curvas
- A second hydroxide adds at the remaining amide carbonyl.
- The second carbonyl pair moves to oxygen.
Continue the second acyl substitution
The original carbonyl oxygen donates back to carbon. The remaining acyl C–N pair moves to nitrogen. Collapse and proton transfer are drawn separately to show the electron flow. This does not mean an ethylamide anion accumulates in water.
As setas curvas
- The original carbonyl oxygen donates back to carbon.
- The remaining acyl C–N pair moves to nitrogen.
Final acid–base trapping event
The nitrogen anion accepts the second carboxylic acid proton. The acid O–H pair remains on the second carboxylate oxygen.
As setas curvas
- The nitrogen anion accepts the second carboxylic acid proton.
- The acid O–H pair remains on the second carboxylate oxygen.
Primary amine and phthalate
The nitrogen–ethyl bond made in the first event survives both acyl cleavages. The nitrogen gains two explicit hydrogens to become neutral ethylamine; both original carbonyl carbons remain in phthalate. Phthalate (−2) and bromide (−1) conserve the charge of imide plus the two hydroxide inputs.
O que você vai praticar
Carry an imide nitrogen through alkylation and both hydrolytic acyl cleavages without confusing alkyl C–N retention with acyl C–N loss.
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