Química Orgânica 2 · Hidrólise e esterificação
Hydrolyze an N-substituted amide
Condições: N-Methylacetamide in heated aqueous acid. Track the forward hydrolysis pathway through carboxylic acid and methylammonium; the persistent acid counteranion is omitted throughout.
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O mecanismo, passo a passo
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Acidic reactant encounter
The explicit hydronium supplies the activation proton. Its conjugate water is retained as the proton shuttle throughout this pathway.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Activated carbonyl
Water adds through oxygen, producing a three-coordinate incoming oxygen and a neutral former carbonyl hydroxyl.
As setas curvas
- The nucleophile uses a lone pair to form the new σ bond.
- The C=O π electrons move to oxygen so carbon keeps eight electrons.
First solvent-mediated proton exchange
Water removes a proton from the incoming oxygen. This separate transfer avoids an unsupported direct intramolecular proton jump.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Prepare the leaving group
The tetrahedral nitrogen is protonated before C–N cleavage; an amide anion is not expelled.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Tetrahedral intermediate in acid
The former carbonyl hydroxyl restores the pi bond while retaining its proton, so the acyl product is initially O-protonated. The leaving group is neutral after accepting the C–leaving-group pair.
As setas curvas
- An oxygen lone pair forms the C=O π bond again.
- The leaving group takes the electrons from the bond that breaks.
Resolve the activated product
Water removes the carbonyl-oxygen proton and restores hydronium. Every oxygen retains its identity through addition and elimination.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Product speciation in the acidic medium
The amine produced by hydrolysis is basic enough to consume the regenerated hydronium. Under the stated acidic conditions, finish at the ammonium carboxylic acid rather than a free amine.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Products
C–N cleavage gives a carboxylic acid and an ammonium group. The incoming water oxygen becomes the acid hydroxyl; the original carbonyl oxygen remains the carbonyl. The net positive charge now resides on nitrogen, with the omitted spectator anion unchanged.
O que você vai praticar
Avoid expelling an amide anion and distinguish catalyst regeneration from final amine protonation.
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