Química Orgânica 2 · Hidrólise e esterificação
Acid hydrolysis of acetonitrile to acetic acid
Condições: H2SO4, H2O, Δ
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Ler todos os 13 passos escritos
Protonate the nitrile nitrogen
Hydronium protonates the nitrile nitrogen, giving a nitrilium ion whose carbon is strongly electrophilic.
As setas curvas
- The nitrile nitrogen lone pair takes the proton.
- The O–H bond pair stays on the atom that loses the proton.
Water adds to the nitrilium carbon
Water attacks the nitrilium carbon; one π bond moves onto nitrogen.
As setas curvas
- A water lone pair forms the new C–O bond.
- One C≡N π bond moves onto nitrogen.
Deprotonate to the imidic acid
Water removes the proton from the oxonium oxygen, giving the imidic acid, the enol-like tautomer of acetamide.
As setas curvas
- A lone pair on the base takes the proton.
- The O–H bond pair stays on the atom that loses the proton.
Protonate the imidic acid nitrogen
Hydronium protonates the C=N nitrogen, the first half of the tautomerisation to the amide.
As setas curvas
- The imine nitrogen lone pair takes the proton.
- The O–H bond pair stays on the atom that loses the proton.
Remove the O–H proton to give acetamide
Water removes the O–H proton; those electrons form the C=O while the C=N π pair returns to nitrogen. The more stable amide tautomer results.
As setas curvas
- A water lone pair takes the O–H proton.
- The O–H bond pair forms the C=O π bond.
- The C=N π pair moves onto nitrogen.
Can it stop at the amide?
Compare the conditions.
Protonate the amide oxygen
Hydronium protonates acetamide on oxygen, activating it for a second water addition.
As setas curvas
- The carbonyl oxygen lone pair takes the proton.
- The O–H bond pair stays on the atom that loses the proton.
Water adds to the protonated amide
A second water molecule adds to the carbonyl carbon.
As setas curvas
- A water lone pair forms the new C–O bond.
- The C=O π electrons move onto the oxygen.
Deprotonate the added water
Water removes the extra proton from the new oxonium oxygen.
As setas curvas
- A lone pair on the base takes the proton.
- The O–H bond pair stays on the atom that loses the proton.
Protonate the nitrogen
Hydronium protonates the sp³ nitrogen so it can leave as ammonia.
As setas curvas
- The nitrogen lone pair takes the proton.
- The O–H bond pair stays on the atom that loses the proton.
Ammonia leaves
An OH lone pair re-forms the C=O π bond and ammonia departs.
As setas curvas
- An oxygen lone pair forms the C=O π bond.
- The C–N bond breaks onto nitrogen.
Ammonia is protonated
Ammonia takes the proton from protonated acetic acid, giving ammonium and acetic acid; this makes the overall hydrolysis irreversible.
As setas curvas
- The ammonia lone pair takes the proton.
- The O–H bond pair stays on the atom that loses the proton.
Acetic acid and ammonium
Acetic acid and ammonium hydrogen sulfate (anion omitted) form: two waters were consumed and the nitrogen ends as NH4⁺.
O que você vai praticar
Draw the full acid hydrolysis of acetonitrile: water addition to the protonated nitrile, tautomerisation to acetamide, then acid hydrolysis of acetamide to acetic acid and ammonium.
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