Química Orgânica 2 · Ferramentas de oxidação e redução
Jones oxidation of butan-1-ol to butanoic acid
Condições: CrO3 (1.4 equiv), H2SO4, H2O/acetone (Jones reagent), 0 °C to 25 °C
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Hydronium protonates chromic acid
Hydronium protonates a Cr–OH group of chromic acid, preparing it to leave as water.
As setas curvas
- A Cr–OH oxygen lone pair takes a proton from hydronium.
- The hydronium O–H pair stays on oxygen, leaving water.
The alcohol attacks chromium
The alcohol oxygen bonds to chromium as the protonated hydroxyl leaves as water.
As setas curvas
- An alcohol oxygen lone pair forms the O–Cr bond.
- The Cr–O bond to the protonated hydroxyl breaks, releasing water.
Water deprotonates the chromate ester
Water removes the proton from the oxonium oxygen, giving the neutral chromate ester of butan-1-ol.
As setas curvas
- A water lone pair takes the proton on the ester oxygen.
- The O–H pair stays on the ester oxygen.
Elimination gives butanal
Water removes one carbinol hydrogen. The C–H pair becomes the C=O π bond and the O–Cr pair goes to chromium, giving butanal and Cr(IV).
As setas curvas
- A water lone pair takes a carbinol hydrogen.
- The C–H pair becomes the C=O π bond.
- The O–Cr pair leaves with chromium.
Does it stop at butanal?
In aqueous acid the aldehyde is hydrated, and the hydrate behaves like an alcohol toward chromium(VI).
Hydronium protonates the aldehyde
Hydronium protonates the carbonyl oxygen of butanal, making its carbon more electrophilic toward water.
As setas curvas
- A carbonyl oxygen lone pair takes a proton from hydronium.
- The hydronium O–H pair stays on oxygen, leaving water.
Water adds to the protonated aldehyde
Water attacks the carbonyl carbon and the C=O π pair moves onto the protonated oxygen.
As setas curvas
- A water lone pair forms the new C–O bond.
- The C=O π pair moves onto oxygen.
Water deprotonates to the hydrate
Another water molecule removes a proton from the oxonium oxygen, giving neutral butane-1,1-diol, the aldehyde hydrate.
As setas curvas
- A water lone pair takes the proton.
- The O–H pair stays on the hydrate oxygen.
Hydronium protonates a second chromic acid
A second molecule of chromic acid is activated the same way: hydronium protonates one of its Cr–OH groups.
As setas curvas
- A Cr–OH oxygen lone pair takes a proton from hydronium.
- The hydronium O–H pair stays on oxygen, leaving water.
The hydrate attacks chromium
One OH of the hydrate bonds to chromium as water leaves, just as the alcohol did.
As setas curvas
- A hydrate oxygen lone pair forms the O–Cr bond.
- The Cr–O bond to the protonated hydroxyl breaks, releasing water.
Water deprotonates the second chromate ester
Water removes the proton from the oxonium oxygen, giving the neutral chromate ester of the hydrate.
As setas curvas
- A water lone pair takes the proton on the ester oxygen.
- The O–H pair stays on the ester oxygen.
Second elimination gives butanoic acid
Water removes the last hydrogen on the oxygen-bearing carbon; the C–H pair becomes the C=O π bond and the O–Cr pair goes to chromium, giving butanoic acid.
As setas curvas
- A water lone pair takes the hydrogen on the oxygen-bearing carbon.
- The C–H pair becomes the C=O π bond.
- The O–Cr pair leaves with chromium.
Butanoic acid
Two chromate-ester oxidations have taken the primary alcohol through butanal and its hydrate to butanoic acid; its second oxygen came from water.
O que você vai praticar
Draw the Jones oxidation of butan-1-ol through butanal and its hydrate: chromate ester formation, elimination, acid-catalysed hydration, a second chromate ester and a second elimination that give butanoic acid.
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