Química Orgânica 2 · Hidrólise e esterificação
Saponification of triacetin to glycerol
Condições: NaOH (3 equiv), H2O
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O mecanismo, passo a passo
Próximo mostra as setas curvas de cada passo e as explica. Os passos escritos estão abaixo.
Ler todos os 11 passos escritos
Hydroxide adds to the primary acetate
Hydroxide adds to the carbonyl carbon of the acetate ester on the primary glycerol oxygen; each ester reacts independently, so one equivalent of hydroxide is used per ester.
As setas curvas
- A hydroxide lone pair forms the new C–O bond.
- The C=O π electrons move onto the oxygen.
Collapse releases the glycerol alkoxide
The oxide lone pair re-forms the C=O and the glycerol oxygen leaves as an alkoxide, giving acetic acid.
As setas curvas
- The O⁻ lone pair re-forms the carbonyl π bond.
- The C–O bond breaks onto the glycerol oxygen.
Proton transfer to the alkoxide
The alkoxide takes the acidic proton of acetic acid, giving an alcohol and acetate. This irreversible step drives each saponification.
As setas curvas
- The alkoxide lone pair takes the acidic proton.
- The O–H bond pair stays on the atom that loses the proton.
How much base?
Count the ester groups.
Hydroxide adds to the secondary acetate
Hydroxide adds to the carbonyl carbon of the acetate ester on the secondary glycerol oxygen; each ester reacts independently, so one equivalent of hydroxide is used per ester.
As setas curvas
- A hydroxide lone pair forms the new C–O bond.
- The C=O π electrons move onto the oxygen.
Collapse releases the glycerol alkoxide
The oxide lone pair re-forms the C=O and the glycerol oxygen leaves as an alkoxide, giving acetic acid.
As setas curvas
- The O⁻ lone pair re-forms the carbonyl π bond.
- The C–O bond breaks onto the glycerol oxygen.
Proton transfer to the alkoxide
The alkoxide takes the acidic proton of acetic acid, giving an alcohol and acetate. This irreversible step drives each saponification.
As setas curvas
- The alkoxide lone pair takes the acidic proton.
- The O–H bond pair stays on the atom that loses the proton.
Hydroxide adds to the second primary acetate
Hydroxide adds to the carbonyl carbon of the acetate ester on the second primary glycerol oxygen; each ester reacts independently, so one equivalent of hydroxide is used per ester.
As setas curvas
- A hydroxide lone pair forms the new C–O bond.
- The C=O π electrons move onto the oxygen.
Collapse releases the glycerol alkoxide
The oxide lone pair re-forms the C=O and the glycerol oxygen leaves as an alkoxide, giving acetic acid.
As setas curvas
- The O⁻ lone pair re-forms the carbonyl π bond.
- The C–O bond breaks onto the glycerol oxygen.
Proton transfer to the alkoxide
The alkoxide takes the acidic proton of acetic acid, giving an alcohol and acetate. This irreversible step drives each saponification.
As setas curvas
- The alkoxide lone pair takes the acidic proton.
- The O–H bond pair stays on the atom that loses the proton.
Glycerol and acetate
Glycerol and three acetates (Na⁺ omitted) form. With long-chain fatty acid esters the same reaction gives soap.
O que você vai praticar
Draw the three hydroxide additions, alkoxide losses and proton transfers that saponify all three esters of triacetin to glycerol.
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