Química Orgânica 2 · Adição e condensação aldólica
(E,E)-Dibenzalacetone: the second condensation
Condições: NaOH, EtOH/H2O, benzaldehyde (2 equiv)
Desenhe este problema você mesmo
Arraste dos elétrons que se movem até onde eles vão, ou toque em um e depois no outro. Cada seta é verificada; Dica ajuda quando você travar. Não precisa de conta.
O mecanismo, passo a passo
Próximo mostra as setas curvas de cada passo e as explica. Os passos escritos estão abaixo.
Ler todos os 7 passos escritos
Hydroxide forms the methyl enolate
With two equivalents of benzaldehyde, the benzalacetone formed first still has a methyl group α to the carbonyl. Hydroxide removes one of its hydrogens; the vinylic hydrogens cannot form an enolate.
As setas curvas
- Hydroxide takes a methyl α-hydrogen.
- The C–H pair forms the enolate C=C bond.
- The C=O π pair moves onto oxygen.
Addition to the second benzaldehyde
The enolate carbon attacks the second benzaldehyde, forming a new C–C bond and an alkoxide.
As setas curvas
- The oxygen lone pair re-forms the C=O.
- The enolate π pair forms the new C–C bond.
- The aldehyde π pair moves onto oxygen.
Protonation of the alkoxide
Water protonates the alkoxide, giving the β-hydroxy ketone and regenerating hydroxide.
As setas curvas
- The alkoxide takes a proton from water.
- The O–H pair stays on oxygen as hydroxide.
Second enolization
Hydroxide removes the remaining hydrogen on the carbon between the carbonyl and the carbinol carbon, forming the enolate that will expel hydroxide.
As setas curvas
- Hydroxide takes the α-hydrogen.
- The C–H pair forms the enolate C=C bond.
- The C=O π pair moves onto oxygen.
Why stop at two?
Each condensation consumes the two α-hydrogens on one side of the carbonyl.
E1cB loss of hydroxide
The enolate re-forms C=O and expels hydroxide from the benzylic carbon. The new C=C completes a fully conjugated cross-conjugated dienone, and the E geometry is favoured on both sides.
As setas curvas
- The oxygen lone pair re-forms the C=O.
- The enolate π pair forms the new C=C bond.
- The C–O pair leaves as hydroxide.
(E,E)-Dibenzalacetone
(E,E)-Dibenzalacetone (1,5-diphenylpenta-1,4-dien-3-one) precipitates as a yellow solid; hydroxide is regenerated.
O que você vai praticar
Draw the second Claisen–Schmidt condensation: the methyl enolate of (E)-benzalacetone adds to a second benzaldehyde and loses hydroxide by E1cB to give (E,E)-dibenzalacetone.
Você acabou de desenhar cada seta deste problema.
Cada um dos 5349 problemas de Orgânica 1 e 2 funciona assim: feedback em cada seta, dicas quando você travar e um modo prova sem dicas. Grátis com uma conta, sem cartão.
Travou na sua própria lição?
Tire uma foto: o primeiro scan é grátis, sem cadastro
Você escaneia toda semana? Scan Standard: por cerca de problemas