Química Orgânica 2 · Ferramentas de oxidação e redução
LiAlH4 reduction of γ-butyrolactone to butane-1,4-diol
Condições: LiAlH4 (1.0 equiv), THF, 0 °C to reflux; then H2O
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 6 passos escritos
Hydride adds to the lactone carbonyl
The Al–H pair forms a new C–H bond at the lactone carbonyl carbon while the C=O π pair moves onto oxygen, giving a tetrahedral alkoxide that is still a ring.
As setas curvas
- The Al–H pair carries the hydrogen to the carbonyl carbon.
- The C=O π pair moves onto oxygen.
The ring opens
The alkoxide lone pair re-forms the C=O bond and the ring C–O bond breaks. The leaving alkoxide stays attached to the other end of the chain, so the product is an open-chain aldehyde carrying an alkoxide.
As setas curvas
- An oxygen lone pair rebuilds the C=O π bond.
- The ring C–O bond breaks; its pair stays on the ring oxygen, which becomes an alkoxide at the end of the chain.
Where did the ring oxygen go?
The ring oxygen was the ester's alkoxy oxygen. It left as an alkoxide but, being part of the same chain, it ends up as the second CH2OH group of the diol.
Second hydride reduces the aldehyde
The aldehyde formed by ring opening is more electrophilic than the starting lactone, and it takes a second hydride at once.
As setas curvas
- The Al–H pair forms the second new C–H bond at the aldehyde carbon.
- The C=O π pair moves onto oxygen, giving a second alkoxide.
Water protonates both alkoxides
On workup each alkoxide oxygen takes a proton from water, giving the neutral diol.
As setas curvas
- One alkoxide lone pair takes a proton from water.
- That water O–H pair stays on oxygen as hydroxide.
- The other alkoxide takes a proton from a second water.
- That O–H pair stays on oxygen as hydroxide.
Butane-1,4-diol
Both ends of the four-carbon chain now carry CH2OH groups: the carbonyl carbon and the carbon that held the ring oxygen.
O que você vai praticar
Draw the LiAlH4 reduction of γ-butyrolactone: hydride addition, ring opening of the tetrahedral intermediate to an alkoxy aldehyde, the second hydride addition and the water workup that gives butane-1,4-diol.
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