August 22, 2019, 01:11:39 AM
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Topic: Amide LiAlH4 - Reactionmechanism  (Read 180 times)

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Offline Nozon

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Amide LiAlH4 - Reactionmechanism
« on: August 08, 2019, 12:24:22 PM »
This may be theoretical and unknown but I am wondering how LiAlH4 exactly reacts with an amide.

My book refers it as a hydrid ion makes an nucleophilic attack on the alpha-carbon, forcing the pi-bound of Oxygen to go up to itself and makes an negative charge and then Al is steps in and bind oxygen, making it a good leaving group, so that nitrogen can make a pi-bound to the alpha-carbon and become a cation. (Iminium Ion).
A new nucleophilic attack by a hydrid ion from a new LiAlH4 removes the pi bound between N and C and neutralize the molecule into an amine.

My question is here, what is the positively charged lithium's role? I would I be wrong to assume it destabilize the oxygen's pi-bound (due to it negative polarity) to the alpha carbon at first, so a nucleophilic attack can occur?


Offline rolnor

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Re: Amide LiAlH4 - Reactionmechanism
« Reply #1 on: August 08, 2019, 03:43:06 PM »
I think you can reduce an amide with AlH3, its the hydride and aluminum that is important, lithium not so much.

Offline Nozon

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Re: Amide LiAlH4 - Reactionmechanism
« Reply #2 on: August 09, 2019, 05:09:25 AM »
Rolnor - okay thanks a lot.

Offline kriggy

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Re: Amide LiAlH4 - Reactionmechanism
« Reply #3 on: August 13, 2019, 03:04:04 AM »
Lithium usually coordinates to the carbonyl oxygen and furhter activates it for the reduction. It plays some role because changing the counterions effects the reactivity of the reducing agent.

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