December 12, 2019, 06:36:01 AM
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Topic: Aminolysis ester: mechanism  (Read 198 times)

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Offline xshadow

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Aminolysis ester: mechanism
« on: November 21, 2019, 10:49:01 AM »
I have some doubts about aminolysis of ester

https://i.imgur.com/tZFVF21.jpg


First of all ...which will be the intermediate in this  reaction condition(NH3 -basic reagent) ?? (A,B or C)

I use NH3 so I suppose to be in basic condition

If pH>pkNH4 +(9.4) and pKROH (16)I'll have  the  prevalence of the intermediate with the conjugated bases

But anyway - NHR  is a poor leaving group compared to  --OCH2CH3...90% of time tje leaving group will be  the amino one

So how can I get the amide product?
Thanks!!

Offline hollytara

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Re: Aminolysis ester: mechanism
« Reply #1 on: November 21, 2019, 11:09:31 AM »
So A will be initial intermediate of nucleophilic attack of RNH2 on carbonyl.

But alkoxide is strong enough base to take H+ from protonated amine - this gives B.

Since you are in basic conditions with excess of amine, a small amount of C will be formed - even if only a fraction of a percent, if it reacts to give product the reaction will proceed.

Alkoxide is much better leaving group than amide (RNH- anion).

Offline xshadow

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Re: Aminolysis ester: mechanism
« Reply #2 on: November 25, 2019, 06:59:48 AM »
So A will be initial intermediate of nucleophilic attack of RNH2 on carbonyl.

But alkoxide is strong enough base to take H+ from protonated amine - this gives B.

Since you are in basic conditions with excess of amine, a small amount of C will be formed - even if only a fraction of a percent, if it reacts to give product the reaction will proceed.

Alkoxide is much better leaving group than amide (RNH- anion).

Thanksss! :)

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