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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: xshadow on November 21, 2019, 10:49:01 AM

Title: Aminolysis ester: mechanism
Post by: xshadow on November 21, 2019, 10:49:01 AM

I have some doubts about aminolysis of ester

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

Title: Re: Aminolysis ester: mechanism
Post by: hollytara 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).

Title: Re: Aminolysis ester: mechanism
Post by: xshadow on November 25, 2019, 06:59:48 AM

Quote from: hollytara 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).

Thanksss! :)