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Question

What happens when ethylamine is made to react with excess formic acid and formaldehyde?
 
  1. The mechanism involves reductive amination
  2. The intermediate is a secondary amine
  3. The final product is a tertiary amine
  4. This reaction is called Eschweiler-Clarke methylation


Solution

The correct option is D This reaction is called Eschweiler-Clarke methylation
In the first step, the excess formaldehyde and the primary amine react to give the imine:

Don’t forget, this reaction does happen in the presence of an acid – just like any imine formation. The next step is where the reductive amination happens; but before that, the acid protonates the imine into an iminium. Note how the formate anion acts as a hydride donor!!

But since there is excess HCHO in the flask, the secondary amine will be methylated via an iminium once again to finally yield a tertiary amine. The tertiary amine cannot form an imine and the reaction stops here:

This reaction is called the Eschweiler-Clarke methylation or Eschweiler-Clarke synthesis.
 

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