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Organic Chemistry: Imine Formation and Hydrolysis

organic-chemistry-imine-formation-and-hydrolysis

An imine is a chemical compound with a carbon-nitrogen double bond where the nitrogen is also bonded to a hydrogen or a carbon chain (R can stand for either in this case). It can be formed from a ketone or an aldehyde reacted with ammonia or a primary amine in acid. The reaction is also reversable. I will show the step-by-step mechanism of both the formation and the hydrolysis.

Formation

I will use a simple ketone as an example. This could also be a ketone of varying carbon chain length substituents or an aldehyde.

organic-chemistry-imine-formation-and-hydrolysis

1. First the carbonyl oxygen is protonated.

organic-chemistry-imine-formation-and-hydrolysis

2. There is a resonance form.

organic-chemistry-imine-formation-and-hydrolysis

3. The primary amine attacks the carbon with the positive charge. This results in a compound with a positive charge on the nitrogen.

organic-chemistry-imine-formation-and-hydrolysis

4. Another molecule of ketone will remove one of the hydrogens from the nitrogen. This results in a a tetrahedral intermediate, which in this case is known as a carbinolamine or a hemiaminal.

organic-chemistry-imine-formation-and-hydrolysis

5. The oxygen is protonated once again, forming a good leaving group (the +OH2).

organic-chemistry-imine-formation-and-hydrolysis

6. The leaving group leaves, resulting in a positive charge on the central carbon.

organic-chemistry-imine-formation-and-hydrolysis

7. There is a resonance form.

organic-chemistry-imine-formation-and-hydrolysis

8. Another molecule of ketone deprotonates the nitrogen. This results in the imine.

Full Mechanism

organic-chemistry-imine-formation-and-hydrolysis
organic-chemistry-imine-formation-and-hydrolysis

Hydrolysis

Now I will show the hydrolysis of an imine in H3O+ and heat. The mechanism is basically the same as the formation but in reverse.

organic-chemistry-imine-formation-and-hydrolysis

1. First the nitrogen is protonated.

organic-chemistry-imine-formation-and-hydrolysis

2. There is a resonance form.

organic-chemistry-imine-formation-and-hydrolysis

3. A water molecule attacks the postively charged central carbon.

organic-chemistry-imine-formation-and-hydrolysis

4. Another water molecule deprotonates the oxygen, resulting in a tetrahedral intermediate.

organic-chemistry-imine-formation-and-hydrolysis

5. The nitrogen is protonated, forming a leaving group.

organic-chemistry-imine-formation-and-hydrolysis

6. The leaving group leaves, resulting in a positive charge on the central carbon.

organic-chemistry-imine-formation-and-hydrolysis

7. There is a resonance form.

organic-chemistry-imine-formation-and-hydrolysis

8. A water molecule deprotonates the oxygen. This results in the ketone.

Full Mechanism

organic-chemistry-imine-formation-and-hydrolysis

Comments

Siddhant on August 26, 2018:

Hi, what if the R group attached to nitrogen in imine is t-Bu group. So, how you will do its hydrolysis? I already tried 1M HCl and p-TsOH.H2O, but it did not work. Thanks!

kanaparthi sunny from Hyderabad, Andhra Pradesh on July 20, 2014:

nice topic.

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