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19.8 Nucleophilic Addition of Amines: Imine and Enamine Formation

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    After completing this section, you should be able to

    1. write equations to describe the reactions that occur between aldehydes or ketones and primary or secondary amines.
    2. identify the product formed from the reaction of a given aldehyde or ketone with a given primary or secondary amine.
    3. identify the aldehyde or ketone, the amine, or both, required in the synthesis of a given imine or enamine.
    4. write the detailed mechanism for the reaction of an aldehyde or ketone with a primary amine.
    5. write the detailed mechanism for the reaction of an aldehyde or ketone with a secondary amine.
    6. explain why the rate of a reaction between an aldehyde or ketone and a primary or secondary amine is dependent on pH.
    Key Terms

    Make certain that you can define, and use in context, the key terms below.

    • 2,4‑dinitrophenylhydrozone
    • enamine
    • imine
    Study Notes

    An imine is a compound that contains the structural unit

    An enamine is a compound that contains the structural unit


    Both of these types of compound can be prepared through the reaction of an aldehyde or ketone with an amine.

    You may have the opportunity to observe the reaction of an aldehyde and ketone with 2,4‑dinitrophenylhydrazine (Brady’s reagent) to form a 2,4‑dinitrophenylhydrozone in the laboratory. This is a classical organic chemistry test to confirm the presence of a carbonyl group. The reaction produces very colourful and bright precipitates of yellow, orange and red.

    If you can understand why the two reactions of imine and enamine formation are essentially identical, and can write a detailed mechanism for each one, you are well on the way to mastering organic chemistry. If you understand how and why these reactions occur, you can keep the amount of material that you need to memorize to a minimum.

    Reaction with Primary Amines to form Imines

    The reaction of aldehydes and ketones with ammonia or 1º-amines forms imine derivatives, also known as Schiff bases (compounds having a C=N function). Water is eliminated in the reaction.

    imine formation sample reaction.svg

    Predicting the Products of an Imine Forming Reaction

    During imine formation, the carbonyl oxygen is completely removed. The nitrogen of the 1o amine reactant replaces the carbonyl oxygen to form the imine C=N bond. During the process the nitrogen of the 1o amine loses both of its hydrogens.

    determining the product of an imine formation.svg

    Examples of Imine Forming Reactions

    imine formation example.svg

    imine formation example b.svg

    Mechanism of Imine Formation

    Imine formation is a reversible process that starts with the nucleophilic addition of a primary amine to the carbonyl group of an aldehyde or ketone. Next, a proton transfer forms a neutral amino alcohol called a carbinolamine. Acid protonation of the carbinolamine oxygen converts it into a better leaving group which is subsequently eliminated as water producing an iminium ion. Deprotonation of nitrogen gives the final imine product.

    1) Nucleophilic addition

    imine formation mechanims step 1.svg

    2) Protron transfer

    imine formation mechanims step 2.svg

    3) Protonation

    imine formation mechanims step 3.svg

    4) Water is eliminated to form an iminium ion.

    imine formation mechanims step 4.svg

    5) Deprotonation

    imine formation mechanims step 5.svg

    Reversibility of Imine Forming Reactions

    Imines can be hydrolyzed back to the corresponding 1o amine under acidic conditions.

    reversibility of imine formation.svg

    Reactions Involving other Reagents of the type Y-NH2

    A wide variety of substances with −NH2 groups can react with aldehydes and ketones by an addition-elimination sequence to yield compounds with a carbon-nitrogen double bond. Imines are sometimes difficult to isolate and purify due to their sensitivity to hydrolysis. Consequently, other reagents of the type Y–NH2 have been studied, and found to give stable products (R2C=N–Y) useful in characterizing the aldehydes and ketones from which they are prepared. Some of these reagents are listed below, together with the structures and names of their carbonyl reaction products. Hydrazones are used as part of the Wolff-Kishner reduction and will be discussed in more detail in Section 19.9.

    With the exception of unsubstituted hydrazones, these derivatives are easily prepared and are often crystalline solids - even when the parent aldehyde or ketone is a liquid. Since melting points can be determined more quickly and precisely than boiling points, derivatives such as these are useful for comparison and identification of carbonyl compounds. It should be noted that although semicarbazide has three nitrogen groups (–NH2) only one of them is a reactive amine. The other two are similar to amides and are deactivated by resonance with the adjacent carbonyl group.

    reaction involving other reagents.svg


    Cinnamaldehyde Reacting with Hydroxyl Amine to form Cinnamaldehyde Oxime.svg

    Cinnamaldehyde reacting with hydroxylamine to form cinnamaldehyde oxime

    Acetone Reacting with Semicarbazide to form Acetone Semicarbazide.svg

    Acetone reacting with semicarbazide to form acetone semicarbazide

    Reaction with Secondary Amines to form Enamines

    Most aldehydes and ketones react with 2º-amines to give products known as enamines. It should be noted that, like acetal formation, these are acid-catalyzed reversible reactions in which water is lost. Consequently, enamines are easily converted back to their carbonyl precursors by acid-catalyzed hydrolysis.

    Equilibrium reaction diagram. A secondary amine reacts with an aldehyde or ketone and hydronium forming an enamine.


    1) Nuleophilic attack

    2) Proton transfer

    3) Protonation of OH

    4) Removal of water

    5) Deprotonation

    Reversibility of Enamines


    Exercise 19.8.1

    Please draw the products of the following reactions.

    question 1 structures.svg












      answer 1 structures.svg

    Exercise 19.8.2

    Please draw the structure of the reactant needed to produce the indicated product.

    question 2 structures.svg













    answer 2 structures.svg




    Exercise 19.8.3

    Please draw the products of the following reaction.

    question 3 structures.svg


     answer 3 structures.svg

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    19.8 Nucleophilic Addition of Amines: Imine and Enamine Formation is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.