Question

Reaction of cyclohexanone with dimethylamine in the presence of catalytic amount of an acid forms a compound if water during the reaction is continuously removed. The compound formed is generally known as (1) an amine (2) an imine (3) an enamine (4) a Schiff's base

Short answer

an enamine

Step-by-step solution

Identify the reacting compounds

The reacting compounds are cyclohexanone and dimethylamine.

Determine the role of the acid catalyst

The acid catalyst is used to facilitate the reaction between cyclohexanone and dimethylamine. It helps in the removal of water during the reaction.

Analyze the reaction mechanism

Cyclohexanone reacts with dimethylamine in the presence of an acid catalyst. The oxygen of cyclohexanone is protonated by the acid, making the carbonyl carbon more electrophilic and susceptible to nucleophilic attack by the amine.

Describe the intermediate formed

An intermediate carbinolamine is formed initially, which then loses water to form a more stable compound.

Final product formation

The loss of water from the carbinolamine intermediate typically leads to the formation of an enamine, as the nitrogen atom of the amine forms a double bond with the carbon of the former carbonyl group and a single bond with an adjacent carbon atom.

Conclusion

The compound formed from the reaction of cyclohexanone with dimethylamine in the presence of an acid catalyst, with continuous removal of water, is generally known as an enamine.

Key concepts

Cyclohexanone Reaction

Cyclohexanone is a common organic molecule with a six-membered ring and a ketone functional group (C=O). When discussing the reaction of cyclohexanone, it’s important to note that the key point is the electrophilic nature of the carbonyl carbon. In organic chemistry, particularly in the context of IIT JEE Main, reactions involving cyclohexanone often explore how it interacts with various nucleophiles.
When cyclohexanone reacts with other substances like amines, the oxygen in the carbonyl group can be protonated, making the carbon even more electrophilic. This makes it easier for nucleophiles, such as amines, to attack the carbon. Understanding this reaction pathway is critical for grasping more complex reactions in organic chemistry.

Dimethylamine Reaction

Dimethylamine is an organic compound with the formula (CH₃)₂NH. It features a nitrogen atom bonded to two methyl groups and one hydrogen. As a nucleophile, dimethylamine can donate a pair of electrons to form a bond with electrophilic carbon atoms.
In our specific reaction, dimethylamine reacts with cyclohexanone. The nitrogen in dimethylamine provides the lone pair of electrons to the carbonyl carbon of cyclohexanone, especially when the carbonyl is made more electrophilic by protonation. This nucleophilic attack is the first step in forming an intermediate carbinolamine.

Enamine Formation

An enamine is a compound derived from an aldehyde or ketone and a secondary amine. The enamine formation reaction involves a critical intermediate: the carbinolamine (a compound with both a hydroxyl group and an amine group attached to the same carbon). Initially, the nucleophilic nitrogen of dimethylamine attacks the electrophilic carbonyl carbon of cyclohexanone, leading to this intermediate.
The carbinolamine intermediate then undergoes dehydration, losing a water molecule, which results in the formation of an enamine. The nitrogen atom forms a double bond with the carbon and a single bond with an adjacent carbon atom in the final structure. This structural change is key in many organic reactions and offers better reactivity in subsequent reactions.

Acid Catalyst Mechanism

Understanding the role of an acid catalyst in organic reactions is crucial. An acid catalyst can provide protons (H⁺ ions) that increase the electrophilicity of certain atoms. In the reaction between cyclohexanone and dimethylamine, the acid catalyst protonates the oxygen in the carbonyl group of cyclohexanone. This increases the electrophilicity of the carbon, making it more susceptible to nucleophilic attack by the amine.
The acid catalyst doesn't get consumed in this reaction; it merely facilitates the process by making it easier for the reactants to interact. As the reaction progresses, the intermediate formed sheds a water molecule to yield an enamine. Understanding this mechanism is key for mastering various organic reactions, as it reveals how catalysts can accelerate complex transformations.