Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds

Problem 8c

Chapter 22, Problem 8c

Give the expected products of the following acid-catalyzed reactions.
(c) cyclohexanone + aniline

Verified step by step guidance

Step 1: Recognize that the reaction involves cyclohexanone (a ketone) and aniline (an amine) under acid-catalyzed conditions. This is a classic example of imine formation, where a ketone reacts with a primary amine to form an imine (Schiff base).

Step 2: Under acidic conditions, the carbonyl group of cyclohexanone is protonated, increasing the electrophilicity of the carbonyl carbon. This makes it more susceptible to nucleophilic attack by the lone pair on the nitrogen atom of aniline.

Step 3: The nucleophilic nitrogen of aniline attacks the electrophilic carbonyl carbon of cyclohexanone, forming a tetrahedral intermediate. This intermediate contains both the amine group and the hydroxyl group attached to the same carbon.

Step 4: The tetrahedral intermediate undergoes dehydration (loss of water) under acidic conditions. This step involves the protonation of the hydroxyl group, followed by its elimination as water, leading to the formation of a double bond between the carbon and nitrogen atoms.

Step 5: The final product is an imine, specifically N-phenylcyclohexanimine, where the nitrogen of aniline is double-bonded to the carbon of the former carbonyl group in cyclohexanone. This imine is stabilized under the reaction conditions.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid-Catalyzed Reactions

Acid-catalyzed reactions involve the use of an acid to increase the rate of a chemical reaction. In organic chemistry, acids can protonate reactants, making them more electrophilic and facilitating nucleophilic attacks. This is particularly important in reactions involving carbonyl compounds, such as ketones and aldehydes, where the carbonyl carbon becomes more reactive in the presence of an acid.

Nucleophilic Addition to Carbonyls

Nucleophilic addition to carbonyls is a fundamental reaction in organic chemistry where a nucleophile attacks the electrophilic carbon of a carbonyl group (C=O). In the case of cyclohexanone reacting with aniline, the nitrogen atom of aniline acts as a nucleophile, attacking the carbonyl carbon of cyclohexanone, leading to the formation of an intermediate that can further react to yield the final product.

Formation of Imines

The reaction between a carbonyl compound and a primary amine, such as aniline, typically leads to the formation of an imine. This process involves the nucleophilic attack of the amine on the carbonyl carbon, followed by the elimination of water. The resulting imine is characterized by a C=N double bond and is an important functional group in organic synthesis, often used in further transformations.

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Related Practice

Textbook Question

Show how you would accomplish each conversion using an enamine synthesis with pyrrolidine as the secondary amine.

(a) cyclopentanone → 2-allylcyclopentanone

(b) pentan-3-one → 2-methyl-1-phenylpentan-3-one

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Textbook Question

Without looking back, propose a mechanism for the hydrolysis of this iminium salt to the alkylated ketone. The first step is attack by water, followed by loss of a proton to give a carbinolamine. Protonation on nitrogen allows pyrrolidine to leave, giving the protonated ketone.

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Textbook Question

Show how you would accomplish each conversion using an enamine synthesis with pyrrolidine as the secondary amine.

(c)

Textbook Question

Give the expected products of the following acid-catalyzed reactions.

(a) acetophenone + methylamine

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Textbook Question

Give the expected products of the following acid-catalyzed reactions.

(d) cyclohexanone + piperidine

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