Ch. 18 - Ketones and Aldehydes

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

Wade 9th Edition

Ch. 18 - Ketones and Aldehydes

Problem 20a

Chapter 18, Problem 20a

Propose a mechanism for the hydrolysis of benzaldehyde methyl imine just shown.

Verified step by step guidance

Step 1: Protonation of the imine nitrogen. The reaction begins with the addition of H3O+ (acidic conditions), which protonates the nitrogen atom of the imine group. This increases the electrophilicity of the carbon atom attached to the nitrogen.

Step 2: Nucleophilic attack by water. A water molecule acts as a nucleophile and attacks the electrophilic carbon atom of the imine group, forming a tetrahedral intermediate.

Step 3: Proton transfer. A proton transfer occurs within the intermediate to stabilize the structure, leading to the formation of a hydroxyl group (-OH) and a positively charged nitrogen group.

Step 4: Cleavage of the C-N bond. The positively charged nitrogen group is eliminated as CH3NH2 (methylamine), leaving behind a carbonyl group (-C=O) on the benzaldehyde structure.

Step 5: Deprotonation. The hydroxyl group is deprotonated to regenerate the neutral carbonyl compound, resulting in the final products: benzaldehyde and methylamine.

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Key Concepts

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

Imine Hydrolysis

Imine hydrolysis is a chemical reaction where an imine reacts with water, often in the presence of an acid or base, to form a carbonyl compound and an amine. In this case, benzaldehyde methyl imine undergoes hydrolysis to yield benzaldehyde and methylamine. Understanding this process is crucial for predicting the products and mechanism of the reaction.

Acid-Base Catalysis

Acid-base catalysis involves the use of an acid or base to accelerate a chemical reaction. In the hydrolysis of imines, hydronium ions (H3O+) act as a catalyst, facilitating the protonation of the imine nitrogen, which enhances the electrophilicity of the carbon atom. This step is essential for the subsequent nucleophilic attack by water.

Nucleophilic Attack

Nucleophilic attack is a fundamental concept in organic chemistry where a nucleophile, a species with a pair of electrons, attacks an electrophile, a positively charged or electron-deficient species. In the hydrolysis of benzaldehyde methyl imine, water acts as the nucleophile that attacks the carbon atom of the imine, leading to the formation of the carbonyl compound and the release of the amine.

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Related Practice

Textbook Question

Give the structures of the carbonyl compound and the amine used to form the following imines.

(d)

(e)

(f)

Predict the products of the following reactions.

(a)

(b)

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Textbook Question

Predict the products of the following reactions.

(c)

(d)

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Textbook Question

Show how hex-1-yne might be converted to

d. 1,1,2,2-tetrabromohexane.

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Textbook Question

Give the structures of the carbonyl compound and the amine used to form the following imines.

(a)

(b)

(c)

1722

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Textbook Question

2,4-Dinitrophenylhydrazine is frequently used for making derivatives of ketones and aldehydes because the products (2,4-dinitrophenylhydrazones, called 2,4-DNP derivatives) are even more likely than the phenylhydrazones to be solids with sharp melting points. Propose a mechanism for the reaction of acetone with 2,4-dinitrophenylhydrazine in a mildly acidic solution.

937

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