Textbook Question
Show how the following ketones might be synthesized from the indicated acids, using any necessary reagents.
(a) propiophenone from propionic acid (using Friedel–Crafts acylation)
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Ch. 21 - Carboxylic Acid Derivatives
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 21, Problem 20b
Propose a mechanism for the hydrolysis of N,N-dimethylacetamide
(b) under acidic conditions.
Verified step by step guidance1
Step 1: Protonation of the carbonyl oxygen - Under acidic conditions, the lone pair of electrons on the oxygen atom of the carbonyl group in N,N-dimethylacetamide will interact with a proton (H⁺) from the acid, leading to the formation of a protonated carbonyl group. This increases the electrophilicity of the carbonyl carbon.
Step 2: Nucleophilic attack by water - The water molecule acts as a nucleophile and attacks the electrophilic carbonyl carbon, forming a tetrahedral intermediate. This step involves the addition of water to the carbonyl group.
Step 3: Proton transfer - A proton transfer occurs within the tetrahedral intermediate to stabilize the structure. This step involves the movement of a proton from the water molecule to the nitrogen atom, making the leaving group more favorable.
Step 4: Cleavage of the C-N bond - The nitrogen atom, now protonated, becomes a good leaving group. The C-N bond breaks, leading to the formation of acetic acid and a protonated amine (N,N-dimethylamine).
Step 5: Deprotonation - The protonated amine loses a proton to regenerate the neutral amine (N,N-dimethylamine), and the acetic acid remains as the final product of the hydrolysis reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydrolysis Mechanism
Hydrolysis is a chemical reaction involving the breaking of a bond in a molecule using water. In the case of N,N-dimethylacetamide, the mechanism typically involves the nucleophilic attack of water on the carbonyl carbon, leading to the formation of a tetrahedral intermediate. This intermediate can then collapse, resulting in the formation of acetic acid and dimethylamine.
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Acidic Conditions
Acidic conditions refer to an environment where the pH is less than 7, often achieved by adding a strong acid like HCl. In hydrolysis reactions, acids can protonate the carbonyl oxygen, increasing the electrophilicity of the carbonyl carbon. This makes it more susceptible to nucleophilic attack by water, facilitating the hydrolysis process.
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Nucleophilicity
Nucleophilicity is a measure of how readily a nucleophile donates an electron pair to form a chemical bond. In the hydrolysis of N,N-dimethylacetamide, water acts as a nucleophile. The presence of acidic conditions enhances the nucleophilicity of water by stabilizing the transition state, thus promoting the reaction with the electrophilic carbonyl carbon.
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Related Practice
Textbook Question
In which step(s) of the hydride reduction of an ester does the compound undergo reduction? (Hint: Count the bonds to oxygen.)
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Textbook Question
Draw the important resonance contributors for both resonance-stabilized cations (in brackets) in the mechanism for acid-catalyzed hydrolysis of an amide.
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Textbook Question
Propose a mechanism for the hydrolysis of N,N-dimethylacetamide
(a) under basic conditions.
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Textbook Question
The mechanism for acidic hydrolysis of a nitrile resembles the basic hydrolysis, except that the nitrile is first protonated, activating it toward attack by a weak nucleophile (water). Under acidic conditions, the proton transfer (tautomerism) involves protonation on nitrogen followed by deprotonation on oxygen. Propose a mechanism for the acid-catalyzed hydrolysis of benzonitrile to benzamide.
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Textbook Question
Propose a mechanism for the basic hydrolysis of benzonitrile to the benzoate ion and ammonia.
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