Textbook Question
Which of the following proposed reactions would take place quickly under mild conditions?
(a)
(b)
(c)
(d)
(e)
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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 6e
Propose a mechanism for the reaction of aniline with ethyl acetate to give acetanilide. What is the leaving group in your proposed mechanism? Would this be a suitable leaving group for an SN2 reaction?
Verified step by step guidance1
Step 1: Understand the reaction. Aniline (C₆H₅NH₂) reacts with ethyl acetate (CH₃COOCH₂CH₃) to form acetanilide (C₆H₅NHCOCH₃). This is an example of a nucleophilic acyl substitution reaction, where the nucleophile (aniline) attacks the carbonyl carbon of ethyl acetate.
Step 2: Propose the first step of the mechanism. The lone pair of electrons on the nitrogen atom of aniline attacks the electrophilic carbonyl carbon of ethyl acetate. This forms a tetrahedral intermediate, where the carbonyl oxygen becomes negatively charged.
Step 3: Identify the leaving group. In the tetrahedral intermediate, the ethoxy group (-OCH₂CH₃) is a good leaving group. The negatively charged oxygen reforms the carbonyl bond, expelling the ethoxy group as ethanol (CH₃CH₂OH).
Step 4: Analyze the leaving group for SN2 suitability. The ethoxy group (-OCH₂CH₃) is not a suitable leaving group for an SN2 reaction because it is a strong base and does not leave easily under SN2 conditions. SN2 reactions typically require weak bases as leaving groups, such as halides (e.g., Cl⁻, Br⁻, I⁻).
Step 5: Conclude the mechanism. The final product, acetanilide, is formed after the ethoxy group leaves and the carbonyl bond is reformed. The reaction proceeds via nucleophilic acyl substitution, not an SN2 mechanism, due to the nature of the leaving group and the reaction conditions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Acyl Substitution
Nucleophilic acyl substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an electrophilic carbonyl carbon, leading to the substitution of a leaving group. In the case of aniline reacting with ethyl acetate, the amine acts as the nucleophile, attacking the carbonyl carbon of the ester, resulting in the formation of acetanilide and the release of an acetate ion as the leaving group.
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Nucleophiles and Electrophiles can react in Substitution Reactions.
Leaving Groups
A leaving group is an atom or group that can depart with a pair of electrons in a chemical reaction, facilitating the formation of a new bond. In the proposed mechanism, the acetate ion (derived from ethyl acetate) serves as the leaving group. Good leaving groups are typically stable after departure, and acetate is considered a moderate leaving group due to its ability to stabilize the negative charge.
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SN2 Reaction Mechanism
The SN2 (substitution nucleophilic bimolecular) mechanism involves a single concerted step where a nucleophile attacks an electrophile, leading to the simultaneous displacement of a leaving group. For a leaving group to be suitable for an SN2 reaction, it must be able to stabilize the transition state and depart easily. While acetate is a reasonable leaving group for many reactions, it is not ideal for SN2 due to steric hindrance and the nature of the substrate involved.
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Related Practice
Textbook Question
Show how you would synthesize the following esters from appropriate acyl chlorides and alcohols.
(c) benzyl benzoate
(d) cyclopropyl cyclohexanecarboxylate
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Textbook Question
Propose a mechanism for the reaction of aniline with acetic anhydride to give acetanilide.
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Textbook Question
Show how you would synthesize the following esters from appropriate acyl chlorides and alcohols.
(a) ethyl propionate
(b) phenyl 3-methylhexanoate
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Textbook Question
Propose a mechanism for the reaction of benzoic acid with acetyl chloride to give acetic benzoic anhydride.
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Textbook Question
Propose a second mechanism for the reaction of benzoic acid with acetyl chloride to give acetic benzoic anhydride. This time, let the other oxygen of benzoic acid serve as the nucleophile to attack the carbonyl group of acetyl chloride. Because proton transfers are fast between these oxygen atoms, it is difficult to differentiate between these two mechanisms experimentally.
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