Textbook Question
Show how you would use acetic anhydride and an appropriate alcohol or amine to synthesize (i) benzyl acetate and (ii) N,N-diethylacetamide.
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 13
Acid-catalyzed transesterification:
Complete the mechanism for this acid-catalyzed transesterification by drawing out all the individual steps. Draw the important resonance contributors for each resonance-stabilized intermediate.
Verified step by step guidance1
Step 1: Protonation of the carbonyl oxygen. The acid catalyst (H⁺) donates a proton to the oxygen atom of the carbonyl group, increasing the electrophilicity of the carbonyl carbon. This step makes the carbonyl carbon more susceptible to nucleophilic attack.
Step 2: Nucleophilic attack by methanol (CH₃OH). The lone pair of electrons on the oxygen atom of methanol attacks the carbonyl carbon, forming a tetrahedral intermediate. This intermediate contains both the original ester group and the newly added methanol group.
Step 3: Proton transfer within the intermediate. A proton is transferred from the methanol group to the original ester oxygen, stabilizing the intermediate and preparing it for the next step. This step may involve resonance stabilization of the intermediate.
Step 4: Elimination of the leaving group. The ethoxy group (CH₂CH₃O⁻) is eliminated as the leaving group, forming ethanol (CH₃CH₂OH). This step restores the carbonyl group and completes the transesterification process.
Step 5: Deprotonation of the carbonyl oxygen. The protonated carbonyl oxygen loses a proton, regenerating the acid catalyst (H⁺) and yielding the final product, methyl benzoate (C₆H₅COOCH₃).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Transesterification
Transesterification is a chemical reaction where an ester is converted into another ester through the exchange of the alkoxy group. This process typically involves the reaction of an alcohol with an ester in the presence of an acid catalyst, which enhances the reaction rate. Understanding this concept is crucial for analyzing the mechanism, as it outlines the fundamental transformation occurring in the reaction.
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General Reaction
Acid Catalysis
Acid catalysis involves the use of an acid to increase the rate of a chemical reaction by providing protons (H+) to reactants. In the context of transesterification, the acid catalyst protonates the carbonyl oxygen of the ester, making it more electrophilic and susceptible to nucleophilic attack by the alcohol. This concept is essential for understanding how the reaction proceeds and the role of the catalyst in stabilizing intermediates.
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Resonance Stabilization
Resonance stabilization refers to the delocalization of electrons in a molecule, which can occur when multiple valid Lewis structures (resonance contributors) can be drawn. In the context of the transesterification mechanism, resonance stabilization of intermediates helps to lower the energy of these species, making them more stable and facilitating the reaction. Recognizing the resonance contributors is vital for accurately depicting the mechanism and understanding the stability of intermediates.
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Related Practice
Textbook Question
Propose a mechanism for the following ring-opening transesterification. Use the mechanism in Problem 21-13 as a model.
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Textbook Question
Propose a mechanism for the reaction of benzyl acetate with methylamine. Label the attacking nucleophile and the leaving group, and draw the transition state in which the leaving group leaves.
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Textbook Question
When ethyl 4-hydroxybutyrate is heated in the presence of a trace of a basic catalyst (sodium acetate), one of the products is a lactone. Propose a mechanism for formation of this lactone.
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Textbook Question
Propose a mechanism for the acid-catalyzed hydrolysis of phenylalanine ethyl ester.
Textbook Question
1. Propose a mechanism for the acid-catalyzed reaction of salicylic acid with acetic anhydride.
2. Explain why a single drop of sulfuric acid dramatically increases the reaction rate.
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