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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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 15
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.
Verified step by step guidance1
Step 1: Begin by identifying the functional groups involved in the reaction. Salicylic acid contains both a phenolic hydroxyl group (-OH) and a carboxylic acid group (-COOH). Acetic anhydride is a reactive compound with two acyl groups. The acid catalyst (sulfuric acid) will protonate key intermediates to facilitate the reaction.
Step 2: In the acid-catalyzed mechanism, sulfuric acid donates a proton (H⁺) to the carbonyl oxygen of acetic anhydride. This protonation increases the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack. Represent this step using MathML:
Step 3: The phenolic hydroxyl group (-OH) of salicylic acid acts as a nucleophile and attacks the electrophilic carbonyl carbon of the protonated acetic anhydride. This forms a tetrahedral intermediate. Represent the nucleophilic attack using MathML:
Step 4: The tetrahedral intermediate undergoes proton transfer and elimination of acetic acid (CH₃COOH), regenerating the acid catalyst (H⁺). This step completes the formation of acetylsalicylic acid (aspirin). Represent the elimination step using MathML:
Step 5: Sulfuric acid dramatically increases the reaction rate because it acts as a strong acid, effectively protonating the acetic anhydride and stabilizing intermediates. This lowers the activation energy of the reaction, making the process faster and more efficient.
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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 these reactions, the acid donates protons (H+) to the reactants, enhancing their electrophilicity and facilitating the formation of intermediates. This is particularly important in organic reactions where the presence of an acid can stabilize charged intermediates, making the overall process more efficient.
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Acid Catalyzed
Mechanism of Esterification
The mechanism of esterification describes how carboxylic acids react with alcohols or anhydrides to form esters. In the case of salicylic acid and acetic anhydride, the reaction involves the nucleophilic attack of the hydroxyl group of salicylic acid on the carbonyl carbon of acetic anhydride, leading to the formation of an ester bond and the release of acetic acid. Understanding this mechanism is crucial for predicting the products and reaction conditions.
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Role of Sulfuric Acid as a Catalyst
Sulfuric acid acts as a strong acid catalyst that significantly increases the reaction rate by providing protons to the reaction mixture. This protonation enhances the electrophilic character of the acetic anhydride, making it more reactive towards nucleophilic attack. The presence of sulfuric acid also helps to remove water formed during the reaction, shifting the equilibrium towards product formation and thus accelerating the overall reaction.
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Related Practice
Textbook Question
Suppose we have some optically pure (R)-2-butyl acetate that has been 'labeled' with the heavy 18O isotope at one oxygen atom as shown.
(c) Explain how you would prove experimentally where the 18O label appears in the products. (18O is not radioactive.)
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Textbook Question
Suppose we have some optically pure (R)-2-butyl acetate that has been "labeled" with the heavy 18O isotope at one oxygen atom as shown.
(b) Repeat part (a) for the acid-catalyzed hydrolysis of this compound.
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Textbook Question
Propose a mechanism for the acid-catalyzed hydrolysis of phenylalanine ethyl ester.
Textbook Question
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.
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Textbook Question
Suppose we have some optically pure (R)-2-butyl acetate that has been 'labeled' with the heavy 18O isotope at one oxygen atom as shown.
(a) Draw a mechanism for the hydrolysis of this compound under basic conditions. Predict which of the products will contain the 18O label. Also predict whether the butan-2-ol product will be pure (R), pure (S), or racemized.
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