Textbook Question
b. Explain why the rate of aminolysis of an ester cannot be increased by H+.
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Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 15 - Reactions of Carboxylic Acids and Carboxylic Acid DerivativesProblem 28b(ii)
Bruice 8th EditionCh. 15 - Reactions of Carboxylic Acids and Carboxylic Acid DerivativesProblem 28b(ii)Chapter 16, Problem 28b(ii)
b. Explain why the rate of aminolysis of an ester cannot be increased by HO−, or RO−.
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The aminolysis of an ester involves the reaction of an ester with an amine to form an amide and an alcohol. This reaction proceeds via a nucleophilic acyl substitution mechanism.
In the mechanism, the amine acts as the nucleophile, attacking the carbonyl carbon of the ester. The carbonyl carbon is electrophilic due to the partial positive charge caused by the electronegativity of the oxygen atom in the carbonyl group.
Adding HO⁻ (hydroxide ion) or RO⁻ (alkoxide ion) does not increase the rate of aminolysis because these species are stronger nucleophiles than the amine. If present, they would compete with the amine for the carbonyl carbon, leading to hydrolysis or transesterification instead of aminolysis.
Additionally, the reaction environment for aminolysis is typically neutral or slightly basic to avoid deprotonating the amine. If the solution becomes too basic due to the presence of HO⁻ or RO⁻, the amine may be deprotonated to form an amide ion (RNH⁻), which is a much weaker nucleophile and would slow down the reaction.
Thus, the rate of aminolysis cannot be increased by HO⁻ or RO⁻ because these bases either compete with the amine or alter the reaction conditions in a way that hinders the nucleophilic attack by the amine.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aminolysis of Esters
Aminolysis is a nucleophilic substitution reaction where an amine reacts with an ester to form an amide and an alcohol. In this process, the nucleophile (amine) attacks the carbonyl carbon of the ester, leading to the displacement of the leaving group. Understanding the mechanism of this reaction is crucial to analyze how different nucleophiles affect the reaction rate.
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02:39
Ester Nomenclature
Nucleophilicity
Nucleophilicity refers to the strength of a nucleophile in donating an electron pair to form a new bond. In the context of aminolysis, the nucleophile's ability to attack the electrophilic carbonyl carbon of the ester is essential. Hydroxide (HO−) and alkoxide (RO−) ions are strong nucleophiles, but their basicity can lead to competing reactions, which can affect the overall reaction rate.
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08:27Nucleophilic Addition
Basicity vs. Nucleophilicity
Basicity is the tendency of a species to accept protons, while nucleophilicity is its ability to donate electron pairs. In the case of HO− and RO−, their strong basicity can lead to deprotonation of the amine, reducing the effective concentration of the nucleophile needed for aminolysis. This competition between basicity and nucleophilicity explains why increasing the concentration of these bases does not enhance the rate of aminolysis.
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06:21Understanding the difference between basicity and nucleophilicity.
Related Practice
Textbook Question
Propose a mechanism for the following reaction. (Hint: Number the carbons to help you see where they end up in the product.)
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Textbook Question
Write the mechanism for the acid-catalyzed transesterification of ethyl acetate with methanol.
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Textbook Question
Write the mechanism for the acid-catalyzed reaction of tert-butyl acetate with methanol.
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Textbook Question
Show how each of the following esters could be prepared using a carboxylic acid as one of the starting materials:
a. methyl butyrate (odor of apples)
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Textbook Question
D. N. Kursanov, a Russian chemist, proved that the bond that is broken in the hydroxide-ion-promoted hydrolysis of an ester is the acyl C—O bond, rather than the alkyl C—O bond, by studying the hydrolysis of the following ester under basic conditions:
a. What products contained the 18O label?
b. What product would have contained the 18O label if the alkyl C—O bond had broken?
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