Textbook Question
Propose a mechanism for the reaction of benzyl alcohol with acetyl chloride to give benzyl acetate.
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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 6b
Propose a mechanism for the reaction of benzoic acid with acetyl chloride to give acetic benzoic anhydride.
Verified step by step guidance1
Step 1: Identify the reactants and the product. The reactants are benzoic acid (C₆H₅COOH) and acetyl chloride (CH₃COCl), and the product is acetic benzoic anhydride (C₆H₅COOCOCH₃). This is an acylation reaction where an acid chloride reacts with a carboxylic acid to form an anhydride.
Step 2: Recognize the role of acetyl chloride as an electrophile. The carbonyl carbon in acetyl chloride is highly electrophilic due to the electron-withdrawing effect of the chlorine atom. Benzoic acid acts as a nucleophile, with the oxygen atom of the hydroxyl group attacking the electrophilic carbonyl carbon of acetyl chloride.
Step 3: Describe the nucleophilic attack. The lone pair of electrons on the oxygen atom of the hydroxyl group in benzoic acid attacks the carbonyl carbon of acetyl chloride, forming a tetrahedral intermediate. This intermediate is unstable and will collapse to eliminate a leaving group.
Step 4: Explain the elimination of the leaving group. The tetrahedral intermediate collapses, expelling the chloride ion (Cl⁻) as the leaving group. This results in the formation of a mixed anhydride intermediate, where the benzoic acid and acetyl groups are connected.
Step 5: Finalize the mechanism. The mixed anhydride intermediate stabilizes to form acetic benzoic anhydride, completing the reaction. The product contains two carbonyl groups connected by an oxygen atom, characteristic of an anhydride.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Reactions
In organic chemistry, acid-base reactions involve the transfer of protons (H+) between molecules. In the context of the reaction between benzoic acid and acetyl chloride, benzoic acid acts as a Brønsted acid, donating a proton to the acetyl chloride, which is a reactive acyl chloride. This step is crucial for initiating the formation of the anhydride product.
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The Lewis definition of acids and bases.
Nucleophilic Acyl Substitution
Nucleophilic acyl substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an acyl compound, leading to the substitution of a leaving group. In this case, the hydroxyl group from benzoic acid acts as a nucleophile, attacking the carbonyl carbon of acetyl chloride, facilitating the formation of the acetic benzoic anhydride.
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Formation of Anhydrides
Anhydrides are formed through the condensation of two carboxylic acids or a carboxylic acid and an acyl chloride, resulting in the loss of water. The reaction between benzoic acid and acetyl chloride exemplifies this process, where the hydroxyl group from benzoic acid and the chloride from acetyl chloride are eliminated, yielding acetic benzoic anhydride as the product.
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Related Practice
Textbook Question
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?
Textbook Question
Propose a mechanism for the reaction of aniline with acetic anhydride to give acetanilide.
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Textbook Question
Name the following carboxylic acid derivatives, giving both a common name and an IUPAC name where possible.
(o)
(p)
Textbook Question
Name the following carboxylic acid derivatives, giving both a common name and an IUPAC name where possible.
(q)
(r)
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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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