Textbook Question
Show how the following ketones might be synthesized from the indicated acids, using any necessary reagents.
(a) propiophenone from propionic acid (using alkylation of the acid)
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Ch. 20 - Carboxylic Acids
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 20, Problem 23a
Propose mechanisms for the nucleophilic acyl substitutions to form ethyl benzoate as shown on the previous page.
Verified step by step guidance1
Step 1: Identify the reactants and products. The reactant is benzoyl chloride (PhCOCl), and the product is ethyl benzoate (PhCOOCH3). The reaction involves nucleophilic acyl substitution, where the chlorine atom is replaced by a methoxy group (-OCH3).
Step 2: Recognize the role of pyridine. Pyridine acts as a base to neutralize the HCl formed during the reaction, preventing the reaction medium from becoming too acidic and facilitating the substitution process.
Step 3: Initiate the mechanism. Methanol (CH3OH) acts as the nucleophile. The lone pair of electrons on the oxygen atom of methanol attacks the carbonyl carbon of benzoyl chloride, forming a tetrahedral intermediate. This step is driven by the electrophilic nature of the carbonyl carbon due to the electron-withdrawing effect of the chlorine atom.
Step 4: Collapse of the tetrahedral intermediate. The tetrahedral intermediate undergoes rearrangement, where the chlorine atom is expelled as a leaving group. This results in the formation of the ester bond (PhCOOCH3).
Step 5: Neutralization by pyridine. Pyridine reacts with the HCl generated during the substitution, forming pyridinium chloride. This prevents the accumulation of HCl and stabilizes the reaction environment.
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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 in organic chemistry where a nucleophile attacks the carbonyl carbon of an acyl compound, leading to the replacement of a leaving group. This mechanism typically involves the formation of a tetrahedral intermediate, which then collapses to regenerate the carbonyl and expel the leaving group. Understanding this process is crucial for predicting the products of reactions involving acyl compounds.
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Nucleophiles and Electrophiles can react in Substitution Reactions.
Role of Pyridine
Pyridine is often used as a base and a catalyst in nucleophilic acyl substitution reactions. It can deprotonate the nucleophile, enhancing its nucleophilicity, and stabilize the tetrahedral intermediate formed during the reaction. Additionally, pyridine can help facilitate the departure of the leaving group, making the reaction more efficient. Recognizing the role of pyridine is essential for understanding the mechanism of the reaction leading to ethyl benzoate.
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Formation of Ethyl Benzoate
Ethyl benzoate is an ester formed from the reaction of benzoic acid and ethanol, typically through nucleophilic acyl substitution. In this context, the reaction involves the nucleophilic attack of the ethoxide ion (from ethanol) on the carbonyl carbon of the acyl chloride, leading to the formation of the ester bond. Understanding the specific steps and intermediates in this transformation is key to proposing a detailed mechanism for the synthesis of ethyl benzoate.
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Related Practice
Textbook Question
Show how the following ketones might be synthesized from the indicated acids, using any necessary reagents.
(b) methyl cyclohexyl ketone from cyclohexanecarboxylic acid
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Textbook Question
Show how you would use an acid chloride as an intermediate to synthesize
(b) phenyl propionate (CH3CH2COOPh) from propionic acid and phenol.
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Textbook Question
Propose mechanisms for the nucleophilic acyl substitutions to form N-methylacetamide as shown on the previous page.
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Textbook Question
Propose a mechanism for the reaction of benzoic acid with oxalyl chloride. This mechanism begins like the thionyl chloride reaction, to give a reactive mixed anhydride. Nucleophilic acyl substitution by chloride ion gives a tetrahedral intermediate that eliminates a leaving group, which then fragments into carbon dioxide, carbon monoxide, and chloride ion.
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Textbook Question
Show how you would use an acid chloride as an intermediate to synthesize.
(a) N-phenylbenzamide (PhCONHPh) from benzoic acid and aniline.
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