Textbook Question
Propose mechanisms for the following reactions.
(a)
(b)
22. Carboxylic Acid Derivatives: NAS
Acid-Catalyzed Ester Hydrolysis
4:28 minutesProblem 17b
Textbook Question
(b) Finish the solution for Solved Problem 20-1 by providing a mechanism for the acid-catalyzed hydrolysis of ethyl formate.
Verified step by step guidance1
Identify the reaction type: The problem involves the acid-catalyzed hydrolysis of ethyl formate, which is an ester. This reaction will produce a carboxylic acid (formic acid) and an alcohol (ethanol). The mechanism proceeds through nucleophilic acyl substitution under acidic conditions.
Step 1: Protonation of the ester carbonyl group. The acid catalyst (H⁺) protonates the carbonyl oxygen of ethyl formate, increasing the electrophilicity of the carbonyl carbon. This makes it more susceptible to nucleophilic attack.
Step 2: Nucleophilic attack by water. A water molecule acts as a nucleophile and attacks the carbonyl carbon, forming a tetrahedral intermediate. This intermediate contains a positively charged oxygen atom due to the protonated carbonyl group.
Step 3: Proton transfer. A proton transfer occurs within the intermediate to stabilize the structure. The hydroxyl group (from water) becomes neutral, and one of the ethoxy groups is protonated, making it a good leaving group.
Step 4: Elimination of the leaving group and deprotonation. The ethoxy group (C₂H₅O⁺) leaves, forming ethanol. The remaining intermediate is protonated formic acid, which undergoes deprotonation to yield the final product: formic acid (HCOOH).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Catalyzed Hydrolysis
Acid-catalyzed hydrolysis is a reaction where water is used to break down a compound in the presence of an acid, which increases the reaction rate. In this process, the acid donates protons (H+) to the reactants, facilitating the cleavage of bonds and the formation of products. This mechanism is crucial for understanding how esters, like ethyl formate, are converted into their corresponding acids and alcohols.
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Mechanism of Ester Hydrolysis
The mechanism of ester hydrolysis involves several key steps: protonation of the carbonyl oxygen, nucleophilic attack by water, and subsequent deprotonation. Initially, the acid protonates the carbonyl oxygen, increasing the electrophilicity of the carbon atom. Water then acts as a nucleophile, attacking the carbonyl carbon, leading to the formation of a tetrahedral intermediate, which eventually collapses to yield the acid and alcohol.
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Role of Ethyl Formate
Ethyl formate is an ester formed from formic acid and ethanol. In the context of acid-catalyzed hydrolysis, it serves as the substrate that undergoes reaction with water in the presence of an acid catalyst. Understanding the structure and reactivity of ethyl formate is essential for predicting the products of the hydrolysis reaction, which will yield formic acid and ethanol.
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