Ch. 20 - Carboxylic Acids

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch. 20 - Carboxylic Acids

Problem 12b

Chapter 20, Problem 12b

Propose a mechanism for the acid-catalyzed reaction of acetic acid with ethanol to give ethyl acetate.

Verified step by step guidance

Step 1: Protonation of the carbonyl oxygen in acetic acid: The reaction begins with the acid catalyst (e.g., H⁺) protonating the carbonyl oxygen of acetic acid. This increases the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack.

Step 2: Nucleophilic attack by ethanol: The lone pair of electrons on the oxygen atom of ethanol attacks the electrophilic carbonyl carbon of the protonated acetic acid, forming a tetrahedral intermediate.

Step 3: Proton transfer: A proton transfer occurs within the intermediate to stabilize the structure. This step involves the transfer of a proton from the positively charged oxygen (from ethanol) to one of the hydroxyl groups in the intermediate.

Step 4: Elimination of water: The intermediate undergoes a dehydration step, where a water molecule is eliminated. This results in the formation of a protonated ethyl acetate intermediate.

Step 5: Deprotonation to regenerate the catalyst: The protonated ethyl acetate loses a proton (H⁺), regenerating the acid catalyst and yielding the final product, ethyl acetate.

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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 this context, the acid donates protons (H+) to the reactants, facilitating the formation of intermediates that lead to the desired product. Understanding the role of the acid is crucial for proposing a mechanism, as it influences the reaction pathway and the stability of intermediates.

Esterification

Esterification is a chemical reaction that forms an ester from an alcohol and a carboxylic acid, typically in the presence of an acid catalyst. In this case, acetic acid reacts with ethanol to produce ethyl acetate. Recognizing the general structure and properties of esters helps in understanding the transformation and the significance of the functional groups involved.

Reaction Mechanism

A reaction mechanism outlines the step-by-step sequence of elementary reactions that occur during a chemical transformation. For the esterification of acetic acid and ethanol, the mechanism includes protonation of the carbonyl oxygen, nucleophilic attack by ethanol, and subsequent elimination of water. Grasping the mechanism is essential for predicting the behavior of reactants and the formation of products.

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Related Practice

Textbook Question

The Principle of Microscopic Reversibility states that a forward reaction and a reverse reaction taking place under the same conditions (as in an equilibrium) must follow the same reaction pathway in microscopic detail. The reverse of the Fischer esterification is the acid-catalyzed hydrolysis of an ester. Propose a mechanism for the acid-catalyzed hydrolysis of ethyl benzoate, PhCOOCH₂CH₃.

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Textbook Question

Show how Fischer esterification might be used to form the following esters. In each case, suggest a method for driving the reaction to completion.

(a) methyl salicylate

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Textbook Question

Show how you would synthesize the following carboxylic acids, using the indicated starting materials.

(e) p-xylene → terephthalic acid

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Textbook Question

Show how you would synthesize the following carboxylic acids, using the indicated starting materials.

(f) allyl iodide → but-3-enoic acid

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Textbook Question

A carboxylic acid has two oxygen atoms, each with two nonbonding pairs of electrons.

(a) Draw the resonance forms of a carboxylic acid that is protonated on the hydroxy oxygen atom.

(b) Compare the resonance forms with those given previously for an acid protonated on the carbonyl oxygen atom.

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Textbook Question

Show how you would synthesize the following carboxylic acids, using the indicated starting materials.

(d) butan-2-ol → 2-methylbutanoic acid