Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

22. Carboxylic Acid Derivatives: NAS

Acid-Catalyzed Ester Hydrolysis

Organic Chemistry

22. Carboxylic Acid Derivatives: NAS

Acid-Catalyzed Ester Hydrolysis

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3:05 minutes

Problem 49d

Textbook Question

Propose mechanisms for the following reactions.
(d)

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Identify the starting material as a bicyclic anhydride and the product as a lactone with an ester group. The reaction involves a ring-opening and formation of a new ring.

Recognize that the ethoxide ion (EtO-) acts as a nucleophile, which will attack the carbonyl carbon of the anhydride, leading to the opening of the anhydride ring.

After the nucleophilic attack, the intermediate formed will have a carboxylate group and an alkoxide group. The alkoxide can then undergo intramolecular nucleophilic attack on the other carbonyl group, leading to the formation of a new ring.

The intramolecular attack results in the formation of a five-membered lactone ring, with the carboxylate group being converted into an ester group through the reaction with ethanol (EtOH).

Finally, the stereochemistry of the product is determined by the configuration of the starting material and the mechanism of the reaction, resulting in the observed stereochemistry of the hydroxyl and ester groups in the product.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ester Hydrolysis

Ester hydrolysis is a chemical reaction where an ester is converted into an alcohol and a carboxylic acid or its salt. This process can occur under acidic or basic conditions. In basic hydrolysis, also known as saponification, the ester reacts with a base, such as sodium hydroxide, to form an alcohol and a carboxylate salt.

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks the carbonyl carbon of an acyl compound, leading to the substitution of the leaving group. This mechanism is crucial in the transformation of esters into other functional groups, such as alcohols and carboxylic acids, especially under basic conditions.

Base-Catalyzed Reaction

In a base-catalyzed reaction, a base facilitates the reaction by deprotonating a reactant, increasing its nucleophilicity. In the context of ester hydrolysis, the base (EtO-) deprotonates the alcohol, enhancing its ability to attack the ester carbonyl carbon, leading to the formation of the hydrolysis products. This mechanism is essential for understanding the role of bases in organic transformations.

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Textbook Question

Suppose we have some optically pure (R)-2-butyl acetate that has been "labeled" with the heavy ¹⁸O isotope at one oxygen atom as shown.

(b) Repeat part (a) for the acid-catalyzed hydrolysis of this compound.

Textbook Question

Propose a mechanism for the acid-catalyzed hydrolysis of phenylalanine ethyl ester.

Textbook Question

The Reformatsky reaction is an addition reaction in which an organozinc reagent is used instead of a Grignard reagent to add to the carbonyl group of an aldehyde or a ketone. Because the organozinc reagent is less reactive than a Grignard reagent, a nucleophilic addition to the ester group does not occur.

The organozinc reagent is prepared by treating an α-bromo ester with zinc.

Describe how each of the following compounds can be prepared, using a Reformatsky reaction:

Textbook Question

Propose mechanisms for the following reactions.

(c)

Textbook Question

The mechanism for acidic hydrolysis of a nitrile resembles the basic hydrolysis, except that the nitrile is first protonated, activating it toward attack by a weak nucleophile (water). Under acidic conditions, the proton transfer (tautomerism) involves protonation on nitrogen followed by deprotonation on oxygen. Propose a mechanism for the acid-catalyzed hydrolysis of benzonitrile to benzamide.

Textbook Question

Compare each of the mechanisms listed here with the mechanism for each of the two parts of the acid-catalyzed hydrolysis of an ester, indicating a. similarities. b. differences.

4. acid-catalyzed hydrolysis of an amide

Textbook Question

What products would you expect to obtain from the following reactions?

c. urea + water

d. β-ethylglutaric acid + acetyl chloride + Δ

Textbook Question

Which ester hydrolyzes more rapidly? a. methyl acetate or phenyl acetate?

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