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

25. Condensation Chemistry

Robinson Annulation

Organic Chemistry

25. Condensation Chemistry

Robinson Annulation

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8:28 minutes

Problem 58

Textbook Question

The base-catalyzed reaction of an aldehyde (having no α hydrogens) with an anhydride is called the Perkin condensation. Propose a mechanism for the following example of the Perkin condensation. (Sodium acetate serves as the base.)

Verified step by step guidance

Step 1: Identify the reactants and the role of the base. The reaction involves benzaldehyde (an aldehyde with no α-hydrogens) and acetic anhydride. Sodium acetate acts as the base to initiate the reaction by deprotonating acetic anhydride.

Step 2: Deprotonation of acetic anhydride. Sodium acetate abstracts a proton from the methyl group of acetic anhydride, forming an enolate ion. The enolate ion is stabilized by resonance, with the negative charge delocalized between the oxygen atoms and the carbon atom.

Step 3: Nucleophilic attack of the enolate ion on benzaldehyde. The enolate ion acts as a nucleophile and attacks the carbonyl carbon of benzaldehyde, forming a tetrahedral intermediate. This intermediate collapses, regenerating the carbonyl group and forming a β-hydroxy intermediate.

Step 4: Elimination of water to form the α,β-unsaturated product. Under the reaction conditions (heat), the β-hydroxy intermediate undergoes dehydration (loss of water) to form cinnamic acid, which is an α,β-unsaturated carboxylic acid.

Step 5: Formation of acetic acid as a byproduct. During the reaction, acetic acid is formed as a byproduct from the hydrolysis of acetic anhydride and the action of the base. The final products are cinnamic acid and acetic acid.

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Key Concepts

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

Perkin Condensation

The Perkin condensation is a reaction between an aldehyde and an anhydride, typically in the presence of a base, to form α,β-unsaturated carboxylic acids. This reaction is significant in organic synthesis as it allows for the formation of carbon-carbon bonds. In this specific case, the aldehyde lacks α-hydrogens, which influences the reaction pathway and product formation.

Mechanism of Base-Catalyzed Reactions

Base-catalyzed reactions involve the use of a base to facilitate the reaction process, often by deprotonating a substrate to generate a more reactive species. In the context of the Perkin condensation, sodium acetate acts as the base, which helps in the formation of the enolate ion from the aldehyde. This enolate then attacks the anhydride, leading to the formation of the desired product.

Role of Anhydrides in Organic Reactions

Anhydrides are reactive compounds that can participate in various organic reactions, including acylation and condensation reactions. In the Perkin condensation, the anhydride provides an acyl group that reacts with the enolate formed from the aldehyde. This reaction is crucial for forming the carbon-carbon bond and ultimately leads to the production of α,β-unsaturated carboxylic acids.

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