Textbook Question
Explain why the following carboxylic acids cannot be prepared by a malonic ester synthesis:
c.
24. Enolate Chemistry: Reactions at the Alpha-Carbon
Malonic Ester Synthesis
5:37 minutesProblem 72
Textbook Question
Show how you would use the malonic ester synthesis to make the following compounds.
Verified step by step guidance1
Step 1: Understand the malonic ester synthesis. It is a method used to synthesize carboxylic acids by alkylating diethyl malonate (a malonic ester) and then hydrolyzing and decarboxylating the product. The key steps involve enolate formation, alkylation, hydrolysis, and decarboxylation.
Step 2: For compound (a), cyclohexylacetic acid: Start with diethyl malonate. Use a base like sodium ethoxide to form the enolate ion. Then, alkylate the enolate with cyclohexylmethyl bromide (or a similar alkyl halide) to introduce the cyclohexyl group.
Step 3: For compound (b), phenylbutyric acid: Begin with diethyl malonate. Form the enolate using a base, and then alkylate it with phenylethyl bromide (or a similar alkyl halide) to introduce the phenylethyl group. This will extend the chain to include the phenyl group.
Step 4: For compound (c), cyclopentylacetic acid: Start with diethyl malonate. Form the enolate using a base, and then alkylate it with cyclopentylmethyl bromide (or a similar alkyl halide) to introduce the cyclopentyl group.
Step 5: For all compounds (a), (b), and (c): After alkylation, hydrolyze the ester groups using aqueous acid (e.g., HCl) to form the dicarboxylic acid. Then, decarboxylate the product by heating to remove one carboxyl group, yielding the desired carboxylic acid.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Malonic Ester Synthesis
Malonic ester synthesis is a method for synthesizing carboxylic acids by using malonic ester as a key intermediate. This reaction involves the alkylation of a malonic ester followed by hydrolysis and decarboxylation, allowing for the introduction of alkyl groups and the formation of a carboxylic acid. It is particularly useful for creating compounds with a specific carbon chain length and functional groups.
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Decarboxylation
Decarboxylation is the process of removing a carboxyl group (-COOH) from a molecule, resulting in the release of carbon dioxide (CO2). In the context of malonic ester synthesis, decarboxylation occurs after hydrolysis, leading to the formation of a carbonyl compound. This step is crucial for obtaining the final product with the desired structure and functional groups.
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Functional Group Transformation
Functional group transformation refers to the process of converting one functional group into another within a molecule. In malonic ester synthesis, the introduction of various functional groups, such as hydroxyl (-OH) or carbonyl (C=O) groups, can be achieved through strategic reactions. Understanding how to manipulate functional groups is essential for designing synthetic pathways to achieve specific target compounds.
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