Textbook Question
Predict the products of the following reactions.
(h)
24. Enolate Chemistry: Reactions at the Alpha-Carbon
Acetoacetic Ester Synthesis
Problem 41a
Textbook Question
What alkyl bromide should be used in the acetoacetic ester synthesis of each of the following methyl ketones? a. 2-pentanone
Verified step by step guidance1
Step 1: Understand the acetoacetic ester synthesis. This reaction involves the alkylation of ethyl acetoacetate (a β-keto ester) followed by hydrolysis and decarboxylation to produce a methyl ketone. The key step is identifying the alkyl bromide that will introduce the desired alkyl group to the β-keto ester.
Step 2: Analyze the target molecule, 2-pentanone. The structure of 2-pentanone is CH3-CO-CH2-CH2-CH3. This indicates that the methyl ketone has a CH3 group on one side of the carbonyl and a CH2CH2CH3 group on the other side.
Step 3: Recognize that the CH3 group comes from the ethyl acetoacetate itself. The remaining CH2CH2CH3 group must be introduced via alkylation using an appropriate alkyl bromide.
Step 4: Determine the alkyl bromide needed. To add the CH2CH2CH3 group, the alkyl bromide should be 1-bromopropane (CH3CH2CH2Br). This will react with the enolate of ethyl acetoacetate during the alkylation step.
Step 5: Summarize the process. The synthesis involves deprotonating ethyl acetoacetate to form the enolate, reacting it with 1-bromopropane to introduce the CH2CH2CH3 group, and then performing hydrolysis and decarboxylation to yield 2-pentanone.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acetoacetic Ester Synthesis
Acetoacetic ester synthesis is a method for forming ketones through the reaction of an acetoacetic ester with an alkyl halide. This reaction involves the nucleophilic substitution of the ester enolate with the alkyl halide, leading to the formation of a new carbon-carbon bond. Understanding this process is crucial for determining the appropriate alkyl bromide to use for synthesizing specific ketones.
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Enolate Formation
Enolate formation is a key step in acetoacetic ester synthesis, where a base abstracts a proton from the alpha carbon of the acetoacetic ester, generating a resonance-stabilized enolate ion. This enolate can act as a nucleophile, attacking the electrophilic carbon of the alkyl halide. Recognizing how to generate and utilize enolates is essential for predicting the outcome of the synthesis.
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Alkyl Halides
Alkyl halides, such as alkyl bromides, are organic compounds containing a carbon atom bonded to a halogen atom. The choice of alkyl halide in acetoacetic ester synthesis affects the structure of the resulting ketone. Understanding the reactivity and structure of different alkyl halides is important for selecting the correct one to achieve the desired methyl ketone from the synthesis.
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