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Chapter 12: Problem 14

(a) Show how 2 -butanone could be prepared by a procedure in which all of the carbons originate in acetic acid \(\left(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\right)\). (b) Two species of ants found near the Mediterranean use 2 -methyl-4-heptanone as an alarm pheromone. Suggest a synthesis of this compound from two 4-carbon alcohols.

Short Answer

Expert verified
(a) Prepare 2-butanone by decarboxylating 3-oxobutanoic acid derived from acetic acid. (b) Synthesize 2-methyl-4-heptanone using an aldol reaction with butanol-derived intermediates after selective oxidation.

Step by step solution

01

Understand the Problem for 2-Butanone

We need to synthesize 2-butanone, a four-carbon ketone, using acetic acid as the sole source of carbon atoms. This means each step in the synthesis must rearrange or recombine carbon atoms originating from acetic acid.
02

Assemble 4-Carbon Skeleton for 2-Butanone

Start with two moles of acetic acid (\( \text{CH}_3\text{CO}_2\text{H} \)). Convert acetic acid into acetyl chloride (\( \text{CH}_3\text{COCl} \)) using thionyl chloride (\( \text{SOCl}_2 \)). Then, perform a Claisen condensation using acetyl chloride to form 3-oxobutanoic acid, ensuring a four-carbon skeleton.
03

Complete Synthesis to 2-Butanone

Decarboxylate 3-oxobutanoic acid, removing the carboxyl group as carbon dioxide (\( \text{CO}_2 \)), and consequently forming 2-butanone. This step introduces the ketone functionality as required in the product.
04

Analyze the Requirements for 2-Methyl-4-Heptanone

We need to form 2-methyl-4-heptanone from two 4-carbon alcohols. Identify butanol (\( \text{C}_4\text{H}_9\text{OH} \)) and butane-2,3-diol (\( \text{C}_4\text{H}_{10}\text{O}_2 \)) as the suitable four-carbon alcohols.
05

Form the Longer Carbon Chain via Aldol Condensation

Oxidize butanol to butanal using mild oxidizing agent. Perform an aldol condensation between butanal and butane-2,3-diol's oxidation product to extend the carbon chain, forming the carbon framework needed for 2-methyl-4-heptanone.
06

Complete the Synthesis of 2-Methyl-4-Heptanone

Hydrogenate the aldol product to stabilize the base chain. Finally, perform a selective reduction to remove any excess carbonyl groups, completing the synthesis of 2-methyl-4-heptanone as required for pheromone synthesis.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

2-Butanone synthesis
To synthesize 2-butanone from acetic acid, which is a significant task in organic chemistry, understanding the molecular transformations involved is essential. The procedure begins with using acetic acid
  • Start by converting acetic acid into acetyl chloride through a reaction with thionyl chloride (\( \text{SOCl}_2 \)).
  • This transformation is crucial as acetyl chloride provides a more reactive intermediate.
  • Subsequently, a Claisen condensation with acetyl chloride is performed, resulting in the formation of 3-oxobutanoic acid.
  • This reaction assembles a four-carbon skeleton, essential for 2-butanone synthesis.
The final step in the process is the decarboxylation of 3-oxobutanoic acid, where the carboxyl group is eliminated as carbon dioxide
  • This decarboxylation step is pivotal because it produces the desired ketone functionality.
  • The outcome is the successful formation of 2-butanone, a valuable compound in the chemical industry.
Acetic acid conversion
Acetic acid serves as a versatile starting material in organic synthesis due to its simple structure and functional groups. Its conversion into various reactive derivatives lays the groundwork for further synthesis processes.
  • Conversion to acetyl chloride with thionyl chloride (\( \text{SOCl}_2 \)), allows the introduction of the acid chloride functionality.
  • This conversion is essential as acetyl chloride forms an excellent nucleophile for subsequent reactions.
  • In these transformations, maintaining the integrity of the carbon chain allows a more controlled synthesis pathway.
Thus, acetic acid discussions often spotlight its ability to serve as a carbon repository for broader chemical syntheses, especially in forming complex molecules.
Pheromone synthesis
Synthesizing pheromones, like 2-methyl-4-heptanone used by certain ant species, involves utilizing strategic organic reactions. Here, the synthesis process focuses on building the compound from simpler four-carbon alcohols.
  • Commence with selecting butanol and butane-2,3-diol as starting alcohols, favored for their structural properties.
  • Shortly thereafter, oxidize butanol to butanal using a suitable mild oxidizing agent.
  • This conversion is vital as aldehydes serve as key intermediates in aldol condensations.
By using these alcohols, students can appreciate the practical application of various organic reaction mechanisms to produce complex natural compounds like pheromones.
Aldol condensation
The aldol condensation is a fundamental organic reaction that forms carbon-carbon bonds, crucial in complex molecule synthesis. This reaction becomes especially critical in extending carbon chains.
  • In the context of 2-methyl-4-heptanone synthesis, react butanal with butane-2,3-diol's oxidation products.
  • This results in the creation of a larger carbon framework necessary for synthesizing the target compound.
  • The reaction occurs in basic conditions, enabling the formation of a 尾-hydroxy aldehyde or ketone.
Appreciating aldol condensation's role in synthesis allows students to understand how it contributes to constructing more elaborate organic molecules.
Decarboxylation process
Understanding the decarboxylation process is vital for synthesizing aromatic and aliphatic ketones. This reaction involves removing a carboxyl group as carbon dioxide, a common step in organic synthesis.
  • For the synthesis of 2-butanone, decarboxylation of 3-oxobutanoic acid is crucial.
  • This step eliminates the carboxyl group and results in the formation of the ketone functional group.
  • The process reflects a profound strategy in synthesizing simpler molecules from more complex precursors.
Through this understanding, students can discern how decarboxylation serves as a key step in converting intermediates to desired organic products.

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Most popular questions from this chapter

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