Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids

Problem 29

Chapter 17, Problem 29

How would you reduce the alkene in the presence of a carboxylic acid?

Verified step by step guidance

Identify the functional groups in the molecule: The problem involves an alkene (C=C double bond) and a carboxylic acid (-COOH). The goal is to selectively reduce the alkene without affecting the carboxylic acid.

Choose a reducing agent that is selective for alkenes: Catalytic hydrogenation using H₂ gas with a metal catalyst (e.g., Pd/C, Pt, or Ni) is a common method to reduce alkenes to alkanes. This method does not reduce carboxylic acids under standard conditions.

Set up the reaction conditions: Use a hydrogenation setup with the chosen metal catalyst and H₂ gas. Ensure the reaction is carried out under mild conditions to avoid side reactions or over-reduction.

Monitor the reaction: Use techniques such as thin-layer chromatography (TLC) or gas chromatography (GC) to confirm the disappearance of the alkene and the formation of the alkane product.

Isolate and purify the product: After the reaction is complete, filter off the catalyst, and purify the product using methods like distillation or recrystallization, depending on the physical properties of the compound.

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Key Concepts

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

Alkene Reduction

Alkene reduction refers to the process of converting an alkene, which contains a carbon-carbon double bond, into an alkane by adding hydrogen. This can be achieved through various methods, including catalytic hydrogenation, where hydrogen gas is added in the presence of a catalyst, or through the use of reducing agents. Understanding the mechanisms and conditions for alkene reduction is crucial for effectively answering the question.

Carboxylic Acids

Carboxylic acids are organic compounds characterized by the presence of a carboxyl group (-COOH). They can influence the reactivity of nearby functional groups due to their acidic nature. In the context of alkene reduction, the presence of a carboxylic acid can affect the choice of reducing agent and the reaction conditions, making it essential to consider how these acids interact with alkenes during reduction.

Reducing Agents

Reducing agents are substances that donate electrons in a chemical reaction, thereby reducing another species. Common reducing agents for alkenes include metals like lithium aluminum hydride (LiAlH4) and sodium borohydride (NaBH4). When reducing alkenes in the presence of carboxylic acids, it is important to select a reducing agent that is compatible with the acid to avoid unwanted side reactions or degradation of the acid.

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Reducing Agents

Related Practice

Textbook Question

At the end of a reduction, there was found to be a small amount of unreacted amide along with the amine product dissolved in diethyl ether. How might you remove the amine from the ether?

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Textbook Question

The following carboxylic acids were named incorrectly. Provide the correct name.

(b) 6-bromocyclohexane carboxylic acid

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Textbook Question

The acid-catalyzed hydrolysis of an ester results in the formation of an equal amount of carboxylic acid and alcohol.

(a) Design a flow chart for separating the two products.

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Textbook Question

When a chemist attempted the following reaction sequence, the desired product was not formed.

(a) Why?

(b) Suggest a solution to the problem. [Think about chemistry from the end of Chapter 13.]

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Textbook Question

The absence of what band in the IR spectrum of the product in Figure 18.59 would be consistent with full conversion of the carboxylic acid to an acid chloride?

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Textbook Question

The acid-catalyzed hydrolysis of an ester results in the formation of an equal amount of carboxylic acid and alcohol.

(b) Once separated, how could you distinguish between the carboxylic acid and alcohol using IR spectroscopy?

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