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 21

Chapter 17, Problem 21

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?

Verified step by step guidance

Step 1: Recognize that the amine product and unreacted amide are dissolved in diethyl ether, which is an organic solvent. To separate the amine, we can exploit its basicity and solubility properties.

Step 2: Prepare an aqueous acidic solution, such as dilute hydrochloric acid (HCl). The amine, being a basic compound, will react with the acid to form a water-soluble ammonium salt.

Step 3: Perform a liquid-liquid extraction. Add the aqueous acidic solution to the diethyl ether solution containing the amine and amide. Shake the mixture thoroughly to allow the amine to react with the acid and transfer into the aqueous phase as its ammonium salt.

Step 4: Separate the two layers using a separatory funnel. The aqueous layer will contain the ammonium salt of the amine, while the organic layer will retain the unreacted amide.

Step 5: To recover the amine, neutralize the aqueous layer with a base, such as sodium hydroxide (NaOH), to regenerate the free amine. Extract the amine back into a fresh portion of diethyl ether, if needed.

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Key Concepts

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

Amine Solubility

Amines are organic compounds derived from ammonia by replacement of one or more hydrogen atoms with alkyl or aryl groups. They are generally soluble in polar solvents like water and can also dissolve in organic solvents such as diethyl ether. Understanding the solubility properties of amines is crucial for devising methods to separate them from other compounds in a mixture.

Extraction Techniques

Extraction is a separation technique used to isolate a desired substance from a mixture based on differences in solubility. In this context, liquid-liquid extraction can be employed to separate the amine from the ether solution by using a polar solvent that selectively dissolves the amine, allowing it to be removed from the non-polar ether phase.

Recrystallization

Recrystallization is a purification technique that involves dissolving a solid in a hot solvent and then allowing it to crystallize as it cools. This method can be useful for isolating pure amines from a mixture, as the desired amine can be selectively crystallized out of solution, leaving behind impurities and unreacted amides.

Related Practice

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

Predict the product of the following reactions.

(a)

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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

How would you reduce the alkene in the presence of a 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.

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

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