Ch. 4 - Acids and Bases: Electron Flow

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

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Mullins 1st Edition

Ch. 4 - Acids and Bases: Electron Flow

Problem 67

Chapter 3, Problem 67

Suggest a scheme by which N-methylmorpholine, salicylic acid, and naphthalene can be separated.

Verified step by step guidance

Step 1: Analyze the chemical properties of the three compounds. N-methylmorpholine is a basic amine due to the nitrogen atom, salicylic acid is an acidic compound due to the carboxylic acid group, and naphthalene is a neutral aromatic hydrocarbon.

Step 2: Begin separation by exploiting the acid-base properties. Add a dilute acid (e.g., HCl) to the mixture. This will protonate N-methylmorpholine, converting it into a water-soluble salt, while salicylic acid and naphthalene remain unaffected.

Step 3: Extract the aqueous layer containing the protonated N-methylmorpholine. The organic layer will contain salicylic acid and naphthalene. Neutralize the aqueous layer with a base (e.g., NaOH) to regenerate N-methylmorpholine, which can then be extracted back into an organic solvent.

Step 4: Separate salicylic acid and naphthalene by exploiting their solubility differences. Add a dilute base (e.g., NaOH) to the organic layer. This will deprotonate salicylic acid, converting it into a water-soluble salt, while naphthalene remains in the organic layer.

Step 5: Extract the aqueous layer containing the salicylic acid salt. Neutralize it with a dilute acid (e.g., HCl) to regenerate salicylic acid, which can then be extracted back into an organic solvent. Naphthalene remains in the organic layer and can be isolated by evaporation of the solvent.

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Key Concepts

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

Solubility Principles

Understanding solubility is crucial for separating compounds based on their physical properties. N-methylmorpholine is a polar amine, salicylic acid is a weak acid, and naphthalene is a nonpolar hydrocarbon. By exploiting differences in solubility in various solvents, one can selectively dissolve and separate these compounds.

Acid-Base Chemistry

Acid-base chemistry plays a significant role in the separation of salicylic acid from the other compounds. Salicylic acid can be deprotonated to form its anionic form in a basic solution, making it soluble in water, while N-methylmorpholine and naphthalene remain less soluble. This property can be utilized to separate salicylic acid from the mixture.

Extraction Techniques

Extraction techniques, such as liquid-liquid extraction, are essential for separating compounds based on their solubility in different solvents. By choosing appropriate solvents, one can selectively extract N-methylmorpholine, salicylic acid, and naphthalene from the mixture. This method allows for the isolation of each compound based on their unique chemical properties.

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For each of the following molecules, predict the product that would form upon reaction of a single equivalent of a strong base.

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For each of the following molecules, predict the product that would form upon reaction of a single equivalent of a strong base.

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Using pK_a values for the conjugate acids of the bases on each side of the reaction arrow, identify which side of the equilibrium would be favored in the following hypothetical reactions.

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