MCAT Organic Chemistry Question 167: Answer and Explanation
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Question: 167
2. Which of the following compounds would be most effective in extracting benzoic acid from a diethyl ether solution?
- A. Tetrahydrofuran
- B. Aqueous hydrochloric acid
- C. Aqueous sodium hydroxide
- D. Water
Correct Answer: C
Explanation:
By extracting with sodium hydroxide, benzoic acid will be converted to its sodium salt, sodium benzoate. Sodium benzoate, unlike its conjugate acid, will dissolve in an aqueous solution. The aqueous layer simply has to be acidified to retrieve benzoic acid. Choice (A) is incorrect because diethyl ether and tetrahydrofuran are both nonpolar and are miscible. Hydrochloric acid will not transform benzoic acid into a soluble salt, so choice (B) is incorrect. Finally, choice (D) is incorrect because protonated benzoic acid has low solubility in water.