Question

You have a mixture of 3-fluorophenol and ethyl-4-aminobenzoate that you wish to separate by extraction. The mixture is dissolved in methylene chloride. Why can you not use NaHCO3 to separate one component from the other? (explain why NaHCO3 cannot either component into the aqueous layer).

Answer 1

Answer:

Both 3-fluorophenol and ethyl-4-aminobenzoate remain present in organic layer during extraction.

Explanation:

• Aqueous solution of $NaHCO_{3}$ contains majorly $H_{2}CO_{3}$ in solution.

• Ethyl-4-amino benzoate does not suffer side reaction e.g. ester hydrolysis with $NaHCO_{3}$ to generate more polar ethyl-4-amino benzoate. Hence ethyl-4-amino benzoate remain entirely present in organic layer of methylene chloride.

• 3-fluorophenol has $pK_{a}$ value around 8.4 and $H_{2}CO_{3}$ has $pK_{a}$ value around 6. Therefore 3-fluorophenol does not act as an acid towards aqueous sodium bicarbonate solution.
• Therefore 3-fluorophenol also remains entirely in organic layer of methylene chloride.
• Hence extraction of the given mixture will be unsuccessful with aqueous solution of sodium bicarbonate.