Principle of differential extraction

Differential extraction separates compounds based on their acid-base behavior.

• Carboxylic acids react with aqueous $NaHCO_3$ and aqueous $NaOH$ to form water-soluble salts.
• Phenols react with aqueous $NaOH$ but do not react with aqueous $NaHCO_3$.
• Alcohols do not react with either $NaOH$ or $NaHCO_3$ and remain in the organic layer.

Relevant behavior of the given compounds

• $C_6H_5COOH$ (benzoic acid): acidic enough to react with $NaHCO_3$ and $NaOH$
• $C_6H_5CH_2COOH$ (phenylacetic acid): acidic enough to react with $NaHCO_3$ and $NaOH$
• $C_6H_5OH$ (phenol): reacts with $NaOH$, but not with $NaHCO_3$
• $C_6H_5CH_2OH$ (benzyl alcohol): does not react with either

Interpret the extraction scheme

The usual scheme implied here is:

• first extract with $NaHCO_3$: only carboxylic acid goes to aqueous layer as salt
• then extract remaining organic layer with $NaOH$: phenol would go to aqueous layer as phenoxide
• neutral compound/alcohol stays in organic layer

Therefore, for a binary mixture to be separated by this scheme, the two compounds must differ in this behavior.

Check each option

Option A: $C_6H_5OH$ and $C_6H_5COOH$

• $C_6H_5COOH$ is removed by $NaHCO_3$.
• $C_6H_5OH$ remains in organic layer and can be separated. Hence this mixture can be separated.

Option B: $C_6H_5COOH$ and $C_6H_5CH_2OH$

• $C_6H_5COOH$ reacts with $NaHCO_3$ and goes to aqueous layer.
• $C_6H_5CH_2OH$ remains in organic layer. Hence this mixture can be separated.

Option C: $C_6H_5CH_2OH$ and $C_6H_5OH$

• $C_6H_5OH$ does not react with $NaHCO_3$, but reacts with $NaOH$.
• $C_6H_5CH_2OH$ remains in organic layer. Hence this mixture can be separated.

Option D: $C_6H_5CH_2OH$ and $C_6H_5CH_2COOH$

• $C_6H_5CH_2COOH$ reacts with $NaHCO_3$ and goes to aqueous layer.
• $C_6H_5CH_2OH$ remains in organic layer. Hence this mixture can be separated.

Derived answer

The binary mixtures that can be separated by differential extraction are: $A,\ B,\ C,\ D$

Comparison with stored answer

Stored correct answer: $B, D$

My derived answer includes $A$ and $C$ as well, because:

• $A$ is separable since carboxylic acid is extracted by $NaHCO_3$, phenol remains.
• $C$ is separable since phenol is extracted by $NaOH$, benzyl alcohol remains.

Therefore, I do not agree with the stored answer.