Which of the following reagents may be used to distinguish between phenol and beznoic acid ?

Options

A. Neutral `FeCl_3`
B. Aqueous NaOH
C. Tollen's reagent
D. Molisch reagent

Answer

To distinguish between phenol and benzoic acid, we can use neutral FeCl3 (ferric chloride). Here’s a step-by-step explanation of how this reagent works in differentiating the two compounds:

### Step 1: Understand the Compounds
- **Phenol (C6H5OH)**: This is an aromatic alcohol.
- **Benzoic Acid (C6H5COOH)**: This is an aromatic carboxylic acid.

### Step 2: Reaction with Neutral FeCl3
- When **phenol** reacts with neutral FeCl3, it forms a complex that gives a **violet coloration**. The reaction can be represented as:
\[ \text{C6H5OH} + \text{FeCl3} \rightarrow \text{Fe(C6H5O)}_3 + 3\text{HCl} \quad (\text{violet complex}) \]

### Step 3: Reaction with Benzoic Acid
- When **benzoic acid** reacts with neutral FeCl3, it forms a **buff-colored precipitate** of ferric benzoate. The reaction can be represented as:
\[ \text{C6H5COOH} + \text{FeCl3} \rightarrow \text{Fe(C6H5COO)}_3 + 3\text{HCl} \quad (\text{buff-colored precipitate}) \]

### Step 4: Observation of Color Change
- The key observation is:
- **Phenol** gives a **violet color** with FeCl3.
- **Benzoic Acid** gives a **buff-colored precipitate** with FeCl3.

### Step 5: Conclusion
- Since the two compounds produce different colors upon reaction with neutral FeCl3, we can effectively distinguish between phenol and benzoic acid using this reagent. Therefore, the correct answer is **neutral FeCl3**.