Which of the following method gives better yield of p-nitrophenol?

Options

A. Phenol `underset(20^@ C)overset(dil. HNO_3)to ` p-Nitrophenol
B. Phenol `underset((ii) NHO_3)overset((i) NaNO_2 + H_2 SO_4, 7-8^@ C)to ` p-Nitrophenol
C. Phenol `underset((ii) "Conc." HNO_3)overset((i) NaOH)to`
D. None of the three

Answer

To determine which method gives a better yield of p-nitrophenol, we can analyze the two methods mentioned in the video transcript.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- p-Nitrophenol can be synthesized through the nitration of phenol. The two methods typically involve treating phenol with different reagents.

2. **Method 1**: Direct Nitration of Phenol
- In this method, phenol is treated directly with nitric acid (HNO3).
- The reaction can lead to both ortho and para substitution, resulting in a mixture of products.
- Due to the presence of the hydroxyl (OH) group, the reaction may also lead to oxidation of the phenol, which can decrease the yield of p-nitrophenol.

3. **Method 2**: Indirect Nitration via p-Nitroso Phenol
- In this method, phenol is first treated with sodium nitrite (NaNO2) and sulfuric acid (H2SO4) at low temperatures (7-8°C) to form p-nitroso phenol.
- The p-nitroso phenol is then nitrated using HNO3 to introduce the nitro group (NO2) at the para position.
- This method minimizes the oxidation of the hydroxyl group and favors the formation of p-nitrophenol, leading to a higher yield.

4. **Comparison of Yields**:
- Method 1 (direct nitration) results in a mixture of products and potential loss of yield due to oxidation.
- Method 2 (indirect nitration) specifically targets the formation of p-nitrophenol with minimized side reactions, providing a better yield.

5. **Conclusion**:
- The better yield of p-nitrophenol is obtained from Method 2, which involves the formation of p-nitroso phenol followed by nitration.

### Final Answer:
The method that gives a better yield of p-nitrophenol is **Method 2** (treating phenol with NaNO2 and H2SO4 to form p-nitroso phenol, followed by nitration with HNO3).