The `-OH` group of an alcohol or of the `-COOH` group of a carboxylic acid can be replaced by `-Cl` using

Options

A. Hypochlorous acid
B. Chlorine
C. Hydrochloric acid
D. Phosphorous pentachloride

Answer

To solve the question regarding the replacement of the `-OH` group of an alcohol or the `-COOH` group of a carboxylic acid by `-Cl`, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Functional Groups**:
- The `-OH` group is characteristic of alcohols.
- The `-COOH` group is characteristic of carboxylic acids.

2. **Determine the Reagent for Chlorination**:
- We need a reagent that can effectively replace these functional groups with chlorine. The video mentions PCl5 (phosphorus pentachloride) as a suitable chlorinating agent.

3. **Reaction with Alcohol**:
- When an alcohol (e.g., ethyl alcohol) reacts with PCl5, the reaction can be represented as:
\[ \text{C}_2\text{H}_5\text{OH} + \text{PCl}_5 \rightarrow \text{C}_2\text{H}_5\text{Cl} + \text{POCl}_3 + \text{HCl} \]
- Here, the `-OH` group is replaced by `-Cl`, forming ethyl chloride.

4. **Reaction with Carboxylic Acid**:
- Similarly, when a carboxylic acid (e.g., acetic acid) reacts with PCl5, the reaction can be represented as:
\[ \text{CH}_3\text{COOH} + \text{PCl}_5 \rightarrow \text{CH}_3\text{COCl} + \text{POCl}_3 + \text{HCl} \]
- In this case, the `-COOH` group is replaced by `-Cl`, forming acetyl chloride.

5. **Conclusion**:
- Therefore, the `-OH` group of an alcohol or the `-COOH` group of a carboxylic acid can be replaced by `-Cl` using PCl5.

### Final Answer:
The `-OH` group of an alcohol or the `-COOH` group of a carboxylic acid can be replaced by `-Cl` using **PCl5**.