Hofmann's method to separate amines in a mixture uses the
reagent:-

Options

A. Benzenesulphonyl chloride
B. Diethyl oxalate
C. Benzeneisocyanide
D. p-toluenesulphonic acid

Answer

To solve the question regarding Hofmann's method for separating amines in a mixture, we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Hofmann's Method**:
Hofmann's method is a chemical process used to separate different types of amines, specifically primary, secondary, and tertiary amines.

2. **Identifying the Reagent**:
The reagent used in Hofmann's method is crucial for the separation process. The specific reagent that is used is diethyl oxalate.

3. **Chemical Structure of Diethyl Oxalate**:
Diethyl oxalate has the following chemical structure:
\[ \text{OC}_2\text{H}_5 - \text{C}(=O) - \text{C}(=O) - \text{OC}_2\text{H}_5 \]
This indicates that it contains two ethyl groups attached to an oxalate functional group.

4. **Reactions with Amines**:
- **Primary Amines**: When diethyl oxalate reacts with primary amines, it forms a solid product known as oxamide.
- **Secondary Amines**: When it reacts with secondary amines, it produces a liquid product called oxamic ester.
- **Tertiary Amines**: Tertiary amines do not react with diethyl oxalate, which allows for their separation from primary and secondary amines.

5. **Conclusion**:
Based on the reactions and the properties of the reagent, we conclude that the reagent used in Hofmann's method to separate amines in a mixture is diethyl oxalate.

### Final Answer:
The reagent used in Hofmann's method to separate amines in a mixture is **diethyl oxalate**.