Catalyst used in dimerisation of acetylene to prepare chloroprene is

Options

A. `HgSO_4 + H_2SO_4`
B. `Cu_2Cl_2`
C. `Cu_2Cl_2 + NH_4Cl`
D. `Cu_2Cl_2 + NH_4OH`

Explanation

To solve the question regarding the catalyst used in the dimerization of acetylene to prepare chloroprene, we can follow these steps:

### Step 1: Understand the Dimerization Process
The dimerization of acetylene involves the combination of two acetylene (C2H2) molecules to form a larger compound. This process is crucial for the synthesis of chloroprene.

**Hint:** Look for reactions where two molecules combine to form a new compound.

### Step 2: Identify the Catalyst Options
We have four options for the catalyst:
1. HgSO4 + H2SO4
2. Cu2Cl2
3. Cu2Cl2 + NH4Cl
4. Cu2Cl2 + NH4OH

**Hint:** Focus on the catalysts that are commonly used in the dimerization of alkynes.

### Step 3: Analyze the Catalysts
- **HgSO4 + H2SO4**: This combination is typically used in hydration reactions, not specifically for dimerization of acetylene.
- **Cu2Cl2**: This is a copper(I) chloride, which is known to participate in various reactions, but we need to check if it can effectively dimerize acetylene.
- **Cu2Cl2 + NH4Cl**: This combination is known to facilitate the dimerization of acetylene to form vinylacetylene.
- **Cu2Cl2 + NH4OH**: While this may also participate in reactions, it is not the most common catalyst for this specific dimerization.

**Hint:** Consider which catalysts are specifically mentioned in literature for the dimerization of acetylene.

### Step 4: Determine the Product Formation
When acetylene is dimerized using Cu2Cl2 and NH4Cl, it forms vinylacetylene (C4H4). This compound can then react with HCl to produce chloroprene (C4H5Cl).

**Hint:** Think about the end products and how they relate to the catalysts used.

### Step 5: Conclude the Correct Catalyst
Based on the analysis, the catalyst that is used for the dimerization of acetylene to prepare chloroprene is **Cu2Cl2 + NH4Cl**.

**Final Answer:** The correct answer is option number 3: **Cu2Cl2 + NH4Cl**.

### Summary of Steps:
1. Understand the dimerization process.
2. Identify the catalyst options.
3. Analyze the catalysts based on their common uses.
4. Determine the product formation from the dimerization.
5. Conclude the correct catalyst based on the analysis.