Which of the given below is best method of preparing alkyl chloride?

Options

A. `ROH +SOCl_(2)`
B. `ROH+PCl_(5)rarr`
C. `ROH +PCl_(3)rarr`
D. `ROH+HCl overset("anhy. ZnCl"_(2))rarr`

Answer

To determine the best method for preparing alkyl chloride from the given options, we will analyze each method based on three criteria: reaction conditions, time efficiency, and ease of separation of side products.

### Step-by-Step Solution:

1. **Identify the Methods**: The methods provided for preparing alkyl chloride are:
- Method 1: ROH + SOCl2 (Thionyl Chloride)
- Method 2: ROH + PCl5
- Method 3: ROH + PCl3
- Method 4: ROH + HCl with anhydrous zinc chloride (Lucas reagent)

2. **Analyze Method 1 (ROH + SOCl2)**:
- **Reaction**: This method produces alkyl chloride (RCl) and side products SO2 (gaseous) and HCl.
- **Conditions**: The reaction conditions are mild, and SO2 being gaseous makes it easy to separate.
- **Time Efficiency**: Generally efficient and quick.
- **Separation**: Easier due to gaseous SO2.

3. **Analyze Method 2 (ROH + PCl5)**:
- **Reaction**: Produces alkyl chloride and side products POCl3 and HCl.
- **Conditions**: Requires harsher conditions than Method 1.
- **Time Efficiency**: Reasonably efficient but not as quick as Method 1.
- **Separation**: POCl3 is a liquid and requires more effort to separate.

4. **Analyze Method 3 (ROH + PCl3)**:
- **Reaction**: Produces alkyl chloride and phosphoric acid as a side product.
- **Conditions**: Similar to Method 2, requiring more effort.
- **Time Efficiency**: Comparable to Method 2.
- **Separation**: Phosphoric acid is a liquid and complicates separation.

5. **Analyze Method 4 (ROH + HCl with anhydrous zinc chloride)**:
- **Reaction**: This is the Lucas reagent method.
- **Conditions**: Requires heating, especially for primary alcohols.
- **Time Efficiency**: Takes more time for primary alcohols, but secondary and tertiary alcohols react faster.
- **Separation**: More complex due to the need for heat and longer reaction times.

6. **Compare the Methods**:
- **Best Reaction Conditions**: Method 1 (SOCl2) has the mildest conditions.
- **Best Time Efficiency**: Method 1 is generally quicker.
- **Easiest Separation**: Method 1 has gaseous SO2, making separation straightforward.

7. **Conclusion**: Based on the analysis, the best method for preparing alkyl chloride is **Method 1: ROH + SOCl2** because it meets all the criteria of mild conditions, efficiency, and ease of separation.

### Final Answer:
The best method for preparing alkyl chloride is **ROH + SOCl2**.