Propane dithioic acid is prepared by the reaction of the following, followed hy hydrolysis :

Options

A. `C_3 H_7 MgBr + CS_2`
B. `C_2H_5 MgBr + CS_2`
C. `C_3 H_7 MgBr + SO_2`
D. `C_2 H_5 Mg Br + SO_2`

Explanation

To prepare propane dithioic acid (C2H5C(=S)SH), we need to follow a specific reaction pathway. Here’s a step-by-step breakdown of the process:

### Step 1: Identify the Reactants
We need to react carbon disulfide (CS2) with ethyl magnesium bromide (C2H5MgBr). Ethyl magnesium bromide is a Grignard reagent, which is a type of organometallic compound.

**Hint:** Grignard reagents are typically formed from alkyl halides and magnesium.

### Step 2: Reaction of Grignard Reagent with Carbon Disulfide
When ethyl magnesium bromide reacts with carbon disulfide, the nucleophilic ethyl group (C2H5-) attacks the electrophilic carbon in carbon disulfide. This forms a thiolate intermediate.

**Hint:** Remember that the nucleophile attacks the electrophile, leading to the formation of a new carbon-sulfur bond.

### Step 3: Formation of Propane Dithioic Acid Intermediate
The reaction can be represented as follows:
\[ C2H5MgBr + CS2 \rightarrow C2H5C(=S)S^-MgBr \]
This intermediate contains the desired structure of propane dithioic acid but still needs to be hydrolyzed.

**Hint:** The product formed at this stage is not the final acid; it is an intermediate that requires further processing.

### Step 4: Hydrolysis of the Intermediate
The next step is hydrolysis, where we add water (H2O) to the reaction mixture. This process converts the thiolate intermediate into propane dithioic acid (C2H5C(=S)SH) and releases magnesium bromide hydroxide (MgBrOH).

**Hint:** Hydrolysis typically involves the addition of water to break down intermediates into their final acid forms.

### Step 5: Final Product
The final product after hydrolysis is propane dithioic acid:
\[ C2H5C(=S)SH \]

**Hint:** Make sure to verify the structure of the final product to ensure it matches the desired compound.

### Conclusion
The correct reactants to prepare propane dithioic acid through the described reaction pathway are carbon disulfide and ethyl magnesium bromide. Therefore, the answer to the question is option B, as it leads to the formation of propane dithioic acid after hydrolysis.