One mole of 1,2-dibromopropane on treatment with X moles off `NaNH_(2)` followed by treatment with ethyl bromide gave a 2-pentyne. The value of X is

Options

A. one
B. two
C. three
D. four

Explanation

To solve the problem, we need to determine the number of moles of sodium amide (NaNH₂) required to convert 1 mole of 1,2-dibromopropane into 2-pentyne. Let's break down the steps:

### Step 1: Understand the structure of 1,2-dibromopropane
1,2-dibromopropane has the following structure:
- CH₃-CHBr-CH₂Br

### Step 2: Reaction with NaNH₂
When 1,2-dibromopropane reacts with sodium amide (NaNH₂), it undergoes elimination reactions. Each mole of NaNH₂ can remove a bromine atom and form a double bond.

1. The first mole of NaNH₂ will remove one bromine atom (from the carbon with the bromine) and form a double bond between the first and second carbon atoms, resulting in propene (CH₃-CH=CH₂).
2. The second mole of NaNH₂ will then remove the second bromine atom from the second carbon, forming a triple bond between the first and second carbon atoms, resulting in propyne (CH₃-C≡CH).

### Step 3: Reaction with ethyl bromide
Now, we need to treat the propyne with ethyl bromide (CH₃-CH₂Br) in the presence of NaNH₂.

1. The propyne (CH₃-C≡CH) will react with NaNH₂, which will remove a hydrogen atom from the terminal carbon, creating a carbanion (CH₃-C≡C⁻).
2. This carbanion can then attack the ethyl bromide via an SN2 mechanism, resulting in the formation of 2-pentyne (CH₃-CH₂-C≡C-CH₂-CH₃).

### Step 4: Calculate the total moles of NaNH₂ used
- **First step:** 2 moles of NaNH₂ are used to convert 1,2-dibromopropane to propyne.
- **Second step:** 1 mole of NaNH₂ is used to generate the carbanion from propyne.

Thus, the total moles of NaNH₂ required is:
\[ 2 \text{ (for the first step)} + 1 \text{ (for the second step)} = 3 \text{ moles} \]

### Conclusion
The value of X, which represents the number of moles of NaNH₂ required, is **3**.

---