Which set of reagents are needed to synthesize the given unsymmetrical alkyne `CH_3-C-=C-CH_2-CH_3` ?

Options

A. Acetaldyde , 1 - bromopropane and conc.`H_2SO_4`
B. Ethyne , iodomethane , iodothane and sodamide
C. 1,2 - dichloroethane , 1 - propanol and alcoholic potassium hydroxide
D. Ethene , iodoethane , iodomethane and potassium hydroxide

Answer

To synthesize the unsymmetrical alkyne `CH₃-C≡C-CH₂-CH₃`, we can follow these steps:

### Step 1: Identify the Starting Material
We need to start with a compound that can provide the necessary carbon skeleton and a triple bond. A good starting material is **ethyne (acetylene)**, which has the formula `C₂H₂` or `HC≡CH`.

### Step 2: Deprotonation of Ethyne
Next, we will use **sodium amide (NaNH₂)** to deprotonate ethyne. Sodium amide acts as a strong base and will remove one of the acidic protons from ethyne, resulting in the formation of the acetylide ion:
\[ \text{HC≡CH} + \text{NaNH₂} \rightarrow \text{HC≡C}^- \text{Na}^+ + \text{NH₃} \]

### Step 3: Nucleophilic Attack
The acetylide ion (nucleophile) can now react with a suitable alkyl halide. We will use **methyl iodide (CH₃I)** as the alkyl halide. The nucleophile will attack the carbon atom of the methyl halide, leading to the formation of a new carbon-carbon bond:
\[ \text{HC≡C}^- + \text{CH₃I} \rightarrow \text{CH₃C≡C}^- \text{Na}^+ + \text{I}^- \]

### Step 4: Second Deprotonation
Now we have the compound `CH₃C≡C^-`. We need to add another alkyl group to the terminal carbon. We will use **ethyl iodide (C₂H₅I)** for this step. First, we will deprotonate the terminal alkyne:
\[ \text{CH₃C≡C}^- + \text{NaNH₂} \rightarrow \text{CH₃C≡C}^- \text{Na}^+ + \text{NH₃} \]

### Step 5: Nucleophilic Attack on Ethyl Iodide
The acetylide ion will now attack the ethyl iodide:
\[ \text{CH₃C≡C}^- + \text{C₂H₅I} \rightarrow \text{CH₃C≡C-CH₂-CH₃} + \text{I}^- \]

### Final Product
The final product formed is the unsymmetrical alkyne `CH₃-C≡C-CH₂-CH₃`.

### Summary of Reagents
The reagents needed for this synthesis are:
1. Sodium amide (NaNH₂)
2. Methyl iodide (CH₃I)
3. Ethyl iodide (C₂H₅I)