Propanamide ` underset( KOH ) overset( Br _2 ) to A overset( (i) HNO_2 ) underset((ii) Red P,HI) to B ,` here [B ] is :

Options

A. N-ethyl acetamide
B. Propane
C. Ethane
D. Acetone

Answer

To solve the question step by step, let's break down the reactions involved:

### Step 1: Reaction of Propanamide with Bromine and KOH
1. **Identify Propanamide**: The structure of propanamide is \( C_2H_5C(=O)NH_2 \).
2. **Hofmann Bromamide Degradation**: When propanamide reacts with bromine (\( Br_2 \)) in the presence of potassium hydroxide (\( KOH \)), it undergoes Hofmann degradation. This reaction involves the following steps:
- The nitrogen of the amide is deprotonated by the base \( OH^- \), forming a negatively charged nitrogen species.
- This negatively charged nitrogen attacks the bromine molecule, leading to the formation of bromamide.
- The bromamide then loses a carbon atom, resulting in the formation of an amine with one carbon less than the original amide.

3. **Formation of A**: After the Hofmann degradation, we get ethylamine (\( C_2H_5NH_2 \)) as compound A.

### Step 2: Reaction of A (Ethylamine) with HNO2
1. **Reaction with HNO2**: Ethylamine reacts with nitrous acid (\( HNO_2 \)), which can be represented as \( HONO \).
- The nitrogen of the amine (\( NH_2 \)) is protonated by \( HNO_2 \), forming a diazonium ion intermediate (\( C_2H_5N_2^+ \)).
- The diazonium ion then decomposes, releasing nitrogen gas (\( N_2 \)) and forming a carbocation (\( C_2H_5^+ \)).
- The carbocation then reacts with water to form ethanol (\( C_2H_5OH \)).

2. **Formation of Ethanol**: After this reaction, we have ethanol as compound B.

### Step 3: Reaction of Ethanol with Red Phosphorus and HI
1. **Reaction with Red Phosphorus and HI**: Ethanol reacts with red phosphorus and hydroiodic acid (HI).
- Red phosphorus and HI act as reducing agents, converting the alcohol into an alkane.
- The reaction leads to the formation of ethane (\( C_2H_6 \)) and water.

2. **Final Product B**: Thus, the final product B is ethane (\( C_2H_6 \)).

### Final Answer
The structure of compound B is ethane (\( C_2H_6 \)).

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