A sequential reaction may be performed as represented below :
`"RCH"_(2) CO _(2) H underset((i)) (rarr) "RCH"_(2) "COCl" underset((2))overset(NH_(3))(rarr)`
`"RCH"_(2) "CONH"_(2) overset((3))(rarr)`
`"RCO"_(2) H overset((5))(larr)"RCH"_(2) OH overset((4))(larr) "RCH"_(2)NH_(2)`
the appropriate reagent for step (3) is :

Options

A. Bromine alone
B. Bromine and alkali
C. HBr
D. `P_(2) O_(5)`

Explanation

To solve the problem, we need to identify the appropriate reagent for step (3) in the sequential reaction provided. Let's break down the steps:

### Step 1: Analyze the Reaction Sequence
The reaction sequence given is:
1. \( \text{RCH}_2\text{COOH} \) (Carboxylic acid) converts to \( \text{RCH}_2\text{COCl} \) (Acyl chloride).
2. \( \text{RCH}_2\text{COCl} \) reacts with \( \text{NH}_3 \) to form \( \text{RCH}_2\text{CONH}_2 \) (Amide).
3. The next step involves converting \( \text{RCH}_2\text{CONH}_2 \) to \( \text{RCH}_2\text{NH}_2 \) (Primary amine).

### Step 2: Identify the Reagent for Step (3)
In step (3), we need to convert an amide (\( \text{RCH}_2\text{CONH}_2 \)) to a primary amine (\( \text{RCH}_2\text{NH}_2 \)). This transformation typically involves the removal of one carbon atom from the amide.

### Step 3: Recognize the Reaction Type
The reaction that achieves this transformation is known as the **Hofmann degradation** (or Hofmann bromamide degradation). In this reaction, an amide is treated with bromine (Br2) in the presence of a strong base (like NaOH). This results in the loss of one carbon atom, producing a primary amine.

### Step 4: Write the Reaction
The general reaction can be summarized as:
\[ \text{RCH}_2\text{CONH}_2 + \text{Br}_2 + 4 \text{NaOH} \rightarrow \text{RCH}_2\text{NH}_2 + \text{Na}_2\text{CO}_3 + 2 \text{NaBr} + 2 \text{H}_2\text{O} \]

### Conclusion
From the options provided, the appropriate reagent for step (3) is **Bromine and Alkali (NaOH)**.

### Final Answer
The appropriate reagent for step (3) is **Bromine and Alkali (NaOH)**.

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