Question

In the above conversion of compound $( X )$ to product $( Y )$, the sequence of reagents to be used will be:

• A. (i) $Fe , H ^{+}$ (ii)$ Br _2( aq ) $ (iii) $ HNO _2$ (iv) $CuBr$
• B. (i) $Fe , H ^{+}$ (ii) $Br _2( aq )$ (iii) $HNO _2$ (iv) $H _3 PO _2$
• C. (i) $Br _2, Fe$ (ii) $Fe , H ^{+}$ (iii) $LiAIH _4$
• D. (i) $Br _2( aq )$ (ii) $LiAIH _4$ (iii) $H _3 O ^{+}$

Answer 1

The Correct Option is B

This question involves the conversion of compound \((X)\), which is a nitro compound, to the desired product \((Y)\). The sequence of reagents must align with the chemical reactions needed to transform the initial nitro compound into the brominated aromatic compound.

1. Step 1: Reduction of the Nitro Group
   The first step involves reducing the nitro group \((-NO_2)\) of the compound \((X)\) to an amino group \((-NH_2)\). This can be achieved using iron and an acid, like \(Fe, H^+\).
2. Step 2: Diazotization
   Convert the amino group \((-NH_2)\) to a diazonium salt using \(HNO_2\) (nitrous acid). This reaction is crucial for enabling subsequent transformations.
3. Step 3: Sandmeyer Reaction (Bromo Substitution)
   Replace the diazonium group with a bromine atom using \(CuBr\). This is part of the Sandmeyer reaction series, which allows the substitution of diazonium salts.
4. Alternative for Bromination
   Another method to brominate involves the use of \(Br_2(aq)\). Since the aim is to form a dibromo product, direct bromination can follow once the amino group is handled appropriately.
5. Step 4: Hypophosphorous Acid (Destruction of Excess Aryl Diazonium)
   Any excess diazonium salt can be destroyed using \(H_3PO_2\), ensuring the reaction’s stability and purity of the final product.

Upon analysis, the correct sequence of reagents that can convert compound \((X)\) to \((Y)\) is:

• \(Fe , H^+\) (Reduction)
• \(Br_2(aq)\) (Bromination)
• \(HNO_2\) (Diazotization)
• \(H_3PO_2\) (Stabilization)

The correct answer is: \((i) Fe , H^+; (ii) Br_2(aq); (iii) HNO_2; (iv) H_3PO_2\)