Q.Match the compounds given in Column I with the items given in Column II.
Column I:

Concept: Oxidation Reactions (though this question is about identification of reagents and properties — not oxidation directly; the key is matching functional-group behaviour).

Reasoning:

1. Benzene sulphonyl chloride is the classic Hinsberg reagent used to distinguish primary, secondary, and tertiary amines.
2. Sulphanilic acid exists as a zwitter ion because the amino group is basic and the sulphonic acid group is acidic — internal salt formation. …

Let’s break down each compound and its matching item by understanding the chemistry behind it.

1. Benzene sulphonyl chloride (i) → Hinsberg reagent (b)

Benzene sulphonyl chloride, $\ce{C6H5SO2Cl}$, is famously known as the Hinsberg reagent. It is used to distinguish between primary, secondary, and tertiary amines. The reaction works because:

• Primary amines react to form a sulphonamide that is soluble in alkali (due to an acidic N–H bond).
• Secondary amines form a sulphonamide that is insoluble in alkali (no N–H bond).
• Tertiary amines do not react at all.

2. Sulphanilic acid (ii) → Zwitter ion (a)

Sulphanilic acid has the structure $\ce{H2N-C6H4-SO3H}$. Notice it contains both a basic amino group ($\ce{-NH2}$) and an acidic sulphonic acid group ($\ce{-SO3H}$). In the solid state or in neutral solution, the acidic group donates a proton to the basic group, forming an internal salt called a zwitter ion:

This is why sulphanilic acid is insoluble in organic solvents but soluble in water — the ionic character dominates.

3. Alkyl diazonium salts (iii) → Conversion to alcohols (d)

Alkyl diazonium salts, $\ce{R-N2^{+}X^{-}}$, are extremely unstable. Even at low temperatures (0–5°C), they decompose readily. When treated with water, they undergo hydrolysis to give alcohols:

$\ce{R-N2^{+} + H2O -> R-OH + N2 + H+}$ …

Concept: Reactions of Amines and Diazonium Salts

This question tests your understanding of functional group transformations and characteristic reactions of nitrogen-containing organic compounds.

Method: Reagent–Function Matching

Step 1: Identify the key property or use of each compound in Column I.

• (i) Benzene sulphonyl chloride — This is the Hinsberg reagent. It reacts with primary and secondary amines to form sulphonamides, distinguishing them from tertiary amines.
• (ii) Sulphanilic acid — Contains both an amino group ($-NH_2$) and a sulphonic acid group ($-SO_3H$). In solution, it exists as a zwitter ion (internal salt).
• (iii) Alkyl diazonium salts — Unstable; decompose readily to give alcohols (via $S_N1$ or $S_N2$ with water).
• (iv) Aryl diazonium salts — Stable at low temperatures; used in coupling reactions to form azo dyes.

Step 2: Match each with the correct item in Column II.

Here are the common mistakes students make when matching these compounds, along with the correct reasoning to avoid them.

Mistake 1: Confusing Alkyl and Aryl Diazonium Salts

• The Mistake: Students often match Alkyl diazonium salts (iii) with (d) Conversion to alcohols and Aryl diazonium salts (iv) with (c) Dyes. While the second match is correct, the first is dangerously wrong.
• Why it happens: Students remember that diazonium salts react with water to give alcohols. They forget that alkyl diazonium salts are extremely unstable and cannot be isolated or used in practical organic synthesis.
• How to Avoid:
  • Remember the stability rule: Aryl diazonium salts are stable at 0-5°C. Alkyl diazonium salts decompose instantly into carbocations and nitrogen gas ($N_2$).
  • Focus on the reaction: The conversion to alcohols (via hydrolysis) is a classic reaction of aryl diazonium salts (e.g., $C_6H_5N_2^+Cl^- + H_2O \rightarrow C_6H_5OH + N_2 + HCl$).
  • Correct Match: (iv) Aryl diazonium salts → (d) Conversion to alcohols.

Mistake 2: Forgetting the Zwitterion Structure of Sulphanilic Acid

• The Mistake: Students match Sulphanilic acid (ii) with (b) Hinsberg reagent or (c) Dyes, missing the zwitterion property.
• Why it happens: Students see "acid" in the name and think it behaves like a normal acid. They don't visualize the internal salt formation.
• How to Avoid:
  • Draw the structure: Sulphanilic acid has both an acidic $-SO_3H$ group and a basic $-NH_2$ group. In the solid state and in solution, a proton transfers from the acid to the amine.
  • Learn the definition: A zwitterion is a molecule with equal positive and negative charges but a net zero charge. The structure is $^+H_3N-C_6H_4-SO_3^-$.
  • Correct Match: (ii) Sulphanilic acid → (a) Zwitter ion.

Mistake 3: Misidentifying the Hinsberg Reagent

• The Mistake: Students match Benzene sulphonyl chloride (i) with (c) Dyes or (d) Conversion to alcohols, failing to recognize its specific test-tube function.
• Why it happens: The name "benzene sulphonyl chloride" sounds like a complex compound, and students don't connect it to the familiar "Hinsberg reagent" from the amines chapter.
• How to Avoid:
  • Memorize the common name: The Hinsberg reagent is benzenesulphonyl chloride ($C_6H_5SO_2Cl$). It is used to distinguish between primary, secondary, and tertiary amines.
  • Link the function: It reacts with amines to form sulphonamides, which are either soluble or insoluble in alkali, allowing identification.
  • Correct Match: (i) Benzene sulphonyl chloride → (b) Hinsberg reagent.

Mistake 4: Overlooking the Dye-Making Ability of Aryl Diazonium Salts

• The Mistake: Students match Aryl diazonium salts (iv) with only (d) Conversion to alcohols and forget the coupling reaction that makes dyes. …