NCERT Example 9.5: 4-nitrotoluene to 2-bromobenzoic acidNCERT उदाहरण 9.5: 4-नाइट्रोटॉलूईन से 2-ब्रोमोबेन्ज़ोइक अम्लNCERT Example 9.5: 4-nitrotoluene to 2-bromobenzoic acid

Class 12 Chemistry · Chapter 9 · interactive diagram

Parts and what they mean

• 4-Nitrotoluene (start) (4-नाइट्रोटॉलूईन (प्रारंभ)) — CH₃ and NO₂ are para to each other.
• Br₂ / FeBr₃ (Br₂ / FeBr₃) — Electrophilic substitution ortho to CH₃ (= meta to NO₂).
• 2-Bromo-4-nitrotoluene (2-ब्रोमो-4-नाइट्रोटॉलूईन) — Br is now where we want it in the final acid (next to the carbon that will become COOH).
• Sn / HCl (Sn / HCl) — Reduces –NO₂ to –NH₂.
• 3-Bromo-4-methylaniline (3-ब्रोमो-4-मेथिलऐनिलीन) — A primary aromatic amine — ready for diazotisation.
• NaNO₂ + HCl, 273–278 K (NaNO₂ + HCl, 273–278 K) — Diazotisation.
• Diazonium salt (डाइऐज़ोनियम लवण) — The –N₂⁺Cl⁻ group can now simply be removed.
• H₃PO₂/H₂O or CH₃CH₂OH (H₃PO₂/H₂O या CH₃CH₂OH) — Replaces the diazo group by H (the trick to use NO₂/NH₂ only as a temporary director).
• 2-Bromotoluene (2-ब्रोमोटॉलूईन) — Br is ortho to CH₃.
• KMnO₄ / KOH, heat; then H₃O⁺ (KMnO₄ / KOH, गर्म; फिर H₃O⁺) — Side-chain oxidation: –CH₃ → –COO⁻K⁺, acidification gives –COOH.
• 2-Bromobenzoic acid (target) (2-ब्रोमोबेन्ज़ोइक अम्ल (लक्ष्य)) — COOH and Br are ortho to each other.

Steps

1. Bromination: CH₃ (o/p) and NO₂ (meta) both direct Br to the carbon next to CH₃.
2. Reduce NO₂ to NH₂ with Sn/HCl.
3. Diazotise the NH₂ at 273–278 K.
4. Remove the diazo group: replace it by H (H₃PO₂ or ethanol).
5. Oxidise CH₃ to COOH (KMnO₄/KOH, then acidify).

Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake