Phenol — Reactions

• Kolbe's reaction and Reimer-Tiemann reaction as unique reactions of phenol.
• Coupling of phenol with diazonium salts to give azo dyes.
• Why phenol is more acidic than alcohols (resonance stabilisation of phenoxide).
• Electrophilic aromatic substitution (EAS) on phenol: ring activation by −OH.

Level 1 — Acidic nature of phenol

Phenol vs alcohol acidity:

• Phenol pKₐ ≈ 10; ethanol pKₐ ≈ 16. Phenol is ~10⁶ times more acidic than ethanol.
• Reason: Phenoxide ion (C₆H₅O⁻) stabilised by resonance — negative charge delocalised over ring. Alkoxide (RO⁻) has no such delocalisation.
• Test: Phenol reacts with NaHCO₃? No (pKₐ 10 > pKₐ carbonic acid 6.3 — wait: phenol does NOT liberate CO₂ from NaHCO₃; only strong acids like carboxylic acids do. Phenol dissolves in NaOH solution.

Ring activation: −OH is a strong ortho/para director → makes benzene ring electron-rich → EAS very fast (phenol brominates in cold water, no catalyst needed).

Level 2 — Named reactions of phenol

Kolbe's reaction (Kolbe–Schmitt): Phenol + CO₂ (under pressure) + NaOH → sodium salicylate → salicylic acid (on acidification). Used to make aspirin precursor. Carboxylation at ortho position.

C₆H₅ONa + CO₂ → (pressure, 125°C) → C₆H₄(OH)(COONa) → (H⁺) → salicylic acid.

Reimer-Tiemann reaction: Phenol + CHCl₃ + NaOH → salicylaldehyde (2-hydroxybenzaldehyde) — CHO introduced at ortho position. Mechanism: dichlorocarbene (:CCl₂) intermediate.

Coupling with diazonium salt (azo coupling): C₆H₅−N₂⁺Cl⁻ + phenol (in alkaline solution) → p-hydroxyazobenzene (orange/red azo dye). Electrophile: ArN₂⁺; attacks electron-rich para position of phenol ring. Basis of azo dye industry — majority of synthetic dyes.

JEE tip: Kolbe = CO₂ (carboxyl group); Reimer-Tiemann = CHCl₃ (aldehyde group). Both give ortho product predominantly.

NCERT spotlight — Phenol vs alcohol reactivity

Phenol is more reactive toward EAS than benzene because −OH donates electrons to ring by resonance. Phenol does not undergo SN reactions like alcohols because C−O bond in phenol has partial double bond character (resonance). Phenol undergoes FeCl₃ test: violet/purple colour with ferric chloride — test for phenol.

Bakelite: Phenol + formaldehyde → condensation polymer — one of earliest synthetic plastics. Still used in electrical fittings, brake pads. Application of phenol chemistry.

Explain why phenol reacts with Br₂ water but benzene does not, and predict the product.

Step 1 — Benzene + Br₂ water: no reaction (Br₂ is weak electrophile; benzene ring not activated).
Step 2 — Phenol: −OH group strongly activates ring by resonance (lone pair on O donates into ring).
Step 3 — Ring electron density especially high at ortho and para positions.
Step 4 — Br₂ attacks ortho and para positions.
Step 5 — All three positions (2, 4, 6) are ortho/para to −OH → all three bromo positions filled.
Step 6 — Product: 2,4,6-tribromophenol (white precipitate) + 3HBr.
Equation: C₆H₅OH + 3Br₂ → C₆H₂Br₃OH + 3HBr ✓.

Applications — antiseptics and dyes

Phenol (carbolic acid): first surgical antiseptic (Lister). Chlorinated phenols (TCP, Dettol) are antiseptics. Azo dyes — most commercial fabric dyes (Red, Orange, Yellow food colours). Salicylic acid (from Kolbe) → aspirin (acetylsalicylic acid).

• Give two differences between phenol and ethanol (acidic nature + ring reactivity).
• What are the products of Kolbe's reaction? Name a commercial application.
• Why does phenol give 2,4,6-tribromophenol instead of monobromophenol?

Open the Practice tab for graded questions on Phenol Reactions.

• Use the platform-native live simulation or PhET-style tool for this topic (number line, Venn, physics playground, molecule builder, sensor dashboard, etc.).
• Mirror / body / home activity: physically do the concept (count objects, measure, role-play) and photograph or describe for portfolio.
• Voice or text reflection with AI Mentor: explain the concept to a younger student or family member.

• "Explain this concept to a Class 6 student using one real example from an Indian home, school, market, or festival."
• "What is one common mistake students make here, and how would you catch yourself making it?"
• Stretch: "How does this connect to coding, robotics, money, health, environment, or a future career?"

• Complete the core practice + one extension activity (photo, table, short reflection, or mini-project) for base XP + topic badge.
• 5-7 day streak or family discussion note = multiplier + visible artifact in parent/principal dashboard.
• Best real-world application stories (anonymised) featured on class or national leaderboard.

• One hands-on project or measurement using the Drishti kit or household items that makes the concept physical.
• Direct link to at least one Future Skill track (Money Management, Green Tech, Cyber Defenders, Micro-Entrepreneurship, AI Mastery, Sustainable Living, Personality Development).
• Coding extension where relevant (simple script, simulation, or data logging).

This material emphasises experiential "learning by doing", competency (apply/create/analyse), vocational exposure, critical thinking, and multidisciplinary connections. Designed to feed live worlds, AI Mentor (with memory), gamification, robotics, parent analytics, and future skills — not just exam prep.

Portfolio Evidence Idea: Your photo/table/reflection/project + one sentence on "How this helps me in real life or a possible future path."

Open the Practice tab for aligned questions (easy/medium/hard + case-based) with full AI scaffolding.

See curriculum for cross-links and the full future-skills/robotics chapters.