Reactions of Phenols - Electrophilic Substitution - UNSOLVED PRACTICE SET
Chapter: Alcohols Phenols and Ethers | Topic: Reactions of Phenols Electrophilic Substitution
REACTIONS OF PHENOLS - ELECTROPHILIC SUBSTITUTION - UNSOLVED PRACTICE SET
Topic: Reactions of Phenols Electrophilic Substitution
Multiple Choice Questions
Q1. Phenol undergoes electrophilic substitution mainly at:
- Meta position
- Ortho and para positions
- All positions equally
- Only ortho position
Q2. The reaction of phenol with dilute HNO₃ gives:
- Only o-nitrophenol
- Only p-nitrophenol
- Mixture of oand p-nitrophenol
- 2,4,6-trinitrophenol
Q3. Phenol on sulphonation with conc. H₂SO₄ at 25°C gives mainly:
- o-hydroxybenzenesulphonic acid
- p-hydroxybenzenesulphonic acid
- Both ortho and para in equal amounts
- m-hydroxybenzenesulphonic acid
Q4. The Kolbe's reaction of phenol gives:
- Salicylaldehyde
- Salicylic acid
- p-hydroxybenzoic acid
- Aspirin
Q5. The Reimer-Tiemann reaction of phenol gives:
- Salicylaldehyde (o-hydroxybenzaldehyde)
- p-hydroxybenzaldehyde
- Benzoic acid
- Benzaldehyde
Q6. Phenol on reaction with phthalic anhydride in presence of conc. H₂SO₄ gives:
- Phenolphthalein
- Fluorescein
- Aspirin
- Bakelite
Short Answer Questions
Q7. Why does phenol undergo electrophilic substitution more readily than benzene? Explain using resonance structures.
Q8. Write the reaction of phenol with bromine water. Why is a white precipitate formed?
Q9. What is Kolbe's reaction? Write the reaction of phenol with CO₂ and NaOH at high temperature.
Q10. Why does phenol give ortho and para substituted products in electrophilic substitution rather than meta?
Q11. Write the reaction of phenol with formaldehyde in presence of acid or base. What is the product?
Q12. Your teacher shows you that phenol turns pink on exposure to air. What chemical change has occurred? Write the reaction.
Long Answer Questions
Q13. (a) Describe the mechanism of electrophilic substitution in phenol.
(b) Why does the -OH group activate the benzene ring towards electrophilic substitution?
(c) Why are ortho and para positions more activated than meta position?
(d) Compare the reactivity of phenol, anisole, and benzene towards electrophilic substitution.
Q14. (a) Describe the following reactions of phenol:
(i) Kolbe's reaction
(ii) Reimer-Tiemann reaction
(iii) Coupling with diazonium salts
Write the reactions and mention the conditions required.
(b) What is the mechanism of Reimer-Tiemann reaction? Why does it give ortho product predominantly?
Q15. (a) Describe the preparation of:
(i) Salicylic acid from phenol
(ii) Aspirin from salicylic acid
Write the reactions and conditions.
(b) Why is aspirin called a "wonder drug"? What are its medicinal uses and side effects?
Numerical / Application-Based Problems
Q16. The following reactions involve phenol:
Reaction 1: C₆H₅OH + 3Br₂(aq) → C₆H₂Br₃OH + 3HBr
Reaction 2: C₆H₅OH + NaOH + CO₂ (high T, high P) → Salicylic acid
Reaction 3: C₆H₅OH + CHCl₃ + NaOH → Salicylaldehyde
Reaction 4: C₆H₅OH + (CH₃CO)₂O → Aspirin
(a) Calculate the mass of 2,4,6-tribromophenol obtained from 9.4 g of phenol if the yield is 85%.
(b) For Reaction 2, calculate the mass of CO₂ required to produce 13.8 g of salicylic acid (C₇H₆O₃, molar mass = 138 g/mol).
(c) For Reaction 3, explain why the product is mainly ortho-substituted. What is the name of this reaction?
(d) For Reaction 4, if 13.8 g of salicylic acid reacts with excess acetic anhydride, calculate the theoretical yield of aspirin (C₉H₈O₄, molar mass = 180 g/mol).
(e) Aspirin is often buffered with Mg(OH)₂ or CaCO₃. Why? (Consider the acidic nature of aspirin.)
Q17. The following data relates to the production of phenol-formaldehyde resins:
| Component | Molar Mass (g/mol) | Amount Used (kg) |
|---|---|---|
| Phenol | 94 | 470 |
| Formaldehyde | 30 | 300 |
| Catalyst (acid/base) | - | 5 |
(a) Identify the limiting reagent in this reaction.
(b) Calculate the theoretical yield of Bakelite (assuming 1:1 molar ratio of phenol to formaldehyde for simplicity).
(c) In practice, excess formaldehyde is used to produce cross-linked Bakelite (novolac vs. resol). Explain the difference between novolac and resol in terms of structure.
(d) Calculate the mass of unreacted phenol if the reaction goes to 90% completion.
(e) Why is Bakelite called a thermosetting polymer? What property makes it suitable for electrical switches and handles?
Q18. In a school science exhibition, students display the uses of phenol derivatives.
(a) A student shows how phenolphthalein is used as an indicator. Write the reaction showing its synthesis from phenol and phthalic anhydride. Why does it turn pink in basic solution?
(b) Another student demonstrates the synthesis of bisphenol-A, used in making polycarbonate plastics and epoxy resins. It is made from phenol and acetone. Write the reaction. Why is bisphenol-A controversial? (Hint: Consider endocrine disruption.)
(c) A third student presents salicylic acid and its derivatives. Write the reaction showing the conversion of salicylic acid to methyl salicylate (wintergreen oil). Why does methyl salicylate have a minty smell?
(d) The students learn that picric acid (2,4,6-trinitrophenol) is used to treat burns. Why is it effective? What property of the phenoxide ion makes it useful?
(e) The teacher asks: "If you were designing a new polymer from phenol that is biodegradable, what structural modifications would you make?" Give your answer with reasoning.