Preparation and Properties of Phenols - UNSOLVED PRACTICE SET

Q7. Write the reaction for the preparation of phenol from cumene. What is this process called?

Q8. Why does phenol react with bromine water at room temperature, while benzene requires a catalyst?

Q9. Write the reaction of phenol with NaOH. Why does phenol react with NaOH while ethanol does not react with NaOH?

Q10. What is the Reimer-Tiemann reaction? Write the reaction of phenol with CHCl₃ and NaOH.

Q11. Why is phenol more acidic than alcohols but less acidic than carboxylic acids?

Q12. Your grandmother uses a phenol-based antiseptic for minor cuts. Why is phenol effective as an antiseptic? What concentration is typically used?

Q13. (a) Describe the preparation of phenol by:

(i) Cumene process

(ii) Dow process

(iii) From diazonium salts

Write the reactions for each method.

(b) Why is the cumene process preferred industrially?

Q14. (a) Describe the chemical properties of phenol with respect to:

(i) Electrophilic substitution reactions (halogenation, nitration, sulphonation)

(ii) Reaction with zinc dust

(iii) Oxidation

(iv) Reaction with FeCl₃

Write one reaction for each.

Q15. (a) Explain why phenol undergoes electrophilic substitution more readily than benzene.

(b) Why does phenol give ortho and para substituted products in electrophilic substitution?

(c) Compare the reactivity of phenol, benzene, and nitrobenzene towards electrophilic substitution. Give reasons.

Q16. The cumene process for phenol production involves the following steps:

Step 1: C₆H₆ + CH₃CH=CH₂ → C₆H₅CH(CH₃)₂ (cumene)

Step 2: C₆H₅CH(CH₃)₂ + O₂ → C₆H₅C(CH₃)₂OOH (cumene hydroperoxide)

Step 3: C₆H₅C(CH₃)₂OOH → C₆H₅OH + CH₃COCH₃ (phenol + acetone)

(a) Write the overall balanced equation for the process.

(b) If 120 g of benzene (molar mass = 78 g/mol) is used, calculate the theoretical yield of phenol (molar mass = 94 g/mol).

(c) In practice, 100 g of phenol is obtained. Calculate the percentage yield.

(d) Calculate the mass of acetone (molar mass = 58 g/mol) produced as a by-product.

(e) Why is this process economically favourable despite moderate yields? (Hint: Consider the by-product.)

Q17. The following reactions involve phenol and its derivatives:

Reaction 1: C₆H₅OH + Br₂(aq) → Product A

Reaction 2: C₆H₅OH + Br₂(CS₂) → Product B

Reaction 3: C₆H₅OH + CH₃COCl → Product C

Reaction 4: C₆H₅OH + NaOH + CH₃I → Product D

(a) Identify products A, B, C, and D.

(b) For Reaction 1, calculate the mass of Product A obtained from 9.4 g of phenol if the yield is 90%.

(c) For Reaction 2, why is CS₂ used as solvent instead of water? What is the major product?

(d) For Reaction 3, why is pyridine added to the reaction mixture?

(e) For Reaction 4, why is this method (Williamson ether synthesis) preferred over direct reaction of phenol with CH₃I?

Q18. In a school science project, students investigate the uses of phenol in everyday life.

(a) A student finds that her mother's salicylic acid face wash is made from phenol. Write the reaction showing the conversion of phenol to salicylic acid (Kolbe's reaction followed by acidification).

(b) Another student learns that Bakelite, the first plastic, is made from phenol and formaldehyde. Why does this reaction require a catalyst (acid or base)? What type of polymer is Bakelite?

(c) A third student discovers that 2,4-dinitrophenol (DNP) was once used as a weight-loss drug but was banned. Why was it banned? (Hint: Consider its effect on cellular respiration.)

(d) The students test phenol with FeCl₃ solution. A violet colour appears. What does this test indicate? Why do enols also give this test?

(e) The teacher asks: "If you were designing a new antiseptic that is less toxic than phenol but equally effective, what structural modifications would you make to the phenol molecule?" Give your answer with reasoning.