Topic 32: Hydroxy Compounds

Question 1

Definitions I:
(a) Acyl chloride
(b) Phenol
(c) Azo compound

Answer 1

Definitions I:
(a) Compound with -COCl group, e.g., CH₃COCl.
(b) Aromatic compound with -OH on benzene, e.g., C₆H₅OH.
(c) Compound with -N=N- group, e.g., from phenol + diazonium.

Question 2

Compare the acidities of H₂O, C₆H₅OH, and CH₃CH₂OH with reasoning. [3 Marks]

Answer 2

Phenol > H₂O > ethanol (1 mark)
Phenol: delocalised anion, H₂O: no resonance (1 mark)
Ethanol: +I effect weakens acidity (1 mark)

Question 2

Write equations for:
(a) Ethanol + CH₃COCl [1 Mark]
(b) Phenol + NaOH(aq) [1 Mark]

Answer 2

(a) CH₃CH₂OH + CH₃COCl → CH₃COOCH₂CH₃ + HCl (1 mark)
(b) C₆H₅OH + NaOH → C₆H₅ONa + H₂O (1 mark)

Question 3

Predict the products of phenol with dilute HNO₃ at room temp. [2 Marks]

Answer 3

C₆H₅OH + HNO₃ → C₆H₄(OH)NO₂ (1 mark)
2-nitrophenol and 4-nitrophenol (1 mark)

Question 4

In a lab, phenylamine forms phenol. Write the equation and conditions. [2 Marks]

Answer 4

C₆H₅NH₂ + HNO₂ → C₆H₅N₂⁺ + 2H₂O (<10°C), then + H₂O → C₆H₅OH (warm) (1 mark)
NaNO₂/HCl, then heat (1 mark)

Question 5

Why is phenol more acidic than ethanol? [2 Marks]

Answer 5

Phenol: -OH delocalises into ring, stabilises C₆H₅O⁻ (1 mark)
Ethanol: no delocalisation, less acidic (1 mark)

Question 6

Describe the bromination of phenol with Br₂(aq) and name the product. [2 Marks]

Answer 6

C₆H₅OH + 3Br₂ → C₆H₂(OH)Br₃ + 3HBr (aq) (1 mark)
2,4,6-Tribromophenol (1 mark)

Question 7

In a dye test, phenol reacts with a diazonium salt in NaOH. Write the equation. [2 Marks]

Answer 7

C₆H₅OH + C₆H₅N₂⁺ → C₆H₅N=NC₆H₄OH + H⁺ (NaOH) (1 mark)
Azo dye formed (1 mark)

Question 8

Why does phenol nitrate with dilute HNO₃ but benzene needs concentrated HNO₃? [2 Marks]

Answer 8

Phenol: -OH activates ring, dilute HNO₃ sufficient (1 mark)
Benzene: no activation, needs concentrated HNO₃ (1 mark)

Question 9

Predict the reaction of naphthol with Br₂(aq) based on phenol’s chemistry. [2 Marks]

Answer 9

Naphthol + 3Br₂ → tribromonaphthol + 3HBr (aq) (1 mark)
Similar to phenol, 2,4,6-positions (1 mark)

Question 10

Explain how phenol directs substitution to 2-, 4-, 6-positions with Br₂. [2 Marks]

Answer 10

-OH donates electrons, activates ortho/para (1 mark)
2-, 4-, 6-positions substituted (1 mark)

Question 11

Describe the synthesis of phenol from phenylamine and its reaction with Na(s). [3 Marks]

Answer 11

C₆H₅NH₂ + NaNO₂ + HCl → C₆H₅N₂⁺ (<10°C), then + H₂O → C₆H₅OH (warm) (1 mark)
C₆H₅OH + Na → C₆H₅ONa + ½H₂ (1 mark)
Diazonium hydrolysis, then base reaction (1 mark)