Asked in PMC Practice Test 11 (2021) 2021Moderate

Which of the following major product(s) is formed when phenol reacts with sulphuric acid at 100 °C?

Correct answer: B. Para-hydroxy benzene sulphonic acid

  • A. Ortho-hydroxy benzene sulphonic acid
  • B. Para-hydroxy benzene sulphonic acid
  • C. Meta-hydroxybenzene sulphonic acid
  • D. Both a and b

Explanation

The reaction of phenol with concentrated sulphuric acid is thermodynamically controlled. at 25 Celsius the Ortho product predominates while at 100 Celsius the Para product is the major product.

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About Phenols

Phenols contain a hydroxyl group directly bonded to an aromatic ring, making them more acidic than alcohols because the phenoxide ion is resonance-stabilised. Reactions include ionisation with bases, electrophilic substitution, bromination, nitration and oxidation, with attention to the difference between phenols and aliphatic alcohols.

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