Organic conversion

Benzene to phenol

2 steps: substitution, then substitution

Class 12, Chapter 6 Haloalkanes and Haloarenes

BenzeneC₆H₆Arene
Step 1
Cl₂, anhydrous FeCl₃
i
Electrophilic substitution; the Lewis acid polarises Cl₂.
ChlorobenzeneC₆H₅ClHaloarene
Step 2
(i) NaOH, 623 K, 300 atm (ii) H⁺
i
Haloarenes are unreactive to NaOH under mild conditions; this needs high temperature and pressure.
PhenolC₆H₅OHPhenol

Alternative routes (3)

Benzene → Cumene → Phenol
1. Benzene to cumene: CH₃CH₂CH₂Cl, anhydrous AlCl₃.
2. Cumene to phenol: (i) O₂ (ii) H₃O⁺.
Benzene → Benzene sulphonic acid → Phenol
1. Benzene to benzene sulphonic acid: fuming H₂SO₄ (oleum).
2. Benzene sulphonic acid to phenol: (i) NaOH (molten), heat (ii) H⁺.
Benzene → Nitrobenzene → Aniline → Benzene diazonium chloride → Phenol
1. Benzene to nitrobenzene: conc. HNO₃ + conc. H₂SO₄, 323 to 333 K.
2. Nitrobenzene to aniline: Sn + conc. HCl.
3. Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
4. Benzene diazonium chloride to phenol: H₂O, warm.

Why these reagents

Reagent and reason, step by step

Step 1: Benzene to chlorobenzene: Cl₂, anhydrous FeCl₃ Electrophilic substitution; the Lewis acid polarises Cl₂.
Step 2: Chlorobenzene to phenol: (i) NaOH, 623 K, 300 atm (ii) H⁺ Haloarenes are unreactive to NaOH under mild conditions; this needs high temperature and pressure.

Questions

How many steps does it take to convert benzene to phenol?

2 steps: Benzene, then chlorobenzene, then phenol.

Which named reaction is used to convert benzene to phenol?

None of the steps has a name. They are substitution and substitution, so write the reagent and the condition for each step.

What is the reagent for step 1 of benzene to phenol?

Benzene to chlorobenzene: Cl₂, anhydrous FeCl₃. Electrophilic substitution; the Lewis acid polarises Cl₂.