CHEMISTRY TEXTBOOK

d. Reactions of phenols : Phenol undergoes

electrophilic substitution reactions more readily

as compared to benzene. The -OH group in

phenol is ring activating and an ortho-/para-

directing group.

i. Halogentaion of phenol: Phenol reacts

with aqueous solution of bromine to give

2,4,6 -tribromophenol (chlorine reacts in the

same way.)

If the reaction is carried out in a solvent of

lower polarity than water, such as CHCl 3 ,

CCl 4 or CS 2 , a mixture of ortho- and para-

bromophenol is formed.

ii. Nitration of phenol : Phenol reacts with
dilute nitric acid at low temperature to give
mixture of ortho- and para-nitrophenol.

Phenol reacts with concentrated nitric acid to
form 2, 4, 6-trinitrophenol (picric acid)

iii. Sulfonation of phenol : Phenol reacts with

concentrated sulfuric acid at room temperature

to give o-phenolsulfonic acid and at 373K,

p-phenol sulfonic acid

OH

OH

HO-SO 3 H SO 3 H

HO-SO 3 H

293K

373K

+ OH

SO 3 H

(o- Phenolsulfonic acid)

(p- Phenolsulfonic acid)

iv. Reimer-Tiemann Reaction : When phenol

is treated with chloroform in aqueous sodium

hydroxide solution followed by hydrolysis with

acid, salicylaldehyde is formed. This reaction

is known as Reimer-Tiemann reaction.

OH ONa

⊕

CHCl 2

aq. NaOH

CHCl 3 NaOH

(Phenol) Intermediate

ONa

⊕

CHO

OH

CHO

H 3 O⊕

(Salicyaldehyde)

If carbon tetrachloride is used in place of

chloroform, salicylic acid is formed.

v. Kolbe reaction : The treatment of sodium

phenoxide with carbon dioxide at 398 K under

pressure of 6 atm followed by acid- hydrolysis,

salicylic acid (o-hydroxybenzoic acid) is

formed. This reaction is known as Kolbe’s

reaction

ONa

⊕

+ CO 2 6 atm398K

OH

COONa

H 3 O⊕

(Sodium

Phenoxide)

(Sodium

salicylate) OH

COOH

(Salicylic acid)

OH

+ 3Br 2 H^2 O

OH

Br

Br Br

+ 3HBr

(Phenol) (2,4,6-tribromophenol)

OH

+ Br 2 CS 2

Low

temperature

OH

Br

+

OH

Br

+ HBr

Major product

(Phenol) (o- bromophenol)

(p- bromophenol)

OH

+ HO-NO 2

OH

NO 2

+

OH

(Phenol) (o- nitrophenol) NO 2

(p- nitrophenol)

OH

• 3HO-NO (^2) H
  2 SO 4
  Conc.
  OH
  NO 2
  O 2 N NO 2


• 3H 2 O
  (Phenol)
  (picric acid)
  (Phenol)