Acidity of Phenols
Contents
• Resonance structures of phenol and phenoxide
• Effect of substituents on acidity of
phenol
• Qualitative tests for phenols
• Structure and uses of phenol,
cresols, resorcinol, naphthols
Learning Objectives
At the
end of this lecture, the student will be able to
Qualitative Tests
• Action with sodium hydrodide
• Liebermann’s reaction
• Phthalein test
• Azo dye formation
• Scotten Baumann reaction
• Phenol dissolves in sodium hydroxide
Experiment |
Observation |
Inference |
To one |
Violet |
Presence |
Liebermann’s |
A deep |
Characteristic |
Phthalein test: About 2 drops of melted phenol is mixed with |
Pink solution |
Due to formation of phenolphthalein |
Azo-dye formation: Dissolved two drops of aniline in |
A red colour |
Formation of azo dye |
Scotten-Baumann reaction: Dissolved about 0.25g of phenol |
A white precipitate is formed |
Formation of phenyl benzoate |
Structure and Uses of Phenol
• Phenols are widely used in
household products and as intermediates for industrial synthesis
• used (in low concentrations) as a disinfectant
in household cleaners and in mouthwash
Structure and Uses Cresols
• Different isomers are present

• Antibacterial and insecticidal
properties
Structure and Uses of
Resorcinol
• To treat acne, seborrheic
dermatitis, eczema, psoriasis, and other skin disorders
• To treat corns and warts
• Resorcinol works by helping to remove hard,
scaly, or roughened skin
Structure and Uses of
Naphthols
• 2-Naphthol is a
widely used as intermediate for the production of dyes and other compounds
Summary
• Acidity of phenol is explained by
difference in the resonance stabilization of phenol and phenoxide ion
• Electron withdrawing groups
increases the acidity of phenol
• Electron donating groups decreases’
the acidity of phenol
• Liebermann’s reaction and Phthalein
test are characteristic reactions of phenol
• Phenol is used (in low concentrations) as a
disinfectant in household cleaners and in mouthwash
• Cresol has antibacterial and
insecticidal properties
• Resorcinol is used to
treat acne, seborrheic dermatitis, eczema, psoriasis, and
other skin disorders
• 2-Naphthol is a
widely used as intermediate for the production of dyes and other compounds
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