1. Acidic Nature
- Phenols are weak acids.
- They react with strong bases such as sodium hydroxide to form salts (phenoxides).
- They do not react with weaker bases like sodium bicarbonate.
2. Electrophilic Substitution Reactions
The –OH group activates the benzene ring, so substitution occurs mainly at the ortho and para positions.
- Halogenation: Phenols react with halogens (like bromine) to form tribromophenol, which is a white precipitate.
- Nitration: With dilute nitric acid, phenols give ortho- and para-nitrophenol. With concentrated nitric acid in presence of sulfuric acid, they form picric acid (trinitrophenol).
- Sulphonation: Reaction with concentrated sulfuric acid forms phenol sulphonic acids (ortho and para forms depending on temperature).
3. Reimer–Tiemann Reaction
- When phenol is treated with chloroform and a strong base, it produces salicylaldehyde (ortho-hydroxybenzaldehyde).
4. Kolbe’s Reaction
- When phenol is treated with carbon dioxide in the presence of sodium hydroxide under pressure, it forms salicylic acid (used in aspirin preparation).
5. Oxidation
- Phenols are easily oxidized. They give a violet color with neutral ferric chloride solution (a test for phenols).
- Strong oxidation leads to the formation of quinones.
6. Esterification
- Phenols react with acid chlorides or acid anhydrides to form esters, which are aromatic compounds with pleasant smells.
7. Williamson’s Synthesis
- Phenols react with alkyl halides in the presence of a base to form ethers.
In summary: Phenols show reactions due to their acidic nature, undergo electrophilic substitutions (halogenation, nitration, sulphonation), special reactions like Reimer–Tiemann and Kolbe’s, and also form esters and ethers.