Here’s a clear explanation of the properties of phenols, divided into physical and chemical:
1. Physical Properties
- State and Appearance: Phenol is a colorless crystalline solid, but it often turns pink on exposure to air due to oxidation.
- Odor: Has a characteristic medicinal or antiseptic smell.
- Solubility: Moderately soluble in water because of hydrogen bonding. Solubility decreases with increase in the size of the aromatic group.
- Boiling Point: Higher than hydrocarbons and ethers of similar mass due to hydrogen bonding between molecules.
- Taste and Touch: Has a burning taste and is corrosive, causing blisters on skin.
2. Chemical Properties
- Acidic Nature:
- Phenols are weak acids (stronger than alcohols but weaker than carboxylic acids).
- They form salts with strong bases like sodium hydroxide but not with weaker bases like sodium bicarbonate.
- Electrophilic Substitution Reactions:
- The –OH group activates the benzene ring, mainly at ortho and para positions.
- They undergo halogenation, nitration, and sulphonation more easily than benzene.
- Special Reactions:
- Reimer–Tiemann reaction produces salicylaldehyde.
- Kolbe’s reaction produces salicylic acid.
- Oxidation: Phenols are easily oxidized to colored compounds and can form quinones under strong oxidizing conditions.
- Ester and Ether Formation: Phenols can form esters with acids/acid derivatives and ethers through Williamson’s synthesis.
Summary:
Phenols are crystalline solids with an antiseptic odor, soluble in water due to hydrogen bonding, and have higher boiling points. Chemically, they are weakly acidic, undergo electrophilic substitution easily, and participate in important reactions like Reimer–Tiemann and Kolbe’s.