Alcohols and Phenols

Alcohols

Alcohols: compounds containing an -OH group bonded to a hydrocarbon radical.

• Monohydric: methanol, ethanol.
• Dihydric: ethylene glycol.
• Trihydric: glycerol.

Phenol C₆H₅OH: the hydroxyl group is bonded directly to the benzene ring.

Oxidation of alcohols

1. Primary alcohol R-CH₂OH
2. Oxidized [O]: aldehyde R-CHO
3. Oxidized again [O]: carboxylic acid R-COOH

Primary alcohol → aldehyde → acid. Secondary alcohol → ketone.

Properties of alcohols

• React with Na to release H₂: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑.
• Undergo dehydration: ether at 140 °C, alkene at 170 °C.
• Form esters with carboxylic acids.

Phenol

• Phenol is a weak acid. Phenol reacts with NaOH, alcohol does not.
• Phenol + FeCl₃: violet colour.
• With bromine water, a white precipitate of 2,4,6-tribromophenol forms.
• Carbolic acid, an antiseptic. Phenol-formaldehyde resins (plastics) are made using it.

Qualitative reaction and preparation

• Glycerol + Cu(OH)₂: blue solution. Cu(OH)₂ must be freshly precipitated (qualitative reaction for polyhydric alcohols).
• Ethanol: fermentation of glucose (C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂) and hydration of ethylene.
• Methanol is a strong poison (blindness, death).
• Alcohols have high boiling points due to hydrogen bonding.