Alcohols – The Hydroxyl Compounds

📚 Key Concepts

🔹 Real-Life Example

When you use hand sanitizer, you’re using ethyl alcohol (ethanol). The “alcohol” in alcoholic beverages is the same ethanol, but the methyl alcohol (methanol) used in laboratories is highly poisonous. Both are alcohols but with very different effects on the human body!

Alcohols: Organic compounds containing one or more hydroxyl (-OH) functional groups attached to carbon atoms. They are derivatives of hydrocarbons where one or more hydrogen atoms are replaced by -OH groups.

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🧪 Properties and Classification

🔸 Classification of Alcohols

Based on number of -OH groups:

  • Monohydric: One -OH group (CH₃OH, C₂H₅OH)
  • Dihydric: Two -OH groups (Ethylene glycol)
  • Trihydric: Three -OH groups (Glycerol)

Based on carbon attachment:

  • Primary (1°): -OH attached to primary carbon
  • Secondary (2°): -OH attached to secondary carbon
  • Tertiary (3°): -OH attached to tertiary carbon

🔸 Physical Properties

  • Boiling points: Higher than corresponding alkanes (due to hydrogen bonding)
  • Solubility: Lower alcohols are soluble in water
  • Intermolecular forces: Hydrogen bonds between -OH groups

🔸 Chemical Properties

Reaction with Sodium: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑

Oxidation:

  • Primary alcohol → Aldehyde → Carboxylic acid
  • Secondary alcohol → Ketone
  • Tertiary alcohol → No easy oxidation

🧪 Important Alcohols

🔸 Methanol (CH₃OH)

Properties:

  • Colorless liquid
  • Highly toxic (causes blindness, death)
  • Miscible with water

Uses:

  • Solvent in laboratories
  • Fuel additive
  • Manufacturing formaldehyde

🔸 Ethanol (C₂H₅OH)

Properties:

  • Colorless liquid
  • Pleasant smell
  • Miscible with water
  • Depressant drug

Preparation: Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (Glucose converts to ethanol using yeast)

Uses:

  • Alcoholic beverages
  • Antiseptic and disinfectant
  • Solvent for medicines
  • Fuel (gasohol)

🔍 Advanced: Denatured Alcohol

Ethanol for industrial use is mixed with poisonous methanol to make it unfit for drinking. This prevents misuse and avoids high taxes on beverage alcohol.