Properties of Alcohols and Phenols

• Key Understanding:
  • Alcohols and phenols have distinct physical and chemical properties due to their functional groups.

Boiling Points

• Comparison of Alcohols and Alkanes:

  • Boiling Points: Higher in alcohols than in alkanes of similar molecular mass due to hydrogen bonding.
  • Effect of Length: As carbon chain length increases, boiling points rise.

• Intermolecular Forces:

  • Alcohols exhibit hydrogen bonding (stronger than van der Waals forces in alkanes).
  • Higher energy required to separate alcohol molecules due to stronger intermolecular forces.

Hydrogen Bonding

• Definition: Interaction between hydrogen atoms and electronegative elements (O, N, F).
• Example in Alcohols: Hydrogen bonds form between the -OH groups of alcohols, contributing to their higher boiling points.

Solubility in Water

• Small Alcohols: Completely soluble due to hydrogen bonding with water molecules.
• Longer Chains: Decreased solubility as hydrophobic hydrocarbon tail grows (+4 carbon atoms forms two layers in a solution).

Acid/Base Properties of Alcohols

• General Characteristics: Weak acids and bases, can donate protons (H+).
• Order of Acidity: Water > Primary > Secondary > Tertiary alcohols.
• Example Reaction: Alcohols react with bases to form alkoxide ions.

Acidity of Phenols

• Stability of Phenoxide Ion: The delocalization of the negative charge contributes to the acidity of phenol compared to alcohols.
• Resonance: Phenol's acidity stems from the stabilized phenoxide ion through resonance.
• Comparative Strength: Phenols are significantly more acidic than equivalent alcohols (over a million times stronger).

Factors Influencing Acidity

• Electron-Withdrawing Groups: Increase the acidity of phenols by stabilizing the phenoxide ion.
• Inductive and Resonance Effects: These effects determine the acidity of substituted phenols in comparison to phenol itself.

Chemical Reactions of Alcohols

Formation Reactions

• From Alkyl Halides: SN2 reactions using OH- as a nucleophile.
• From Alkenes: Director hydration methods like oxymercuration and hydroboration-oxidation yield alcohol.
• Grignard Reaction: Reactions involving Grignard reagents lead to alcohol formation with carbon chain length enlargement.

Dehydration of Alcohols

• Mechanism: Alcohols lose water to form alkenes (E1 or E2 mechanisms).
  • Primary > Secondary > Tertiary alcohols depending on temperature and substrate.
• Catalysis: Strong acids catalyze the reaction and can influence product formation.

Conversion to Alkyl Halides

• Reactivity Order: 3° > 2° > 1°.
• Reagents Used: HI > HBr > HCl for SN1 reactions in alcohols.

Oxidation of Alcohols

• Primary: Converted to aldehydes or carboxylic acids.
• Secondary: Oxidized to ketones.
• Tertiary: Generally do not undergo oxidation.
• Reagents: Chromic acid, PCC, Dess-Martin periodinane (DMP) facilitate the oxidation reaction.

Protection and Deprotection of Alcohols

• Importance: Protect functional groups in multi-step organic synthesis.
• Common Method: Formation of silyl ethers for protecting alcohols using chlorotrialkylsilane.
• Steps: Protect -> React -> Deprotect.

Phenols

Industrial Preparation of Phenols

• Dow Process: Hydrolysis of chlorobenzene with base produces sodium phenoxide, which upon acidification yields phenol.
• Cumene Process: Oxidation of isopropylbenzene (cumene) leads to phenol production through hydrolysis of intermediate.

Applications of Phenols

• Antiseptics and Disinfectants: First widely used antiseptic was phenol itself.
• Safety: Phenol is toxic; safer alternatives such as 4-hexylresorcinol are now sought after.
• BPA Concerns: Bisphenol A is associated with hormonal effects and environmental pollution from plastic waste.