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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.