Aldehydes, Ketones and Carboxylic Acids

• Introduction & Structure

  • Carbonyl Group ($\text{C}=\text{O}$)
    • $\text{sp}^2$ hybridized carbon
    • Trigonal planar geometry
    • Polar nature (electronegative oxygen)
  • Nomenclature
    • Common names vs. IUPAC names
    • Suffixes: -al (aldehydes), -one (ketones), -oic acid (carboxylic acids)

• Preparation of Aldehydes and Ketones

  • Oxidation of Alcohols
    • Primary alcohols to aldehydes
    • Secondary alcohols to ketones
  • Dehydrogenation of Alcohols
    • Catalytic action of $\text{Cu}$ at $573\text{ K}$
  • Hydrolysis of Gem-dihalides
  • Ozonolysis of Alkenes
  • Preparation of Aldehydes only
    • Rosenmund Reduction ($\text{H}_2/\text{Pd-BaSO}_4$)
    • Stephen Reaction ($\text{SnCl}_2/\text{HCl}$ then hydrolysis)
    • Etard Reaction ($\text{CrO}_2\text{Cl}_2$ for toluene to benzaldehyde)
  • Preparation of Ketones only
    • Acylation of Arenes (Friedel-Crafts reaction)
    • Reaction of acyl chlorides with Grignard Reagents

• Preparation of Carboxylic Acids

  • Oxidation of Primary Alcohols and Aldehydes
  • Oxidation of Alkylbenzenes (using alkaline $\text{KMnO}_4$)
  • Hydrolysis of Nitriles and Amides
  • Using Grignard Reagents (reaction with dry ice/carbon dioxide)
  • Hydrolysis of Acyl Halides and Anhydrides

• Physical Properties

  • Boiling Points
    • Higher than hydrocarbons/ethers due to dipole-dipole interactions
    • Lower than alcohols (no intermolecular H-bonding in aldehydes/ketones, except carboxylic acids)
  • Solubility
    • Lower members are miscible in water due to hydrogen bonding
    • Solubility decreases with increasing alkyl chain length

• Chemical Reactions of Aldehydes & Ketones

  • Nucleophilic Addition Reactions
    • Addition of Hydrogen Cyanide ($\text{HCN}$)
    • Addition of Sodium Hydrogen Sulphite ($\text{NaHSO}_3$)
    • Addition of Grignard Reagents ($\text{RMgX}$)
    • Addition of Alcohols (formation of hemiacetals and acetals)
    • Addition of Ammonia derivatives (2,4-DNP test, hydrazones, semicarbazones)
  • Reduction
    • Reduction to alcohols ($\text{LiAlH}_4$, $\text{NaBH}_4$)
    • Reduction to hydrocarbons: Clemmensen Reduction ($\Zn-\text{Hg}/\text{HCl}$) and Wolff-Kishner Reduction ($\text{NH}_2\text{NH}_2/\text{KOH}$)
  • Oxidation
    • Aldehydes are easily oxidized to carboxylic acids
    • Tollens' Test (Silver mirror test for aldehydes)
    • Fehling's Test (Red precipitate for aliphatic aldehydes)
  • Reactions involving $\alpha$-Hydrogens
    • Aldol Condensation (dilute alkali catalyst)
    • Crossed Aldol Condensation
    • Cannizzaro Reaction (disproportionation without $\alpha$-hydrogen)
  • Other Reactions
    • Haloform Reaction (Iodoform test for methyl ketones)

• Chemical Reactions of Carboxylic Acids

  • Acidity
    • Reaction with metals and alkalies
    • Effect of substituents on acid strength (Electron-withdrawing vs. electron-donating groups)
  • Reactions Involving $\text{C}-\text{OH}$ Bond Cleavage
    • Formation of anhydride (with $\text{P}_2\text{O}_5$)
    • Esterification (Fischer esterification with alcohols)
    • Reaction with $\text{PCl}_5$, $\text{PCl}_3$, and $\text{SOCl}_2$
    • Reaction with Ammonia (formation of amides)
  • Reactions Involving Carboxyl Group
    • Decarboxylation (heating with sodalime)
    • Hine-Volhard-Zelinsky (HVZ) Reaction ($\alpha$-halogenation)

• Important Named Reactions Summary

  • Rosenmund Reduction
  • Stephen Reaction
  • Etard Reaction
  • Gattermann-Koch Reaction
  • Aldol Condensation
  • Cannizzaro Reaction
  • Clemmensen Reduction
  • Wolff-Kishner Reduction
  • HVZ Reaction