Chapter 12: Aldehydes and Ketones

Carbonyl Compounds: Contain C=O group. Aldehydes (R-CHO) have carbonyl at the end. Ketones (R-CO-R) have carbonyl within the chain.

• Nomenclature:
  • Aldehydes: Alkanal (e.g., Methanal, Ethanal).
  • Ketones: Alkanone (e.g., Propanone, 2-Butanone).

Formaldehyde (Methanal)

• Lab: Oxidation of Methanol (Platinized Asbestos, 300°C).
• Industrial: Methanol + Air (Iron Oxide-Molybdenum Oxide, 500°C).

Acetaldehyde (Ethanal)

• Lab: Oxidation of Ethanol (Na2Cr2O7 + H2SO4).
• Industrial: Wacker Process (Oxidation of Ethylene with PdCl2/CuCl2).

Acetone (Propanone)

• Dry distillation of Calcium Acetate.
• Oxidation of Isopropyl Alcohol.

Carbonyl carbon is electrophilic due to polarity of C=O bond. Undergo Nucleophilic Addition Reactions.

• Base-Catalyzed: Nucleophile becomes stronger.
• Acid-Catalyzed: Carbonyl carbon becomes more electrophilic (protonation of oxygen).

• HCN: Forms Cyanohydrins. Mechanism involved base catalysis.
• Grignard Reagent:
  • HCHO -> 1° Alcohol.
  • Other Aldehydes -> 2° Alcohol.
  • Ketones -> 3° Alcohol.
• Sodium Bisulphite: Forms white crystalline adduct. Used for purification.
• Ammonia Derivatives: Condensation with NH2-G (e.g., Hydroxylamine -> Oximes, Hydrazine -> Hydrazones, Phenylhydrazine -> Phenylhydrazones, 2,4-DNPH -> Red/Yellow ppt).

Aldol Condensation

Aldehydes/Ketones with alpha-hydrogen react with dil. base to form Aldol (beta-hydroxy aldehyde/ketone). Dehydration gives alpha,beta-unsaturated carbonyl.

Cannizzaro's Reaction

Aldehydes with NO alpha-hydrogen (e.g., HCHO, Benzaldehyde) react with conc. base (50% NaOH). Self-oxidation-reduction (Disproportionation). One molecule oxidized to salt of acid, other reduced to alcohol.

• Oxidation:
  • Aldehydes -> Carboxylic Acids (Easily oxidized by weak agents like Tollen's/Fehling's).
  • Ketones -> Carboxylic Acids (Difficult, require strong agents, C-C bond cleavage).
  • Haloform Reaction (Iodoform Test): Methyl Ketones (CH3-CO-) or Methyl Carbinols (CH3-CH(OH)-) react with I2/NaOH to give yellow ppt of CHI3 (Iodoform). Used to distinguish Methanol/Ethanol and Methyl Ketones.
• Reduction:
  • NaBH4: Aldehydes -> 1° Alcohol, Ketones -> 2° Alcohol.
  • Catalytic Hydrogenation (Ni/Pd/Pt).

• 2,4-DNPH Test: Yellow/Red ppt (All Aldehydes and Ketones).
• Tollen's Test (Silver Mirror): Ag(NH3)2+. Aldehydes reduce it to Ag mirror. Ketones do not.
• Fehling's/Benedict's Test: Cu(II) complex. Aliphatic Aldehydes reduce it to red ppt (Cu2O). Ketones do not.
• Sodium Nitroprusside: Ketones give wine-red color.