1.Nucleophilic Addition Reactions:
A.Addition of Hydrogen Cyanide (HCN):
Aldehydes and ketones react with HCN to form cyanohydrins.
Example: Acetone + HCN → Acetone cyanohydrin (CH₃COHCN).
B.Addition of Alcohols (Hemiacetal and Acetal Formation):
Aldehydes react with alcohols in the presence of an acid catalyst to form hemiacetals and subsequently acetals.
Example: Ethanal + Methanol → Ethanal hemiacetal → Acetal.
C.Addition of Amines (Imine Formation):
Reaction with primary amines (RNH₂) yields imines (Schiff bases).
Example: Acetone + Methylamine → Imine.
2.Oxidation Reactions:
D.Oxidation to Carboxylic Acids:
Aldehydes are easily oxidized to carboxylic acids using oxidizing agents like KMnO₄, K₂Cr₂O₇, or Tollens' reagent.
Example: Ethanal (CH₃CHO) oxidized to acetic acid (CH₃COOH).
E.Mild Oxidation (Tollens' and Fehling’s Test):
Tollens' test: Aldehydes react with Tollens' reagent (AgNO₃ in ammonia) to form a silver mirror.
Fehling's test: Aldehydes reduce Fehling's solution to a red precipitate of Cu₂O.
3.Reduction Reactions:
F.Reduction to Alcohols:
Aldehydes and ketones can be reduced to primary and secondary alcohols respectively using reducing agents like NaBH₄ or LiAlH₄.
Example: Propanone (CH₃COCH₃) reduced to isopropanol (CH₃CHOHCH₃).
G.Catalytic Hydrogenation:
Reduction using H₂ gas in the presence of a catalyst (e.g., Pt, Pd) to form alcohols.
4.Aldol Condensation:
Aldehydes and ketones containing α-hydrogens undergo aldol condensation in the presence of a base to form β-hydroxy aldehydes or ketones, which can further dehydrate to α,β-unsaturated carbonyl compounds.
Example: Two molecules of acetaldehyde react to form 3-hydroxybutanal (aldol) which can dehydrate to crotonaldehyde.
5.Cannizzaro Reaction:
Aldehydes without α-hydrogens react with a strong base (e.g., NaOH) to produce a mixture of a carboxylic acid and an alcohol.
Example: Formaldehyde (HCHO) in NaOH → methanol (CH₃OH) + formic acid (HCOOH).
6.Grignard Reaction:
Aldehydes and ketones react with Grignard reagents (RMgX) to form alcohols.
Example: Acetone + Methylmagnesium bromide → 2-Methyl-2-propanol.
7.Haloform Reaction:
Methyl ketones (CH₃COR) react with halogens in the presence of a base to produce a haloform (CHX₃, where X is a halogen) and a carboxylate ion.
Example: Acetone + I₂ + NaOH → Iodoform (CHI₃) + Sodium acetate (CH₃COONa).