Preparation and Reactions of Aldehydes and Ketones

Preparation of Aldehydes and Ketones

• Alcohols can be oxidized to produce aldehydes and ketones.
• Primary alcohols are oxidized to aldehydes, which can then be further oxidized to carboxylic acids.
• Secondary alcohols are oxidized to ketones.
• Oxidizing agents include KMnO₄ or K₂Cr₂O₇.

Reactions of Aldehydes & Ketones

• Oxidation: Aldehydes are easily oxidized to carboxylic acids, while ketones are resistant to oxidation.
• Haloform: Reaction of methyl ketones and aldehydes with halogen in the presence of base forms haloform.
• Reduction: Carbonyl groups (C=O) in aldehydes and ketones can be converted to methylene groups (CH₂) through Clemmensen reduction (Zn/Hg/conc. HCl) or Wolff-Kishner reduction (heat with hydrazine and KOH in high-boiling alcohol).
• Nucleophilic Addition to Carbonyl: Addition of cyanide, derivatives of ammonia (e.g., cyanides, hydrazines, hydroxylamines, semicarbazides, and 2,4-dinitrophenylhydrazones), and alcohols to the carbonyl group.
• Cannizzaro Reaction: A redox reaction where two molecules of an aldehyde, without α-hydrogens, are reacted using a hydroxide base to produce an alcohol and a carboxylic acid.
• Aldol Condensation: Dimerization of aldehydes containing α-hydrogen atoms in alkaline media to form β-hydroxyaldehydes.
• Addition of Grignard Reagents: Grignard reagents (RMgX) react with aldehydes and ketones to form larger alcohols.

1- Oxidation

• Aldehydes easily oxidized to carboxylic acids.
• Ketones resistant to oxidation.

2- Haloform Reaction

• Reaction of methyl ketones and aldehydes with halogen in base to form haloform (after C-C cleavage).
• The aldehyde/ketone must have CH₃CO– group.

3- Reduction

• Conversion of carbonyl groups (C=O) to methylene groups (CH₂) using Clemmensen or Wolff-Kishner reduction.
• Zn/Hg/conc. HCl or NH₂NH₂, KOH used.

Reduction of Aldehydes and Ketones

• Aldehydes: Reduced to primary alcohols

• Ketones: Reduced to secondary alcohols

• Reducing agents: LiAlH₄, NaBH₄, catalytic hydrogenation (Pd/H₂)

Nucleophilic Addition to Carbonyl

• Addition reactions to the carbonyl carbon of aldehydes and ketones, involving nucleophiles.
• Mechanism often involves protonation, nucleophilic attack, and deprotonation.

4i) Addition of Cyanide

• Reaction of aldehydes/ketones with cyanide (NaCN) followed by acid hydrolysis to yield cyanohydrins.

4ii) Addition of Derivatives of Ammonia

• Addition of hydrazine, hydroxylamine, semicarbazide, and 2,4-dinitrophenylhydrazine to carbonyls

4iii) Addition of Alcohols

• Reaction with alcohols in presence of acid to form hemiacetals and acetals.
• Reaction with alcohols in presence of base to form hemiacetals and ketals.

5- Cannizzaro Reaction

• A redox reaction of aldehydes without α-hydrogens in presence of base to yield alcohol and carboxylic acid.

6- Aldol Condensation

• Dimerization reaction of aldehydes containing α-hydrogens in alkaline conditions to produce β-hydroxyaldehydes.

7) Addition of Grignard reagents

• Grignard reagents (RMgX) react with aldehydes and ketones producing larger alcohols.

Amines

• An amine with one carbon attached to nitrogen is a primary amine.
• Two carbons attached to nitrogen is a secondary amine.
• Three carbons attached to nitrogen is a tertiary amine.
• Amines are more polar than alkanes but less polar than alcohols.

Preparation of Amines (by Alkylation of Ammonia and Reduction)

• Alkylation of ammonia with alkyl halides forms amines.
• Acid amides can be reduced to amines.

Inductive Effects and Basicity

• Electron-donating groups increase basicity of amines.
• Electron-withdrawing groups decrease basicity.

This quiz covers the preparation methods and chemical reactions of aldehydes and ketones. It includes oxidation processes, nucleophilic additions, and specific reagents used in these reactions. Test your understanding of these important organic compounds and their transformations.