Preparation of Carbonyl compounds (Aldehydes and ketones)

Preparation of Carbonyl compounds Definition

• Preparation of carbonyl compounds refers to the chemical processes used to synthesize aldehydes and ketones, which are organic compounds containing the carbonyl group (C=O).

1. Oxidation of Alcohols

• Aldehydes:

  • Primary alcohols can be selectively oxidized to aldehydes using mild oxidizing agents such as pyridinium chlorochromate (PCC) or Dess-Martin periodinane.

• Ketones:

  • Secondary alcohols are oxidized to ketones using stronger oxidizing agents like potassium permanganate (KMnO₄), potassium dichromate (K₂Cr₂O₇), or chromium trioxide (CrO₃).

2. Reduction of Carboxylic Acids and Esters

• Aldehydes:

  • Carboxylic acids can be reduced to aldehydes using lithium aluminum hydride (LiAlH₄) followed by careful quenching, or diisobutylaluminum hydride (DIBAL-H).

• Ketones:

  • Esters are reduced to ketones by using reagents like lithium aluminum hydride (LiAlH₄) or sodium borohydride (NaBH₄).

3. Ozonolysis of Alkenes

• Both aldehydes and ketones can be synthesized by ozonolysis of alkenes.
• The double bond is cleaved using ozone (O₃) followed by a reductive work-up with zinc (Zn) and acetic acid (CH₃COOH) or dimethyl sulfide (DMS).

4. Friedel-Crafts Acylation

• Ketones:

  • Aromatic ketones are prepared via Friedel-Crafts acylation, where an aromatic ring reacts with an acyl halide in the presence of a Lewis acid catalyst like aluminum chloride (AlCl₃) or ferric chloride (FeCl₃).

5. Hydration of Alkynes

• Aldehydes:

  • Terminal alkynes are converted to aldehydes through hydroboration-oxidation, using a borane reagent followed by oxidation with hydrogen peroxide (H₂O₂).

• Ketones:

  • Internal alkynes are converted to ketones using a mercury(II) catalyst, such as mercuric sulfate (HgSO₄) in the presence of dilute sulfuric acid (H₂SO₄) and water.

6. Nucleophilic Substitution (Gattermann-Koch Reaction)

• Aldehydes:

  • Aldehydes can be synthesized from haloalkanes via the Gattermann-Koch reaction, which involves the reaction with hydrogen cyanide (HCN) and a Lewis acid catalyst like anhydrous aluminum chloride (AlCl₃), followed by hydrolysis.

7. Grignard Reagents

• Ketones:

  • Ketones can be produced by reacting Grignard reagents (RMgX) with nitriles, followed by hydrolysis of the resulting imine.

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