Chapter 8 · Chemistry
Making Aldehydes and Ketones: Methods and Named Reactions
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Four routes make both aldehydes and ketones (from alcohols, alkenes and alkynes); named reactions make only one: Rosenmund, Stephen, Etard and Gatterman-Koch for aldehydes; Grignard on nitriles, dialkylcadmium and Friedel-Crafts acylation for ketones.
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Same Weight, 0 °C vs 97 °C: Physical Properties of Aldehydes and KetonesFive compounds of the same mass boil from 0 °C to 97 °C. Aldehydes and ketones sit in the middle: their polar C=O gives dipole-dipole attraction, but with no O–H they cannot hydrogen-bond with each other. Water can hydrogen-bond to the C=O oxygen, so small aldehydes and ketones mix with water while long chains do not.Chemistry
Key points
- Both: oxidation or Cu/Ag dehydrogenation of alcohols (1° → aldehyde, 2° → ketone), ozonolysis of alkenes, hydration of alkynes (ethyne → ethanal).
- Rosenmund: RCOCl + H₂, Pd–BaSO₄ → RCHO. Stephen: RCN + SnCl₂/HCl → imine → RCHO.
- Etard: toluene + CrO₂Cl₂ → benzaldehyde. Gatterman-Koch: benzene + CO + HCl, anhyd. AlCl₃ → benzaldehyde.
- Ketones: RCN + R′MgX then H₃O⁺; RCOCl + R′₂Cd; Friedel-Crafts acylation of benzene (RCOCl, anhyd. AlCl₃).
Routes for both
| From | Reagent | Gives |
|---|---|---|
| 1° / 2° alcohol | oxidation, or Cu/Ag + heat | aldehyde / ketone |
| alkene | O₃, then Zn/H₂O | aldehydes and/or ketones |
| alkyne | H₂O, HgSO₄, dil. H₂SO₄ | ethanal from ethyne; others ketones |
Named reactions
| Reaction | Gives | Reagents |
|---|---|---|
| Rosenmund reduction | aldehyde | RCOCl, H₂, Pd–BaSO₄ |
| Stephen reaction | aldehyde | RCN, SnCl₂/HCl, then H₃O⁺ |
| Etard reaction | benzaldehyde | toluene, CrO₂Cl₂, then H₃O⁺ |
| Gatterman-Koch | benzaldehyde | benzene, CO + HCl, anhyd. AlCl₃ |
| Grignard + nitrile | ketone | RCN, R′MgX, then H₃O⁺ |
| Dialkylcadmium | ketone | RCOCl, R′₂Cd |
| Friedel-Crafts acylation | aryl ketone | benzene, RCOCl, anhyd. AlCl₃ |
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