Formula sheet: Aldehydes, Ketones and Carboxylic Acids
Aldehydes, Ketones and Carboxylic Acids14 min readLesson 1 of 6
1.1 Named reactions and conditions
| Reaction | Reagents and conditions | Product |
|---|---|---|
| Rosenmund reduction | Acid chloride, H2 over Pd on BaSO4 poisoned with quinoline | Aldehyde |
| Oxidation of a primary alcohol | PCC, or CrO3 in anhydrous medium | Aldehyde |
| Dehydrogenation | Alcohol vapour over hot copper at 573 K | Aldehyde or ketone |
| Hydration of an alkyne | Ethyne with dilute H2SO4 and HgSO4 | Acetaldehyde |
| Ozonolysis | Alkene with O3 at 195 K, then zinc and water | Aldehyde or ketone |
| Nucleophilic addition | HCN, NaHSO3, or Grignard then hydrolysis | Cyanohydrin, bisulphite adduct, alcohol |
| Acetal formation | Aldehyde with an alcohol and dry HCl | Acetal |
| Aldol condensation | Carbonyl compound with dilute NaOH, then heat | Alpha, beta unsaturated carbonyl |
| Cannizzaro reaction | Aldehyde with no alpha hydrogen and concentrated NaOH | Alcohol plus carboxylate |
| Clemmensen reduction | Zinc amalgam with concentrated HCl | CH2 from C=O |
| Wolff Kishner reduction | Hydrazine, KOH, ethylene glycol, heat | CH2 from C=O |
| Tollens test | Ammoniacal silver nitrate, warm | Silver mirror with aldehydes |
| Fehling test | Fehling A and B, warm | Red precipitate with aliphatic aldehydes |
| Iodoform test | Iodine with NaOH, warm | Yellow precipitate with methyl ketones |
| HVZ reaction | Carboxylic acid, red phosphorus, halogen | Alpha halo acid |
| Decarboxylation | Sodium salt with soda lime, heat | Alkane with one carbon less |
1.2 Structure and reactivity
The carbonyl carbon is sp2 hybridised and planar, with bond angles near 120 degrees. The carbon oxygen bond is polar, so the carbonyl carbon carries partial positive charge and nucleophiles attack it. Aldehydes react faster than ketones: the carbonyl carbon is less crowded, and a ketone has two alkyl groups releasing electron density through the inductive effect while an aldehyde has only one.
1.3 Acidity numbers
Carboxylic acids are much stronger acids than alcohols or phenols. Ethanoic acid has pKa 4.76. Chlorine raises the acidity, so chloroethanoic acid has pKa 2.86, dichloroethanoic acid 1.48 and trichloroethanoic acid 0.64. Alkyl groups lower acidity, so methanoic acid is stronger than ethanoic acid, which is stronger than propanoic acid.