Carbonyl compounds are those that contain the functional group C=O
Aldehydes and ketones
In aldehydes the carbonyl group is found at the end of the chain and the suffix is '-al'
In ketones the carbonyl group is mid chain and the suffix is '-one'
Oxidation of alcohols and aldehydes
Use oxidising agent H+/(CR2O7)2- and conc H2SO4 catalyst
Primary alcohols are oxidised into aldehydes via distillation and carboxylic acids via reflux.
Ethanol to ethanal: CH3CH2OH +[O] -> CH3CHO + H2O (distil)
Ethanol to ethanoic acid: CH3CH2OH + 2[O] -> CH3COOH +H2O
Secondary alcohols are oxidised into ketones using distillation or reflux.
Propan-2-ol to propanone: CH3CHOCH3 + [O] -> CH3COCH3 +H2O
Use NaBH4 as a source of hydride ions, :H-, which act as the nucleophile
- e- deficient C in polar C=O bond is attacked by :H-
- Lone pair of e-s from :H- forms a bond with C atom
- pi bond in C=O breaks to produce negatively charged intermediate
- Intermediate donates an e- pair to a H atom of a H2O molecule, formaing a dative covalent bond and a hydroxide ion
- Organic addition product is an alcohol
Chemical tests for carbonyl compounds
- To detect the presence of a carbonyl group:
- Use 2,4-DNP (Brady's reagent)
- Orange precipitate forms if aldehyde or ketone is present
- To identify whether an aldehyde or ketone:
- Use Ammoniacal silver nitrate (Tollen's reagent)
- Silver mirror forms if aldehyde is present, no reaction if ketone