F324 Unit 4: Carbonyl compounds: Aldehydes, Ketones, Carboxylic Acids, Esters and Triglycerides

  • Created by: Saoirse
  • Created on: 07-06-14 22:13

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

Nucleophilic addition:

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

Carboxylic acids

Very soluble…


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