Aldehydes and Ketones

• • aldehydes are oxidised to carboxylic acids using an oxidising agent
  • ketones can't be oxidised
• Tollen's reagent:

  • silver nitrate + NaOH + dilute ammonia
  • [Ag(NH3)2]+
• testing for aldehydes - tollen's:

  • add the carbonyl to Tollen's Reagent and place in a hot water bath
  • naked flame cant be used as aldehydes and ketones are flammable
• • tollen's reagent is reduced to silver in the presence of aldehydes
  • silver mirror forms
  • no reaction with ketones
• Fehling's solution:

  • blue solution as it contains Cu2+ ions
  • added warm to aldehydes and ketones
  • positive result: blue solution to red precipitate (Cu2O)
  • remains blue if ketone is present
• • aldehydes and ketones can be reduced to alcohols
  • uses a reducing agent e.g NaBH4 - sodium borohydride
• • aldehydes are reduced to primary alcohols
  • ketones are reduced to secondary alcohols
• • the reduction of aldehydes and ketones involves a nucleophilic addition mechanism
  • acidified KCN is used to form hydroxynitriles
  • reducing agent is used to form alcohols
• if an unsymmetrical aldehyde or ketone is reacted with KCN, a mixture of enantiomers is produced
• KCN is used over HCN because it dissociates completely to release more CN- ions
• • KCN is an irritant, so it has to be used with care and safety procedures - safety goggles, gloves, lab coat
  • reacts with moisture to form toxic HCN