Reactions of Aldehydes & Ketones

Oxidation of Aldehydes

• aldehydes can be oxidized to carboxylic acids by
  • chromic acid
  • Tollen’s Reagent is made of silver ion, ammonia, and hydroxide ion
  • this reaction can also be called the silver mirror test or Tollen’s test

Example with Chromic Acid

Example with Tollen’s Reagent

Formation of Hemiacetals & Acetals with Alcohols

Formation of Hemiacetals

• aldehydes/ketones and hemiacetals exist in equilibrium when dissolved in an alcohol

• the reaction to form a hemiacetal is an example of an addition reaction

  

Formation of Acetals

• aldehydes/ketones can be formed into acetals in the presence of

  • an acid catalyst
  • excess of alcohol

• this reaction results in the loss of a water molecule

• the aldehyde/ketone actually reacts with 2 molecules of the alcohol

  

Hydrolysis of Acetals

• Hydrolysis reaction: a reaction where water breaks the bonds in a compound

• The hydrolysis of an acetal is the reverse reaction of acetal formation

• This is a reversible reaction and is controlled by the amounts of reactants used

  

Reduction of Aldehydes to Alcohols

• This reaction can be done using one of two agents

  • Sodium borohydride
  • Lithium aluminum hydride (LAH)
  • also reduces carboxylic acids, esters, and amides