oxidation of alcohols

• What makes an alcohol primary?

  the C atom bonded to the OH is only bonded to one other C atom
• What makes an alcohol secondary?

  the C atom bonded to the OH is bonded to two other C atoms
• What makes an alcohol tertiary?

  the C atom bonded to the OH is bonded to 3 other carbon atoms
• What forms if you partially oxidise a primary alcohol?

  an aldehyde
• What conditions are needed to partially oxidise a primary alcohol?

  H2SO4

  potassium dichromate (VI)

  distill product as it's produced

  gentle heating
• What is an equation of for the partial oxidation of ethanol?

  CH3CH2OH (l) + [O] -> CH3CHO + H2O (l)
• What forms if you fully oxidise a primary alcohol?


  a carboxylic acid
• What conditions are needed to fully oxidise a primary alcohol?

  concentrated H2SO4

  potassium dichromate

  reflux

  strong heating
• What is the equation for the full oxidation of ethanol?


  CH3CH2OH (l) + 2[O] -> CH3COOH (g) + H2O (l)
• What forms if you oxidise a secondary alcohol?

  a ketone
• What conditions are needed for the oxidation of a secondary alcohol?

  concentrated H2SO4

  potassium dichromate (VI)

  strong heating
• What is the equation for the oxidation of propan-2-ol?

  CH3CH(OH)CH3 (l) + [O] -> CH3COCH3 (g) + H2O (l)
• Is it possible to oxidise a tertiary alcohol?

  no
• What is the oxidising agent used to prepare aldehydes and ketones from alcohols?

  acidified potassium dichromate (K2Cr2O7)

  • acidified potassium dichromate(VI), K2Cr2O7, is an orange oxidising agent
  • When the alcohols are oxidised the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions
• How are aldehydes formed?

  • a primary alcohol is added to the oxidising agent and warmed
  • The aldehyde product has a lower boiling point than the alcohol reactant so it can be distilled off as soon as it forms
  • If the aldehyde is not distilled off, further refluxing with excess oxidising agent will oxidise it to a carboxylic acid 
• what happens to primary alcohols when they're oxidised?

  when primary alcohols are heated in the presence of acidified potassium dichromate (VI) they're oxidised to aldehydes
• What happens to an aldehyde when they're heated further with acidified potassium dichromate?

  the aldehyde is oxidised to produce carboxylic acids

  this shows primary alcohols are oxidised to aldehydes and then to carboxylic acid
• What happens when acidified potassium dichromate ions are oxidised?


  they will turn from orange to green as they are reduced to Cr3+ ions

  this can be used as a way to distinguish between primary/secondary alcohols and tertiary alcohols (tertiary alcohols don't oxidise so will remain orange)
• What is reflux?

  the continual boiling and condensing of a reaction mixture to ensure the reaction goes to completion without the mixture billing dry
• What is distillation?

  the process of separating a mixture due to the difference in boiling points
• oxidation of primary alcohol to aldehyde?


  it's essential to distil off the aldehyde before it gets oxidised to a carboxylic acid

  the alcohol is dripped into a warm solution of acidified K2Cr2O7

  the aldehyde has a low boiling point (no hydrogen bonding) - it distils off

  if it didn't distil off it would be oxidised to the equivalent carboxylic acid

  to oxidise an alcohol straight to a carboxylic acid you'd reflux the mixture