aldehydes and ketones

• aldehydes

  -carbonyl functional group C=O

  -carbonyl group always situated at the end of the chain

  -naming - carbonyl carbon is always 1

  eg. methanal HCHO
• ketones

  -carbonyl functional group C=O

  -carbonyl group always situated in the middle of the chain
• preparation of aldehyde

  -primary alcohol oxidised to aldehyde + water

  -oxidising agent - K2Cr2O7 / H2SO4

  -must be set up to distil the aldehyde as it is produced
• preparation of ketone

  -secondary alcohol oxidised to ketone

  -oxidising agent K2Cr2O7 / H2SO4
• further oxidation of a primary alcohol

  -aldehydes can easily be oxidised to carboxylic acid

  -primary alc to carboxylic acid - heat under reflux - aldehyde would still be produced but would evaporate and drop back into the reaction mixture and be further oxidised

  -oxidisation agent used K2Cr2O7 with H2SO4
• further oxidisation of secondary alcohols

  -no further oxidisation will take place

  -ketones do not have a readily hydrogen atom in the same way aldehydes do
• Using tollens reagent

  -contains silver(I) complex ion

  -formed when aq ammomia is added to a solution of sliver nitrate

  -if gently warmed with tollens reagent, an aldehyde will become oxidised

  -aldehyde causes colourless silver complex to become reduced to metallic Ag

  - +ve test = silver mirror

  -ketone will give a -ve test
• using felling's solution

  -is an alkaline soln containing copper(II) ions acting as the oxidising agent

  -if aldehyde is gently warmed, it will become oxidised and a brick red ppt is formed

  -soln is blue due to copper ions

  -as aldehyde is oxidised to carb. acid the blue Cu2+ reduced to Cu+ ions - brick ppt formed

  -ketone will not be oxidised so soln will stay blue
• using acidified potassium dichromate

  -aldehyde would be oxidised - orange to green

  -no reaction with ketones
• Reduction of Carboxylic Acids

  -reduced to primary alcohol and water
• reduction of aldehyde

  -reduced to primary alcohol
• reduction of ketone

  -reduced to secondary alcohol