1 Distillation and reflux / PAG5

Organic techniques Distillation In general used as separation technique to separate an organic product from its reacting mixture. Need to collect the distillate of the approximate boiling point range of the desired liquid. Classic AS reaction using distillation Reaction: primary alcohol
aldehyde Reagent: potassium dichromate (VI) solution and dilute sulphuric acid. Conditions: use a limited amount of dichromate and warm gently and distil out the aldehyde as it forms [This prevents further oxidation to the carboxylic acid] CH3CH2CH2OH + [O]
CH3CH2CHO + H2O Observation Orange dichromate solution changes to green colour of Cr3+ ions Reflux Classic AS reaction using reflux Reaction: primary alcohol
carboxylic acid Reagent: potassium dichromate(VI) solution and dilute sulphuric acid Conditions: use an excess of dichromate, and heat under reflux: (distill off product after the reaction has finished using distillation set up) CH3CH2CH2OH + 2[O]
CH3CH2CO2H + H2O Observation Orange dichromate solution changes to green colour of Cr3+ ions Reflux is used when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids. Never seal the end of the condenser as the build up of gas pressure could cause the apparatus to explode. This is true of any apparatus where volatile liquids are heated Water in Water out Liebig condenser thermometer Heat Anti-bumping granules are added to the flask in both distillation and reflux to prevent vigorous, uneven boiling.