Oxidation: propan-1-ol to produce propanal & propanoic acid

• Oxidation of propan-1-ol to produce propanal

  1. Wear protective gloves

  2. Add acidified potassium dichromate solution to flask

  3. Set up flask for distillation

  4. Add anti-bumping granules

  5. Add propan-1-ol solution slowly

  6. Heat gently

  7. Collect distillate
• Oxidation of propan-1-ol to produce propanoic acid

  1. Wear protective gloves

  2. Add acidified potassium dichromate solution to flask

  3. Set up flask for reflux

  4. Add anti-bumping granules

  5. Add propan-1-ol solution slowly

  6. Heat gently under reflux

  7. Distil product
• Refluxing


  • Technique used in chemistry where the vapour from a reaction is condensed and returned to the reaction vessel
• Refluxing


  Allows reactions to be carried out at the boiling point of the solvent for an extended period of time
• Anti-bumping granules are added to the reaction mixture
• Water should enter the condenser at the bottom
• The distillate needs to be collected in a test tube surrounded by cold water
• Testing for propanal

  1. Silver mirror test

  2. Magnesium ribbon test

  3. Sodium hydrogencarbonate test

  4. Fehling's solution test

  
• Testing for propanoic acid

  1. Silver mirror test

  2. Magnesium ribbon test

  3. Sodium hydrogencarbonate test

  4. Fehling's solution test

  
• Oxidation of propan-1-ol to propanal

  CH3CH2CH2OH + [O] → CH3CH2CHO + H2O
• Oxidation of propan-1-ol to propanoic acid

  CH3CH2CH2OH + 2[O] → CH3CH2COOH + 2H2O
• Propanal can only be obtained without the refluxing set up
• Propan-1-ol is a primary alcohol
• Testing for propanal (silver mirror test)

  Prepare a sample of Tollens’ reagent by adding 5 drops of sodium hydroxide

  solution to 2 cm3 of silver nitrate solution in a test tube.

  2. Add just enough dilute ammonia solution to this test tube so that the brown

  precipitate dissolves completely. Using a water bath, gently warm this test tube.

  3. Add 10 drops of the distillate obtained in step 8. If propanal has been produced, a

  silver mirror will appear on the walls of the test tube.
• Testing for propanal (magnesium ribbon)


  Add a small piece (1 cm length) of magnesium ribbon to the distillate.

  2. Observe any reaction. Propanal does not react with magnesium, so nothing

  should be seen happening in the test tube.
• Testing for propanol (sodium hydrogencarbonate)

  Add a spatula of sodium hydrogencarbonate to the distillate in a test tube.

  2. Observe any reaction. Propanal does not produce any effervescence.
• Testing for propanal (Fehling's solution)

  Add 1 cm3 Fehling’s solution to 1 cm3 of the distillate in a test tube.

  2. Place the test tube into a beaker of hot water. A colour change to reddish-brown

  indicates propanal is present.
• Testing for propanoic acid (silver mirror test)

  Prepare a sample of Tollens’ reagent by adding 5 drops of sodium hydroxide

  solution to 2 cm3 of silver nitrate solution in a test tube.

  2. Add just enough dilute ammonia solution to this test tube so that the brown

  precipitate dissolves completely. Using a water bath, gently warm this test tube.

  3. Add 10 drops of the distillate obtained in step 8. If propanoic acid has been

  produced a silver mirror will not appear on the walls of the test tube.
• testing for propanoic acid (magnesium)


  Add a small piece (1 cm length) of magnesium ribbon to the distillate.

  2. Observe any reaction. Propanoic acid does react with magnesium, so some effervescence should be seen in the test tube.
• Testing for propanoic acid (sodium hydrogen carbonate)

  Add a spatula of sodium hydrogencarbonate to the distillate in a test tube.

  2. Observe any reaction. Propanoic acid does produce effervescence and this

  should be clearly seen.
• Testing for propanoic acid (fehling's solution)

  Add 1 cm3 Fehling’s solution to 1 cm3 of the distillate in a test tube.

  2. Place the test tube into a beaker of hot water. Propanoic acid does not cause

  Fehling’s solution to change colour.
• What is meant by the term ‘refluxing’?


  Refluxing is a simple and effective way of maintaining a constant reaction temperature.
• Why do some experiments require refluxing?

  Organic reactions can be very slow, refluxing ensures that the reaction takes place without

  the reaction flask boiling dry.
• In step 5 in both experiments, why do you have to add the propan-1-ol solution

  slowly?


  Adding propan-1-ol solution slowly prevents any dangerous splashing as the reaction is

  exothermic.
• Why are anti-bumping granules added to the reaction mixture?

  Anti-bumping granules are added to promote smooth, even boiling. The granules help prevent

  large bubbles forming in the reaction mixture when it is heated.
• Why should the water enter the condenser at the bottom?

  Water entering from the bottom of the condenser ensures that the entire condenser is filled with

  water. This produces efficient cooling.
• Why do you need to collect the distillate in a test tube which is surrounded by cold

  beaker?

  Propanal has a low boiling point, so collecting it at a low temperature prevents the distillate

  immediately evaporating.
• Why can propanal only be obtained without the refluxing set up?

  Refluxing causes the propanal produced to be further oxidised to propanoic acid as it is

  constantly returned to the reaction vessel.