CPAC 7 - Oxidation of propan-1-ol to produce propanal and propanoic acid

Testing for propanoic acid

- Adding tollen's reagent will not result in the formation of a silver mirror - Effervescense produced when magnesium ribbon is added - Effervescence produced when adding sodium hydrogencarbonate - Adding Fehling's solution will not result in colour change from blue

Testing for propanal

- Adding tollen's reagent will result in the formation of a silver mirror - No effervescense produced when magnesium ribbon is added - No effervescence produced when adding sodium hydrogencarbonate - Adding Fehling's solution will result in a reddish-brown colour change from blue

Why does the test tube for collecting the distillate need to be surrounded by cold water?

- Propanal has a low boiling point, so collecting it at a low temperature prevents it from immediately evaporating.

What happens when secondary and tertiary alcohols are oxidized?

- Secondary alcohols are oxidised to ketones. E.g. oxidising propan-2-ol forms propanone. - unlike in the oxidation of primary alcohols, there is no lone hydrogen bonded to the carbon atom which has a double-bonded oxygen (the aldehyde group). So it is not possible for any further oxygen to be added to produce a carboxylic acid. - Tertiary alcohols are not easily oxidised because unlike primary and secondary alcohols, they do not have a hydrogen atom attached to the same carbon atom as the hydroxyl (OH) group.

Equation of the oxidation of propan-1-ol to propanoic acid

CH3CH2CH2OH + 2[O] = CH3CH2COOH + H2O

Equation of the. oxidation of propan-1-ol to propanal

CH3CH2CH2OH + [O] = CH3CH2CHO + H2O

Why should water enter the condenser from the bottom?

Feeding water in from the bottom of the condenser ensures that the entire condenser is filled with water. this produces efficient cooling.

Why can propanal only be obtained without the reflux step?

Heating the mixture under reflux means that the propanal produced is constantly returned to the reaction vessel, so it is further oxidised to propanoic acid

What is meant by the term 'reflux'?

Heating under reflux involves boiling a reaction mixture, cooling the vapours in a condenser and returning them to the mixture. It is a simple and effective way of maintaining a constant reaction temperature. As organic reactions can be very low, it ensured that the reaction takes place without the reaction flask boiling dry.

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

They are added to promote smooth, even boiling. The granules help prevent large bubbles from forming in the reaction mixture when it is heated.

Why does the propan-1-ol should be added slowly to the acidified potassium dichromate (VI)?

This prevents any dangerous splashing as the reaction is exothermic