Oxidation of Alcohols

Question 1

How and what can primary alcohols be oxidised to? Give an example

Answer 1

Aldehydes
Heated in the presence of acidified potassium dichromate and then distilled
Ethanol + [O] -> Ethanal + water

Question 2

How and what can primary alcohols be further oxidised to? Give an example

Answer 2

Carboxylic acids
Heated further under reflux conditions

Ethanal + [O] -> Ethanoic acid + water

Question 3

How and what can secondary alcohols be oxidised to? Give an example

Answer 3

Ketones
Heated under reflux in the presence of acidified potassium dichromate

Propan-2-ol + [O] -> propanone + water

Question 4

What can tertiary alcohols be oxidised to

Answer 4

They are not easily oxidised

Question 5

How is potassium dichromate acidified?

Answer 5

With dilute sulfuric acid

Question 6

How do you distinguish between aldehydes and ketones?

Answer 6

Tollens’ Reagent or Fehling’s Solution

Question 7

Describe the use of Tollens’ Reagent

Answer 7

Heat gently
Only aldehydes are oxidised into a carboxylic acid. The silver(I) ions are reduced to silver atoms. This is seen by a silver mirror coating the inside of the test tube.
Ketones result in no visible change.

Question 8

Describe the use of Fehling’s Solution

Answer 8

Heat gentle
Only aldehydes are oxidised into a carboxylic acid. The copper(II) ions are reduced to copper(I) oxide. This is seen by the blue Cu+2 ions in the Fehling’s Solution change to a red precipitate of Cu2O.
Ketones do not react.

Question 9

How do you test the presence of a carboxylic acid?

Answer 9

Add sodium carbonate. It will fizz and produce carbon dioxide.