This question is about the preparation and analysis of paracetamol.
Paracetamol may be prepared from phenol in three stages.
In Stage 1, phenol is nitrated using dilute nitric acid.
The nitration of benzene requires concentrated nitric acid at 55 °C with a catalyst of concentrated sulfuric acid.
Both these reactions are electrophilic substitution.
(2)
A mixture of 2-nitrophenol and 4-nitrophenol is produced in Stage 1.
They are separated by steam distillation.
The boiling temperature of 2-nitrophenol is 215 °C and that of 4-nitrophenol is 279 °C.
Explain, in terms of intermolecular forces, why 4-nitrophenol has a higher boiling temperature than 2-nitrophenol.
You may include a diagram in your answer.
(2)
State the type of reagent needed to convert 4-nitrophenol into 4-aminophenol in Stage 2.
The outline procedure for Stage 3 is:
- place 1.0 g of 4-aminophenol in a conical flask. Add 9 cm3 of distilled water and stir the mixture
- add 1 cm3 of ethanoic anhydride to the flask and shake the mixture until a precipitate of impure paracetamol forms
- remove the paracetamol by filtration under reduced pressure
- recrystallise the paracetamol using water as the solvent
- determine the melting temperature of the pure, dry paracetamol.
(3)
Describe the recrystallisation process to obtain a pure, dry sample of paracetamol.
(5)
Describe what happens to the melting temperature if the paracetamol is not pure.
(2)
The percentage by mass of paracetamol in three brands of paracetamol tablets are shown in the table.
Brand of tablet | Percentage by mass of paracetamol |
P | 92.1 |
Q | 93.6 |
R | 99.7 |
The amount of paracetamol in a tablet can be determined using a titration with cerium(IV) ions.
The tablets are crushed and then hydrolysed in acid to form 4-aminophenol.
A tablet from one of the three brands of paracetamol was analysed following the outline procedure.
- one of the tablets was crushed and 0.500 g of the powder was added to dilute sulfuric acid
- the mixture was heated under reflux until the hydrolysis was complete
- the solution was made up to 100.0 cm3 in a volumetric flask
- 25.0 cm3 portions of the solution were titrated against 0.100 mol dm−3 Ce4+ using ferroin as indicator
Result
The mean titre was 16.50 cm3
(1)
(5)
Did this page help you?