Unit 4: Aspirin Synthesis
Synthesis and Purification of Aspirin
The aim of this part is to synthesise and purify aspirin.
Synthesis of Crude Aspirin
5.0g of 2-hydroxybenzoic acid (salicylic acid) was weighed into a 100cm3 conical flask, and
7cm3 of ethanoic anhydride was also carefully added. Plastic gloves were always worn when
handling ethanoic anhydride. Then, 2 to 3 drops of concentrated sulphuric acid were added.
The contents of the flask were thoroughly swirled to ensure the proper mixing; the flask was
heated on a water bath at 50 to 60°C for 15 to 20 minutes, whilst swirling it occasionally. The
flask was then left to cool and 75cm3 of distilled water was added. The contents of the flask
were then stirred well and filtered under reduced pressure.
Purification of the Crude Product
The filtered solid was placed into a 250cm3 beaker and 5cm3 of ethanol was added, along with
40cm3 of distilled water. The beaker was heated gently until all the aspirin had been dissolved.
It was ensured that the solution was not boiled, as this would have degraded the aspirin. Since
the did not all dissolve despite it having reached the boiling stage, more ethanol was added,
1cm3 at a time, until it had all dissolved. The solution was then slowly left to cool; this is when
needle-like crystals of aspirin started forming. A decent amount of crystals had formed; this is
when it was left to thoroughly cool down, using an iced water bath and it was filtered under
reduced pressure. The crystals were washed with some cold distilled water and was left to dry.
Results
Mass of Watch Glass 35.86g
Mass of Damp Crude Aspirin 9.33g
Mass of Dry Crude Aspirin 7.46g
Mass of Damp Pure Aspirin 4.55g
Mass of Dry Pure Aspirin 3.61g
% Yield Calculation
Mass 2-hydroxyybenzoic acid = 5.0g The reaction can produce moles of aspirin
by a 100% reaction
Mr 2-hydroxybenzoic acid = 138.12g What would this mass be?
n° moles = 𝒎𝒂𝒔𝒔⁄𝑴𝒓 = 𝟓⁄𝟏𝟑𝟖. 𝟏𝟐 Mass = moles × Mr = 0.036 × 180.16
, 5.0g 2-hydroxybenzoic acid = 0.036 moles Theoretical 100% yield mass = 6.49g
Conclusion
Crude aspirin
6.46
% yield crude aspirin (dry) = 6.49 × 100 = 115% yield
9.33
% yield crude aspirin (damp) = 6.49 × 100 = 144% yield
Recrystallised aspirin
3.61
% yield pure aspirin (dry) = 6.49 × 100 = 55% yield
4.55
% yield pure aspirin (damp) = 6.49 × 100 = 70% yield
Mass
The mass of dry crude aspirin is 9.33g.
The mass of damp crude aspirin is 7.46g.
The mass of damp pure aspirin is 4.55g.
The mass of dry pure aspirin is 3.61g.
Evaluation
Yield (amount produced)
In the pharmaceutical industry, it is necessary for them to utilize pharma chemical reagents
that are 99.95% pure. This level of purity is pricey. At college, General Purpose Reagents (GPR)
are priced roughly a quarter of their cost, and it is 96% pure. This means if all the salicylic acid
turns into aspirin, your yield will already be 4%.
When the aspirin formed in the conical flask, and had to be transferred to the filter, some was
left behind. Attempts were made to scrape and wash this out, but some is always left behind.
Aspirin crystals may be lost between the filter paper's fibres during filtering. When scraping
the aspirin out of the filter, some of it was left behind as it is impossible to recover it all. When
we recrystalised the aspirin, even cooling in ice to maximise crystallisation, there would be
some aspirin dissolved in the cold solution which will pass through the filter. More was lost
when scraping out of the filter, both on the funnel and the spatula.
Purity of our Final Aspirin
In the pharmaceutical industry, they are required to use the pharma chemical reagents that
are 99.95% pure, this level of purity is pricey. At college, we use General Purpose Reagents
Synthesis and Purification of Aspirin
The aim of this part is to synthesise and purify aspirin.
Synthesis of Crude Aspirin
5.0g of 2-hydroxybenzoic acid (salicylic acid) was weighed into a 100cm3 conical flask, and
7cm3 of ethanoic anhydride was also carefully added. Plastic gloves were always worn when
handling ethanoic anhydride. Then, 2 to 3 drops of concentrated sulphuric acid were added.
The contents of the flask were thoroughly swirled to ensure the proper mixing; the flask was
heated on a water bath at 50 to 60°C for 15 to 20 minutes, whilst swirling it occasionally. The
flask was then left to cool and 75cm3 of distilled water was added. The contents of the flask
were then stirred well and filtered under reduced pressure.
Purification of the Crude Product
The filtered solid was placed into a 250cm3 beaker and 5cm3 of ethanol was added, along with
40cm3 of distilled water. The beaker was heated gently until all the aspirin had been dissolved.
It was ensured that the solution was not boiled, as this would have degraded the aspirin. Since
the did not all dissolve despite it having reached the boiling stage, more ethanol was added,
1cm3 at a time, until it had all dissolved. The solution was then slowly left to cool; this is when
needle-like crystals of aspirin started forming. A decent amount of crystals had formed; this is
when it was left to thoroughly cool down, using an iced water bath and it was filtered under
reduced pressure. The crystals were washed with some cold distilled water and was left to dry.
Results
Mass of Watch Glass 35.86g
Mass of Damp Crude Aspirin 9.33g
Mass of Dry Crude Aspirin 7.46g
Mass of Damp Pure Aspirin 4.55g
Mass of Dry Pure Aspirin 3.61g
% Yield Calculation
Mass 2-hydroxyybenzoic acid = 5.0g The reaction can produce moles of aspirin
by a 100% reaction
Mr 2-hydroxybenzoic acid = 138.12g What would this mass be?
n° moles = 𝒎𝒂𝒔𝒔⁄𝑴𝒓 = 𝟓⁄𝟏𝟑𝟖. 𝟏𝟐 Mass = moles × Mr = 0.036 × 180.16
, 5.0g 2-hydroxybenzoic acid = 0.036 moles Theoretical 100% yield mass = 6.49g
Conclusion
Crude aspirin
6.46
% yield crude aspirin (dry) = 6.49 × 100 = 115% yield
9.33
% yield crude aspirin (damp) = 6.49 × 100 = 144% yield
Recrystallised aspirin
3.61
% yield pure aspirin (dry) = 6.49 × 100 = 55% yield
4.55
% yield pure aspirin (damp) = 6.49 × 100 = 70% yield
Mass
The mass of dry crude aspirin is 9.33g.
The mass of damp crude aspirin is 7.46g.
The mass of damp pure aspirin is 4.55g.
The mass of dry pure aspirin is 3.61g.
Evaluation
Yield (amount produced)
In the pharmaceutical industry, it is necessary for them to utilize pharma chemical reagents
that are 99.95% pure. This level of purity is pricey. At college, General Purpose Reagents (GPR)
are priced roughly a quarter of their cost, and it is 96% pure. This means if all the salicylic acid
turns into aspirin, your yield will already be 4%.
When the aspirin formed in the conical flask, and had to be transferred to the filter, some was
left behind. Attempts were made to scrape and wash this out, but some is always left behind.
Aspirin crystals may be lost between the filter paper's fibres during filtering. When scraping
the aspirin out of the filter, some of it was left behind as it is impossible to recover it all. When
we recrystalised the aspirin, even cooling in ice to maximise crystallisation, there would be
some aspirin dissolved in the cold solution which will pass through the filter. More was lost
when scraping out of the filter, both on the funnel and the spatula.
Purity of our Final Aspirin
In the pharmaceutical industry, they are required to use the pharma chemical reagents that
are 99.95% pure, this level of purity is pricey. At college, we use General Purpose Reagents
