Unit 4 - Laboratory Techniques and their Application
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Unit 4 Aim C: Preparation and Testing of Aspirin/Acetylsalicylic Acid (DISTINCTION)
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Unit 4 - Laboratory Techniques and their Application
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PEARSON (PEARSON)
This is my distinction grade assignment for unit 4 aim C on the preparation and testing of aspirin/acetylsalicylic acid, including the industrial manufacture. All criteria were met and I was awarded distinction.
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Unit 4 - Laboratory Techniques and their Application
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Laboratory and Industrial Production of Aspirin
Aspirin, also known as Acetylsalicylic Acid, is a white, odourless crystal or crystalline powder which is
a non-steroidal anti-inflammatory drug (NSAID) to treat pain, fever, inflammation and to thin the
blood. It was first synthesised in 1899 by Felix Hoffman at Bayer Pharmaceuticals by reacting an
acetic group with salicylic acid. Previously, plants such as willow bark which contain salicilin had
been used to treat pain and fever as salicilin is a precursor to salicylic acid, a component of aspirin.
Today, it is synthesised in an esterification reaction between salicylic acid and acetic anhydride.
During the reaction, acetic anhydride converts salicylic acid’s hydroxyl group, R-OH, into an ester
group, R-OCOCH₃, this reaction also produces acetic acid as a by-product - a concentrated sulfuric
acid catalyst is usually used to increase the yield of the reaction. The equation for this reaction can
be seen in figure 1 below. This practical utilises two main techniques: vacuum filtration and
recrystallisation. Vacuum filtration involves using a Buchner flask to increase the rate of filtration by
utilising a pressure gradient rather than the force of gravity alone. This technique allows a variable
rate of filtration and is more effective than filtering alone (3). Recrystallisation is a technique used to
purify crystal products, by dissolving it in a heated solution, then allowing it to cool and form crystals
again, while impurities remain in the solution and can be filtered out.
Figure 1: Symbol Equation for Producing Aspirin (1)
• Salicylic acid – can cause serious eye damage, wear goggles. Harmful if swallowed, do not
ingest.
• Acetic anhydride – highly corrosive, do not allow contact with eyes or skin. Can cause
respiratory irritation.
• Sulphuric acid – extremely corrosive, do not allow contact with skin or eyes. Can cause
serious respiratory irritation, use only in a fume hood.
, Method:
Step 1: The first step in this practical is boiling the reagents together using a water bath. 5.002g
salicylic acid, 7ml acetic anhydride and 8 drops of concentrated sulphuric acid were measured into a
600ml beaker and placed in a water bath and allowed the water to boil – then heated the mixture
for a further 15 minutes. The sulphuric acid could not be removed from the fume hood and the
mixture only removed when ready to be used, to avoid inhaling the dangerous fumes. During this,
the esterification reaction between the acetic anhydride and salicylic acid took place, using sulphuric
acid as a catalyst.
Figure 2: Acetic Anhydride. Figure 3: Reagent Mixture. Figure 4: Heating in Water Bath.
Step 2: Next, the flask was allowed to cool and moved to an ice bath in the fume cupboard where
5ml of ice water was added to facilitate the decomposition of excess acetic anhydride. Another 15ml
of ice water was then added and the mixture swirled. It was left to cool for around 15 minutes while
the mixture crystalized, the inside of the flask was scratched with a glass rod to allow the crystals to
develop more easily. Once formed, the crystals were collected in a Buchner funnel with a filter
paper, which was seated with a small amount of water. The flask with the product was rinsed out
with 3ml ice water to remove any remaining crystals, it must be ice cold to prevent the crystals from
dissolving and only a small amount used to prevent losing too much of the product.
Figure 5: Crystallization in Ice Bath. Figure 6: Crystals in Buchner Funnel
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