This chemical can be converted by the body after it is eaten into another chemical, salicylic acid. salicylic acid (made from salicin), and close relatives were used at high doses to treat pain and swelling in diseases like arthritis and to treat fever in illnesses like influenza (flu). Felix Hoffmann was another scientist who reasoned that salicylic acid may be irritating because it is an acid, he put the compound through a couple of chemical reactions that covered up one of the acidic parts with an acetyl group, converting it to acetylsalicylic acid (ASA). He found that ASA not only could reduce fever and relieve pain and swelling, but he believed it was better for the stomach and worked even better than salicylic acid.
Aspirin is usually prepared by reacting salicylic acid with acetic anhydride in the presence of concentrated sulfuric acid as a catalyst. This reaction is known as an Ester Formation reaction.
Hypothesis to be tested (Objective)
Does the Aspirin produced in the laboratory have a different melting point and yield compared to that of Aspirin manufactured on a Commercial and Industrial scale?
The hypothesis is to produce aspirin in the laboratory by subsequent in a simple set of instructions the melting point and yield of the product will be obtained. This shall be judged against to the melting and yield of aspirin achieved from the industrial specification and manufacture of the product.
Experimental Plan:
Before beginning any of the experiments it is critical that you read the COSHHE analysis sheets for each of the chemicals that are going to be used in the experiments. This is to minimise the chance of chemical accidents that can occur during the experiment.
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- Measure and weigh 50grams of Salicylic acid on the measuring scale
- Measure and collect 80ml of Acetic anhydride
- Mix 50g Salicylic acid with 80ml of acetic anhydride in a suitable round-bottomed Quick-fit flask.
- In both of the mixtures of Salicylic acid and acetic anhydride add some concentrated Sulphuric acid but not more than 0.5 ml
- After mixing the chemicals together you are now required to carry out the main stage of the experiment. Firstly make sure that the Quick-fit flask is sealed safely together, or else apply a small amount of medium oil for better sealant.
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Heat the solution gently for 30 minutes at not more than 700C.
- During the heating process it is essential to start mixing the mixtures inside the round-bottomed Quick-fit flask, as this can be achieved when the temperature has reached 70˚C, turn of the heating element and let mixture cool down to 50˚C and pour 750ml contents of cool water.
- After adding water to the contents of the mixed solution, you are then required to filter the product by using the filter paper and a vacuumed container for improved filtration and to dry the product.
- Weigh the product again and record the differences.
- Calculate the yield of the product.
- Measure the melting point of the substance by using the pipette and the apparatus required for the melting point. And record the melting point takes place.
Method
A sample of mass 50g of salicylic acid was weighed out on a watch glass and then transferred to a 100cm3 three neck round bottomed flask. The flask was clamped over a heating mantle and the thermometer was fitted into one of the necks of the flaks this was done using a thermometer adaptor. The height of the bulb was adjusted so that it was near the bottom of the flask then was able to be immersed in the reaction mixture.
A condenser was fitted into one of the other necks of the flask and third outlet of the flask was stoppered. Then the of acetic anhydride was added to the salicylic acid and not more than 0.5 ml concentrated sulphuric acid were added to mixture using Pasteur pipette. The flask was heated to 700C for 30 minutes. It was ensured that the reagents in the flaks were allowed to cool to 500C and the contents of the reaction mixture were poured into 750ml cold water. The precipitate formed, which was collected by suction filtration. Product was washed on the filter paper using tow sets 10cm3 of cold water and then product was allowed to dry on the filter paper for 10 minutes under suction. The mass of the damp product was weighed, and recrystallised using the minimum amount of hot water. The recrystallised product was collected by suction filtration. The crystals were washed in situ using tow sets of 10cm3 of cold water. The crystals were let to dry for a week and the mass was recorded. This value was used to calculate the percentage yield of the acetylation reaction.
Hazard and Risk Analysis
COSHHE Analysis for the chemicals Look at Appendices
With all experiments the main precautions that are taken are head, eye and clothes protection. Gloves were also worn to protect the hands when handling equipment. Extra precaution was taken when pouring the product into the mould due to the hazardous and corrosive properties of the reactants.
Lab coats, Goggles and Gloves
Apparatus
3- Neck flask
Beaker
Ring stand and clamp
Round bottom quick fit glass
Thermometer
Watch glass
Micro pipette
Heater element apparatus
Plastic beakers
Data
Mass of aspirin = 215.0400g
Melting of aspirin 114.30C
Melting of aspirin 116.40C
Melting point published 1350C -1400C
Mass of watch glass = 185.5367g
Dried Aspirin = 209.176
Results
When water was added to the beaker a gradual colour change was observed from colourless to brown.
Following washing the yield was recorded on the balance and found to be 36.19%.
The crystals appeared to be pure white in colour at this stage.
Calculations
1 mole salicylic acid 138g
1 mole of Aspirin = 180g
138g of salicylic acid
180g Aspirin there for 50g of salicylic acid will react to give theoretical yield
50 x 180
---------- = 65, 21 = Theoretical yield.
138
To calculate the percentage yield formula used = mass obtained divided mass expected x 100
Mass obtained / mass expected x 100 = yield %
185.5367 – 209.1765 = mass obtained
23.60
------ X 100 = 36.19
65.21
Discussion and interpretation:
The experiment worked, in that pure white crystals were obtained and Aspirin in its pure form is a white crystalline solid. The yield obtained 23.60g. It is never possible in any experiment to get a perfect 100% yield. This is due to factors, such as the reagents used are not themselves totally pure and also that, due to kinetic theory of chemical reactions, all of the reagents will never fully react. In addition the esterification process is an equilibrium reaction, and there a 100% yield is never possible en under ideal conditions. In order to calculate the maximum possible yield, the value Kc the equilibrium constant, under these conditions would be required kc is the ratio of products to reactants at equilibrium. This reason is why; often one reagent is added in excess. This uses Le Chataliers principle, which in effect means that when one of the reactants is in excess, the equilibrium will be shifted more favourable towards the products. Also there will be inevitable errors in mass readings from the balance, losses on transferring materials and losses on filtration and
washing. These later losses are always a compromise in that the more it is washed the purer it will be, but the more that will be lost. Overall the percentage yield of 36.19 is fairly good for a first time attempt at the experiment.
Apendix E
P1 PREPARATION OF ASPIRIN
Preparation
Write a balanced equation for the synthesis of aspirin from salicylic acid and acetic anhydride?
What is the correct chemical name for aspirin?
Acetylsalicylic
From the handbook of chemistry and physics find out the melting point of aspirin.
1350C -1400C
What is the solubility of aspirin in water?
0.05
How is this affected by temp changes?
Cool temp causes aspirin to catalyse.
What are the major differences between your experimental process and the process not widely used in industry?
