Synthesis of Aspirin
Min CheNancy HuiAmy Qu
Rosie Zhang
Overview Introduction Experiment Chemical Used Equipment Used Observation Calculation Conclusion and Analysis Suggested Modifications Sources of Error
Introduction
Medicinal properties pain reliever fever reducer swelling-reducing drug
Active ingredient - salicylic acid
Most commonly used
drugs
Introduction Medicinal properties
of acetylsalicylic acid known for millennia
1800’s – Salicylic Acid isolated
1893 – Felix Hoffmann Jr. synthesized acetylsalicylic acid
Experiment Prepare aspirin by chemical synthesis Esterification reaction
ester + acid -> more complex ester
Recrystallize to purify the product Melting point and percentage yield determine
the purity of the aspirin
Salicylic Acid
Chemical Acetic anhydride Salicylic acid (solid) Sulphuric acid Ethyl alcohol Distilled water
Acetic Anhydride
Equipment Beaker Test tubes Balance Graduated cylinder Thermometer Dropper Hot plate Scoopula Melttemp apparatus Stirring rod
Watch glass Buchner funnel Two pieces filter
paper Wash bottle Dessicator with
silica
Procedures
Synthesis of Aspirin Heat a large beaker full of water to 75-85˚C. Weigh out 3.0 g of salicylic acid and deposit
in a large test tube. Measure 6.0 mL of acetic anhydride and
deposit into the test tube as well. Add 10 drops of 85% sulphuric acid to the
test tube and stir with a stirring rod. Place the test tube in the large beaker of
water on the hot plate, stirring occasionally for about 10 minutes.
Procedures
Crystallizing the Aspirin Remove beaker from heat and add 20 drops of
cold distilled water to the test tube. Allow the mixture to cool to room temperature. Cool the mixture further by placing the test tube
in a large beaker full of ice water to crystallize. Weigh the filter paper with a watch glass and fill
a wash bottle with around 25 mL of chilled distilled water.
Filter the solid aspirin. Rinse the crystals and test tube with the chilled
water. Place filter with product in a watch glass to dry. Weigh and measure the melting point range
twice.
Procedure
Above: Filtering the aspirin crystals using a Buchner funnel and aspirator.
Below: The crude aspirin. This sample weighs 2.96 g.
Procedures
Recrystallizing the Crude Aspirin Dissolve crude aspirin in 10 mL of 95% ethyl
alcohol. Warm the mixture in a hot water bath. When all the aspirin has dissolved, pour in 10 mL
of lukewarm distilled water. Cover the beaker with a watch glass and set
aside to cool slowly undisturbed overnight. Collect crystals using vacuum filtering. Rinse collected crystals with cold distilled water. Allow the crystals to dry using vacuum filtering. Weigh the sample and calculate the percentage
yield out of a maximum yield of 3.9g again.
Procedure Left: Dissolving the
crude aspirin. Below: Filtering the
purified aspirin.
Procedures
Finding the Melting Point Range Place about 5 mm of aspirin crystals into a
capillary tube, which is then placed into the melttemp apparatus.
Insert a mercury thermometer through the top. Heat the apparatus until 15˚C from the expected
melting point (135˚C) at which temperature the heat should be reduced.
Record the range of the melting point as the temperature at which the first drop of liquid appears up to when all the aspirin has been converted into a liquid.
Repeat the process.
Procedure The melttemp
apparatus (left) and a view through it (below).
Final Product
Safety Safety Goggles Chemical (Acid)
Fumes Hot Plate
Don’t leave unattended
Observation
Mass of Aspirin Synthesized
Mass of Watch Glass and Filter Paper (g)
Mass of Watch Glass, Filter Paper, and Product (g)
Mass of Product (g)Crude Product
Crude Product
48.572 45.612 2.964
Final Product 48.561 51.231 2.670
Observation
Trial First Appearance of Liquid (˚C)
Completely Melted (˚C)
Crude 1 119 124
Crude 2 116 122
Crude Average
117.5 123
Trial First Appearance of Liquid (˚C)
Completely Melted (˚C)
Final 1 129 137
Final 2 130 138
Final Average
129.5 137.5
Theoretical Melting Range : 134 ~ 136
EquationsThe balanced equation is
C4H6O3 + C7H6O3 → C9H8O4 + C2H4O2
Word Equation Acetic Anhydride + Salicylic Acid = Aspirin + Acetic Acid
CalculationsMoles of a molecule = (Mass of
substance)/(Molar mass) Acetic Anhydride (C4H6O3): 102.09 g/mol
6 g / 102.09 g/mol = 0.05877 moles
Salicylic Acid (C7H6O3): 138.12 g/mol 3 g / 138.12 g/mol = 0.02172 moles
Aspirin (C9H8O4): 180.16 g/mol
Acetic Acid (C2H4O2): 60.05 g/mol
Calculations Salicylic acid is the limiting reagent
Only 0.02172 moles of aspirin will be produced.
Mass of a substance = (Moles of a substance) * (Molar mass)
180.16 g/mol x 0.02172 mol = 3.913g aspirin
CalculationsCrude Product
Maximum yield = 3.913 gActual yield = 2.96 gPercentage yield = 75.65%
Final ProductMaximum yield = 3.913 gActual yield = 2.67 gPercentage yield = 68.23%
Melting Range Percentage ErrorCrude Product
Average of actual melting range = 120.25°CExpected melting point = 135°CPercentage error = |135 - 120.25| / 135 = 0.1093 = 10.93%
Final ProductAverage of actual melting range = 133.5°CExpected melting point = 135°CPercentage error = |135 - 133.5| / 135 = 0.0111 = 1.11%
Conclusion and Analysis Pure aspirin obtained after filtering Check purity its melting point.
Impurities will always lower the melting point Aspirin= Theoretical melting range of 134-
136°C. Final product = 129.5-137.5°C. Large rigid crystal structure Low percentage error
Final product was 1.11%.
Success in synthesizing aspirin
Suggested Modifications to Procedure Temperature rise at a rate of 1-2°C per
minute Humidity kept minimum
Acetic Anhydride, Aspirin decomposes Phosphoric acid used instead of sulfuric acid
For higher yield Slower process
Sources of Experimental Error Thermometer inaccurately measured the
melting range Sensitive digital scale Impurities in the reactants or final product Contaminated lab equipments Sulfuric acid used instead of phosphoric acid
Lower yield
End of Presentation
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