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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