Preparation of Aspirin

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Preparation of Aspirin
Intro to Chemistry Chem1020 Lab

• Chemistry Department
• Minneapolis Community Technical College

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Overview

• Part I
• Introduction
• Part II
• Synthesis of aspirin
• Part III
• Separation of aspirin
• Part IV
• Testing of aspirin
• Part V
• Calculation

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Part I. Introduction

• In this experiment you will learn how to use a
  chemical reaction to make new substances such as
  aspirin
• Salicylic acid Acetic anhydride
  Aspirin Acetic acid
• You will also learn how to separate the desired
  product from other substances, which is as
  important as the synthesis itself.
• During the following week, you will evaluate the
  quantity and purity of the aspirin product.
• Stoichiometric calculation, a topic
• covered in Chapter 9.3 in the text-
• book, will be performed on this reaction.

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Part II. Preparation

• 1.5 g salicylic acid
• Use the attached spatula for transferring.
• Weigh it on a diagonally-folded and zeroed
  weighing paper.
• Record its exact mass.

• 2 mL acetic anhydride
• Use the provided graduated cylinder to measure.

• 4 drops phosphoric acid
• It serves as a catalyst, which speeds up reaction
  without changing its own composition.
• Use the provided pipette dropper.

An Erlenmeyer flask
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Part II. Precautions!

• For any chemicals, always put the cap back onto
  its container after each use, even if someone
  will be using it right after you.
• Salicylic acid is a fluffy solid. Be careful not
  to make a mess at the weighing station. In case
  of spilling, alert the instructor immediately.
• Both acetic anhydride and phosphoric acid are
  corrosive and reactive.
• Keep them inside the fume hood.
• Be careful not to get it onto your skin.
• In case of spilling, alert the instructor
  immediately.

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Part II. Preparation (Heating is done in fume
hood)

1. Clamp and tilt the Erlenmeyer flask allowing the
   solid to mix with the liquid inside the flask.

1. Lower the flask into a water-bath which sits
   above a hot plate. Insert a thermometer into the
   water-bath (not the flask) to monitor
   temperature. Turn on the heating knob (the right
   one) of the hot plate all

Setup side view
the way to high.
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Part II. Preparation

1. When the temperature reaches 80 ºC, turn off the
   hot plate.
2. Swirl the flask gently to let all solids
   dissolve. If you have to take the flask out of
   the water bath to shake, put it back as soon as
   all solids dissolve. Keep it in the water bath
   for 5 minutes.
3. Take the flask out of the water bath and let it
   cool down undisturbed (meaning no shaking or
   stirring). Eventually most of the liquid will
   crystallize, generating a white, crystalline cake
   at the bottom of the flask. That solid, should
   be mainly the aspirin product.
4. Add enough ice-cold water into the flask and use
   a glass stirring rod to break up the solid
   chunks.

.
Ice-cold distilled water
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Part III. Separation
Now the solid aspirin is mixed with other
substances unreacted reactants, phosphoric acid
catalyst, acetic acid the other product. To
separate aspirin from them, vacuum filtration
will be used.
Buchner funnel
Setup side view
Setup front view
filtration flask
electric pump
on/off switch
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Part III. Separation

1. Determine and record the total mass of a watch
   glass and a filter paper. Write your name on the
   edge of the paper.

1. Turn on the pump. Quickly swirl and pour the
   reaction mixture into the funnel. Use the
   ice-cold water to rinse out all solid in the
   flask.
2. Squirt more ice-cold water onto the crystals in
   the Buchner funnel to wash away other impurities.
3. Use a micro spatula to pick out the filter paper
   with aspirin, and put them on the watch glass for
   drying over one week.

John D.

1. Put the filter paper into the Buchner funnel.
   Wet it with ice-cold water so that it fits nicely
   in the funnel.

John D.
Ice-cold distilled water
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Part IV. Testing(Done a Week Later)

• Quantity
• Determine and record the total mass of watch
  glass, filter paper, and aspirin product
• Quality
• Determine the purity of your product
• Your instructor will demonstrate that pure
  salicylic acid (one of the reactants) and pure
  commercial aspirin show different colors when
  mixed with an FeCl3 solution.
• Use the provided semi-micro spatula to transfer a
  small amount (match-head size) of your product
  into the test tube, and add 2 drops of 1 FeCl3
  solution. Compare the resulting color to the
  instructors results. Draw a conclusion about
  the purity of your product.

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Part V. Sample Calculation

• Data
• a. Msalicylic acid 1.52 0.01 g b. Mwatch
  glass filter paper 19.18 0.01 g
• c. Mwatch glass filter paper aspirin
  20.98 0.01 g
• Calculation
• Actual yield of aspirin Mwatch glass filter
  paper aspirin - Mwatch glass filter paper
• 20.98 19.18 1.80 g (2 decimal
  places)
• b. Theoretical yield of aspirin
• Salicylic acid Acetic anhydride
  Aspirin Acetic acid
• Molecular formulas C7H6O3
  C9H8O4
• Molar masses 138.12 g/mol
  180.16 g/mol