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Complete explanation of synthesis of aspirin
Typology: Schemes and Mind Maps
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Aspirin is most widely sold over-the-counter drug. It has the ability to reduce fever (an antipyretic), to
reduce pain (an analgesic), and to reduce swelling, soreness, and redness (an anti-inflammatory agent). One of
the first recorded accounts for the discovery of aspirin appeared in England, in 1763, crediting the bark of
willow trees with a beneficial effect in alleviating distress due to fevers, aches, and pains. Later, the compound
salicylic acid (named for the Latin word for willow, salix) was isolated from willow bark. It proved to be the
active ingredient. By 1860, organic chemists were able to synthesize salicylic acid from basic starting materials,
this furthered the therapeutic use of the substance, but there were problems. Salicylic acid proved to be irritating
to the membranes of the throat, mouth, and stomach. These problems are directly associated with the high
acidity of the compound, but a simple remedy was discovered, namely, replacement of the acidic phenolic
hydrogen atom with an acetyl group.
When interpreting the structures of the above organic compounds, note the following characteristics of these
molecules. Organic molecules are complex compounds of carbon. Carbon always shares four pairs of electrons
in bonds with other molecular groups or atoms. When the structure of an organic molecule is drawn using the
condensed method, carbon rings are represented with simple geometric shapes, such as a hexagon. Each corner
of the hexagon represents a carbon atom and the number of hydrogen atoms required to share 4 pairs of
electrons with the carbon. If the “corner” has no other marks, that means there is a carbon atom bonded to 2
other carbon atoms (in the ring) plus 2 hydrogen atoms. The hydrogen atoms are implied, not show. If a carbon
to carbon double bond (C =C) is present and the carbons are attached in a ring, each of the two carbon atoms is
bonded to two others with 6 pairs of electrons, and only one hydrogen is attached to each of these carbons give
the full compliment of four bonds. If a triple bond is present then only one other atom may be attached. Check
the structures below to see that each carbon has four and only four bonds. Oxygen, on the other hand, will bond
covalently to only two atoms, and hydrogen bonds to only one.
A useful synthesis of acetylsalicylic acid was developed in 1893, patented in 1899, marketed under the trade
name of “aspirin” by the Bayer Company in Germany. The name aspirin was invented by the chemist, Felix
Hofmann, who originally synthesized acetylsalicylic acid for Bayer. More than 50 million 5-grain tablets of
aspirin are consumed daily in the United States. In Part I of this experiment, you will prepare aspirin by reaction
of salicylic acid with acetic anhydride, using concentrated sulfuric acid as a catalyst.
Aspirin still has its side effects. Note that the carboxylic acid functional group remains intact.
This may result in hemorrhaging of the stomach walls even with normal dosages. The acidic irritation can
be reduced through the use of buffering agents, like antacids, in the form of magnesium hydroxide, magnesium
carbonate, and aluminum glycinate when mixed with aspirin (Bufferin). While the ester can be formed from
acetic acid and salicylic acid, a better preparative method uses acetic anhydrides in the reaction instead of acetic
acid. An acid catalyst, like sulfuric acid or phosphoric acid, is used to speed up the process.
Part I: Synthesis of Aspirin
Caution! The preparation of aspirin involves the use of two very hazardous materials - concentrated sulfuric
acid and acetic anhydride. Proceed only if you have a fume hood to work in, and after you have listened
carefully to the instructor’s safety directions. As usual, goggles must be worn at all times.
to calculate the theoretical yield of aspirin. Record the weigh on the report sheet.
the skin and eyes.)
flask in a beaker of boiling water. Clamp the flask to a ring stand and heat for 20 minutes. Constantly stir
with a glass rod; the entire solid must completely dissolve.
occur during cooling. If crystals begin to grow, let the flask sit undisturbed until crystals stop growing then
add the 40 mL of ice water. If crystals do not grow, slowly pour the solution into a 250-mL beaker
containing 40 mL of ice water, mix thoroughly, and place the beaker in ice water and let sit undisturbed
until crystals have grown. The water destroys any unreacted acetic anhydride and will cause the insoluble
aspirin to precipitate out of solution.
Allow the crude product to dry, then weigh it on the rough balance.
the paper so that a few crystals of aspirin enter the capillary tube.
bottom. The aspirin crystals should be firmly packed, and fill the capillary tube to a depth of no more than
1 - 2 mm. Insert the capillary tube containing the sample into the melting point apparatus. Record the
temperature where the melting point is first observed and when it becomes a liquid completely. This is your
melting point range. Melting point of purified aspirin is 135-136 °C.
B. Determination of Purity
Phenols form a colored complex with the ferric ion. If phenol is present in a sample, the resulting color means
the product is impure. The purple color indicates the presence of a phenol group. The intensity of the color
qualitatively tells how much impurity is present.
into test tube #2, and a small sample of crushed commercial aspirin into #3. Add 5 mL of deionized water to
each test tube and swirl to dissolve the crystals.
Scientist
Partner(s)
REPORT SHEET
Part I
g salicylic acid ( 138 gsalicylicacid
1 molsalicylic acid )( 1 molaspirin
1 molsalicylic acid )( 1 molaspirin
180 g aspirin ) = g of aspirin
(Theoretical yield of aspirin)
Weight of aspirin & watch glass g
Weight of watch glass g
Mass of crude product obtained after suction filtration g
Percent Yield of crude product ( theoreticalyield
experimental yield 100%) %
Mass of re-crystallized product (optional) g
Percent Yield of re-crystallized product ( theoreticalyield
experimental yield 100%) %
Part II
Melting Point of crude product (1st trial) °C (2nd trial) °C
Melting Point of re-crystallized product (1st trial) °C (2nd trial) °C
Ferric Chloride Test (Purity test)
Salicylic acid
Your aspirin
Commercial aspirin