Transcript Week #11: Synthesis of Aspirin and Oil of Wintergreen

CH 104: SYNTHESIS OF ASPIRIN AND
OIL OF WINTERGREEN
• Is it animal, vegetable, or
mineral?
• Until the mid-1800s most
scientists thought that all
carbon compounds
originated from plants and
animals.
• As a result, organic
chemistry was defined as
the chemistry of carbon.
• In contrast, inorganic
chemistry was defined as
the chemistry of minerals.
ORGANIC CHEMISTRY AND FUNCTIONAL GROUPS
• Today’s experiment is an example of organic chemistry.
• Organic molecules usually have very complicated
structures. Therefore, organic chemists often use specific
parts of molecules when they make other compounds.
These parts are called functional groups.
• A functional group is an atom or group of atoms that
defines the structure, physical properties, and chemical
reactivity of a particular family of organic compounds.
• In today’s experiment you will use different functional
groups to synthesize aspirin (acetylsalicylic acid) from
salicylic acid and acetic anhydride, and oil of wintergreen
(methyl salicylate) from salicylic acid and methanol.
THE SYNTHESIS OF ASPIRIN
• This is an esterification reaction. A phenol (the
functional group
of salicylic acid) reacts with an acid anhydride (the
functional group of acetic anhydride) to make an ester (the
functional group of acetylsalicylic acid).
THE SYNTHESIS OF ASPIRIN
• What happens to acetic anhydride?
• It’s cut in 2. One piece is bonded to salicylic acid. The other piece
helps make acetic acid.
• What happens to the phenolic H from salicylic acid?
• It goes from salicylic acid to the acetic acid.
• Which is more likely? This reaction happens in 1 step or more than 1
step?
• This is a complicated reaction. It probably has more than 1 step.
• A reaction mechanism is a
detailed account of every
valence electron during a
reaction.
• The reaction mechanism for
the catalytic esterification
of salicylic acid and acetic
anhydride has 5 steps.
• Use Lewis structures to
predict the product of each
step.
• What is the catalyst?
• H+. It is recycled during the
reaction. It is not
permanently created. And
it is not permanently
consumed.
THE SYNTHESIS OF ASPIRIN
• Your aspirin will most likely be contaminated with salicylic acid. It
should NOT be ingested.
• Iron(III) chloride (FeCl3) will be used to detect unreacted salicylic acid.
• The Fe3+ from FeCl3 usually reacts with phenol (
) to make a
highly colored complex ion. Salicylic acid has a phenol group;
therefore, it gives a positive (purple) test with FeCl3. Acetylsalicylic
acid does NOT have a phenol group; therefore, it gives a negative (no
color change) test with FeCl3.
THE SYNTHESIS OF OIL OF WINTERGREEN
• In the last esterification reaction the phenolic group (
) of
salicylic acid was attacked. In this esterification reaction the
carboxylic acid group (
) from salicylic acid is attacked. It reacts
with an alcohol (
) to make a different ester (
), oil of
wintergreen (methyl salicylate).
• What is the difference between a phenol and an alcohol?
• A phenol has OH bonded to an aromatic ring (Ar). An alcohol has OH
bonded to an aliphatic chain (R).
THE SYNTHESIS OF OIL OF WINTERGREEN
• What happens to methanol?
• It’s cut in 2. One piece is bonded to salicylic acid. The other piece
helps make water.
• What happens to the alcoholic H from methanol?
• It goes from methanol to the water.
• Which is more likely? This reaction happens in 1 step or more than 1
step?
• Again, this is a complicated reaction. It probably has more than 1 step.
• The reaction mechanism for
the catalytic esterification
of salicylic acid and
methanol has 5 steps.
• Use Lewis structures to
predict the product of each
step.
• What is the catalyst?
• H+. It is recycled during the
reaction. It is not
permanently created. And
it is not permanently
consumed.
SAFETY
• Give at least 1 safety concern for the following procedures that will be
used in today’s experiment.
• Heating glass with a hot plate or a flame.
• Injury from a burn or causing a fire. Be careful. Do not wear loose
clothing or long hair. Glass can shatter when heating; wear your
goggles at all times.
• Using salicylic acid, acetic anhydride, concentrated H2SO4, 1% FeCl3,
and methyl alcohol.
• These are irritants. Wear your goggles at all times. Immediately clean
all spills. If you do get either of these in your eye, immediately flush
with water.
• Generating H2O(g) and acidic gases.
• Again, these are irritants. Wear your goggles at all times. Use the
fume hood when handing concentrated H2SO4. Immediately clean all
spills. If you do get either of these in your eye, immediately flush with
water.
• Your laboratory manual has an extensive list of safety procedures.
Read and understand this section.
• Ask your instructor if you ever have any questions about safety.
SOURCES
• The Chemical Heritage Foundation. 2002. Making Aspirin –
Teacher’s Guide.
http://www.chemheritage.org/educationalservices/pharm/tg
/antibiot/activity/asp31.htm Available: [accessed 18
January 2007].
• Morrison, RT, RN Boyd. 1983. Organic Chemistry, 4th ed.
Boston, MA: Allyn and Bacon, Inc.
• Pavia, DL, GM Lampman, GS Kriz. Introduction to Organic
Laboratory Techniques, 2nd ed. New York, NY: Saunders
College Publishing.
• Joseph Wright of Derby. 1771. The Discovery of
Phosphorus.