Aspirin synthesis for AS/A2 Level chemistry.
Chemistry Department
Outreach Team.
Charlie Archer, The Oratory School, Reading, 2008
Aspirin is one of the most commonly used drugs in the world, so why not bring chemistry out of the text books, and synthesise aspirin in the
undergraduate chemistry laboratory at Reading University. Using familiar A' level chemistry, you will produce aspirin using an esterification reaction
with ethanoic anhydride. The starting material, for this synthesis, is 2-Hydroxybenzoic acid (salicylic acid)., Salicylic acid is the naturally occurring
analgesic, that can be extracted from willow bark, but is very bitter and less effective than aspirin.
O
OH
O
H 3C
O
OH
+
[H ]
O
O
H 3C
+
O
O
O
cat
OH
Reflux
+
H3C
OH
H 3C
2-hydroxybenzoic acid
salicylic acid
The reaction
The aspirin is formed when you reflux
ethanoic anhydride, phosphoric acid,
and 2-hydroxybenzoic acid together for
15 minutes. Quenching the reaction
mixture with cold water forces the crude
aspirin out of solution. This crude aspirin
can then be isolated by filtration.
aspirin
2-(acetyloxy)benzoic acid
Re-crystallisation
The crude aspirin obtained, is
purified by re-crystallisation from
a minimum volume of hot
aqueous ethanol. The pure aspirin
crystals formed are separated and
dried by vacuum filtration
ethanoic anhydride
2-(acetyloxy)benzoic acid
acetic anhydride
Testing the product
The purity of your aspirin sample
can then be assessed by using
both: thin layer chromatography
(TLC), with visualisation by U.V.
and determination of its melting
point.
What the students thought about the aspirin synthesis:
“Very interesting and fun to do”
“We used different types of equipment not available at school”
“It showed the usefulness of chemistry in real-life
situations”
aspirin
ethanoic acid
acetic acid
The pure aspirin
At the end, the
teacher may be
on their knees,
but they’re
still smiling.