2. Introduction :
• Salicylic acid which is a constituent of certain plant is
itself an analgesic & was originally administered as
sodium salicylate, since salicylic acid has an irritating
effect on the stomach, chemists thought of a modification
which would retain its properties while decreasing the
adverse side effects.
• Conversion to the ester satisfied this requirement&
aspirin proved to be as effective as sodium salicylate
without the irritation of phenolic compound.
• Aspirin however hydrolyzed to salicylic acid in the
alkaline media of the intestine by esterase enzyme.
3. history
The aspirin we know came into being in the late
1890s in the form of acetylsalicylic acid when
chemist Felix Hoffmann at Bayer in Germany used
it to alleviate his father's rheumatism, a timeline
from Bayer says. Beginning in 1899, Bayer
distributed a powder with this ingredient to
physicians to give to patients.The drug became a
hit and, in 1915, it was sold as
over-the-counter tablets.
4. An ester is a chemical compound derived from an acid (organic or inorganic) in
which at least one –OH hydroxyl group is replaced by an –O– alkyl (alkoxy)
group, as in the substitution reaction of a carboxylic acid and an alcohol.
Salicylic acid contains a phenol group, and phenols are
known to be irritating. because replaced the phenol group
with an ester group.
When phenol group replace to ester group, that salicylic acid
change to acetylsalicylic acid, was much less irritating than salicylic acid.
Unfortunately, it is still irritating to the stomach and can cause hemorrhaging of
the stomach walls.
ESTRER AND EFFECT IN SYNTHESIS OF ASPIRIN
6. Synthesis of aspirin
• Aspirin is prepared in our lab by acetylating of
salicylic acid with acetic anhydride in the presence
of H2SO4 as catalyst.
7. • Because of its low solubility in H2O it is isolated from the
reaction mixture by precipitation with H2O, we pour cold water
to hydrolyze acetic anhydride & complete the ppt of aspirin.
• Heat is produced in this reaction (exothermic reaction)
• Aspirin recrystallized from benzene, even though aspirin is
insoluble in cold water & soluble in hot water but it is not a
suitable recrystallizing solvent for Aspirin because aspirin
undergoes partial hydrolysis to salicylic acid & acetic acid in
hot water.
8. Procedure:
1-Place 3 gm of salicylic acid in 100 ml E.f. and add with
constant stirring 6 ml of acetic anhydride followed by 1 ml of
conc. H2SO
2- Stir the mixture gently observing the rise in temp. to 70-80 oC.
While the salicylic acid dissolves, after 15 minutes the solution
cools by it self and a solid mass of aspirin forms
3-Pour 35 ml of ice-cold water over the contents of the flask to
hydrolyze excess acetic anhydride and to complete the ppt of
aspirin
4- Collect the crude aspirin using a Buchner funnel and wash
with ice-cold water, air-dry the product and calculate the yield
5- Perform FeCl3 test on produced aspirin
9. Identification test of
aspirin:
• Ferric chloride test;
• The presence of phenolic group in a compound is
indicated by the formation of violet iron complex
when treated with ferric chloride solution
• Aspirin ------------► give –ve result with FeCl3 due to
absence of phenolic group
• Salicylic acid--------► + ve result
11. Think
• What is le chatelier’s principle?
• Mention methods in formulation or synthesis to overcome
the problem of irritability of salicylic acid to stomach?
• Why cold water is used in Aspirin washing?
• What are the methods which are used to assesse aspirin
purity?
• List the steps used for recrystallization.
• What is the difference between vacuum filtration &
gravity filtration?
