Acetyl Salicylic Acid Synthesis
CIBA HS Institute
The Main IngredientSalicylic acid
H
O
Lp
Lp
O
H
Lp
O
Lp
H
An inspection of the
structural formula
of salicylic acid
shows that the
molecule consists
of the following
three units:
1. Phenol Group
H
H
H
• Benzene Ring and
Hydroxyl group
2. Carboxylic Acid
group
The Reaction
O
H
Lp
H
H
O
O
Lp
H
H
+
Lp
O
H
Lp
H
O
H
O
H
H
H
Salicylic Acid
H
Acetic
Anhydride
Side Reactions & By-Products
O
O
HO C
OH
O
HO C
OH
– H2O
O
HO C
HO C
– H2O
O
O
C
O
OH
OH
C
O
O
polyester polymer represented as
HO C
OH
– H2O
– H2O
O
O
HO C
O
C
O
O
C
OH
O
C
O
n
O
••
••
••
••
O
O O
••
CH3C-O-CCH3
C-OH
H
O

OH
••
O
••
O
C-OH
••
••
O
O
••
••
••
••
O
••
HO-CCH3
••
CCH3
••
H
••
••
H
O
••
••
••
••
••
O O
••
CH3C-O-CCH3
C-OH
H
CH3C-O-CCH3

H
••
CH3C-O-CCH3
••
C-OH
H
O
O
O
••
OH
••
••
CH3C-O-CCH3
 ••
••
H
O
C-OH
••
••
••
••
O
••
••
O
O
••
CH3C-O-CCH3
 ••
CH3C-O-CCH3
H
O
O
••
••
••
••
H
H
••
••
••
••
+
••
••
CH3C-O-CCH3
H
H
O O
••
••
••
••
O
••
••
O
••
••
••
••
••
Mechanism
O
O
C-OH
CCH3
••
O
••
Heat (exothermic)
O
C-O-H
O C-CH3
O
The Product + Heat ( exothermic)
H
Lp
O
Lp
O
Lp
Lp
O
H
H
H
O
H
+
H
H
H
O
H
O
H
H
Acetyl Salicylic Acid
Acetic Acid
H
Procedure
1. Place 1.0 g of salicylic
acid and 2.5 ml of acetic
anhydride in a small
reaction vial. Weigh the
salicylic acid as it is being
added to the vial. Add 5
drops of concentrated
Phosphoric Acid to the
vial.
2. Seal the vial with a Teflon-coated cap. Make
sure the cap is on tight. Shake the reaction
mixture.
3. Using tongs, place the sealed vial in the Vial
Heating Chamber located on the front bench set
at 85 to 95 degrees Celsius. Note the time. Note
that the reaction being used is exothermic.
4. As the reaction reaches equilibrium, temp will
have an effect on yield for the forward reaction.
4.Place 10 ml of ice and distilled water in a
50 ml beaker.
5.After 10 minutes, use tongs to remove the
vial from the Reaction Well and place on
the counter for a minute to cool. All the
solids should be dissolved before removing
the vial from the hot Reaction Well.
6. Remove the cap and pour the contents of
the reaction vial into the beaker which
contains the ice water .
7. White crystals should form shortly after the
reaction mixture is added to the ice water.
8. Rinse the reaction vial with few (1 to 2) mL
of distilled water and add it to the beaker.
Swirl the beaker with the solution.
9. Add some more ice to the mixture and let
stand for about 5-10 minutes.
Isolation Of Product
•
Place the Büchner funnel
in a filter flask (fitted with
a rubber ring) and stabilize
the assembly by clamping
the setup to a ring stand.
(See figure).
•
Weigh a piece of filter
paper and place it in a
Büchner Funnel
• Connect the suction hose to a water aspirator and
apply suction by turning on the water. Wet the filter
paper with some cold distilled water so that it
becomes well-seated over the holes in the funnel.
•
Swirl your sample a bit and pour the mixture onto the
moist filter paper in the funnel. Rinse the flask with
several small portions of ice-cold distilled water to be
sure you get as much product out as you can.
• Rinse your final product with about 15 ml of ice-cold
distilled water to remove water soluble contaminants.
• Let the product air-dry under suction for about 5
minutes.
• Carefully lift an edge of the filter paper (use a
spatula, tweezers, or stirring rod to get it
started if necessary) and remove the paper
and contents from the Büchner funnel.
Main Reaction
O
O
C-OH
OH
O
O
CH3C-O-CCH3
C-O-H
+
H
O
O C-CH3
O
acetic anhydride
salicylic acid
aspirin
CH3C-OH
Data Table
Stoichiometry
• One mole of Salicylic Acid will Produce One
Mole of Acetyl Salicylic
• 2-hydroxy Benzoic Acid (Salicylic Acid) 138.12 grams/mol
• acetate Benzoic Acid (Aspirin)- 180.17
grams/mol
Theoretical Yield
O
O
C-OH
C-O-H
O
OH
O
+
CH3C-OH
O
acetic anhydride
salicylic acid
O C-CH3
H
CH3C-O-CCH3
O
aspirin
2.0 g salicyclic acid
1 mole of aspirin
138.1 g/mole
salicyclic acid
(limiting reagent)
180.2 g aspirin
x
x
1 mole salicylic acid
=
1 mole aspirin
2.6 grams
aspirin
Mass of Salicylic Acid
Molecular Formula of Salicylic
Acid
Moles of Salicylic Used
Grams
C7H6O3
mol
Molar Mass of Salicylic Acid
g/mol
Density of Acetic Anhydride
1.080 g/ml
Volume of Acetic Anhydride Used
Mass of Acetic Acid Used
Molecular Formula of Acetic
Anhydride
Moles of Acetic Anhydride Used
2.50 ml
g
C4H6O3
mol
Limiting Reagent
Mass of Aspirin Synthesized
grams
Molecular Formula of Aspirin
C9H8O4
Molar Mass of Aspirin
Moles of Aspirin Synthesized
g/mol
mol
Theoretical Yield of Aspirin
Synthesized
g
Experimental Yield of Aspirin
g
% Yield