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EXERCISE 11
SYNTHESIS OF ASPIRIN
(ACETYLSALICYLIC ACID FROM SALICYLIC ACID)

JAN PAULA BOTE
GROUP 3
17L

I. Introduction

Aspirin is a well-known therapeutic drug that was first synthesized in a pure and stable form by Felix Hoffman in 1897 (Beran, 2011). It is known as an anti-platelet drug during the early 70s. For secondary prophylaxis of vascular disease, it is the most useful and cost-effective drug (Quinn, 2008). “Pure aspirin, chemically called as acetylsalicylic acid, is both an organic ester and an organic acid.” It is considered as an analgesic. This effect is due to the salicylate ion (Beran, 2011). Salicylic acid is one of the oldest pain reliever used from chewing willow leaves to reduce fever and inflammation during the time of Hippocrates and other Greek physicians (Eaton, 1980). Salicylic acid causes severe stomach problems than aspirin so aspirin is more commonly used today (Beran, 2011). “Aspirin (molar mass of 180.2 g/mol) is prepared by reacting salicylic acid with acetic anhydride. Aspirin, like many other organic compounds is a weak monoprotic acid (Beran, 2011).”

Figure 11.1 Synthesis Reaction of Aspirin

Aspirin is prepared via acid-catalyzed acetylation or nucleophilic acyl substitution of salicylic acid by acetic anhydride (Moore & Wilson, 1996). A nucleophilic acyl substitution is initiated by the addition of the leaving group bonded to the carbonyl carbon by an attacking nucleophile (McMurry & Begley, 2005).

II. Objectives

1. To explain the concept of organic synthesis;
2. To synthesize acetylsalicylic acid from salicylic acid by nucleophilic acyl substitution; and 3. To describe and explain differences in the properties of acetylsalicylic acid and salicylic acid by simple chemical tests. III. Materials and Methods

A. Schematic Diagram of the Procedure

Preparation of Acetylsalicylic Acid (Aspirin)

Crude Aspirin
Crude Aspirin
- wash crystals with cold H2O (several times)
- transfer to pre-weighed watch glass
- air dry
- weigh dried asprin
- calculate percent yield
- wash crystals with cold H2O (several times)
- transfer to pre-weighed watch glass
- air dry
- weigh dried asprin
- calculate percent yield
Discard
Discard
Asprin crystals
Asprin crystals
Filtrate
Filtrate
+ 3 ml acetic anhydride
+ 5 drops 85% phosphoric acid
- swirl to mix
in steam bath for 15 mins
+ 2 ml dH2O slowly
+ 20 ml ice-cold H2O (when vigorous rxn ended)
- cool to RT
- place in an ice bath
- suction filtration

+ 3 ml acetic anhydride
+ 5 drops 85% phosphoric acid
- swirl to mix
in steam bath for 15 mins
+ 2 ml dH2O slowly
+ 20 ml ice-cold H2O (when vigorous rxn ended)
- cool to RT
- place in an ice bath
- suction filtration

1 g salicylic acid
(125 ml E. flask)
1 g salicylic acid
(125 ml E. flask)

Melting point determination
Melting point determination
Recrystallization of aspirin
Recrystallization of aspirin
end
end
end
end
- 5 drops dH2O
- 5 drops iodine sol’n
- observe
- 5 drops dH2O
- 5 drops iodine sol’n
- observe
- 5 drops dH2O
- 5 drops iodine sol’n
- observe
- 5 drops dH2O
- 5 drops iodine sol’n
- observe
Commercial aspirin
Commercial aspirin
Synthesized aspirin
Synthesized aspirin
end
end
- determine melting point of crude and recrystallized aspirin (w/ melting point determination apparatus) - compare
- account for difference
- determine melting point of crude and recrystallized aspirin (w/ melting point determination apparatus) - compare
- account for difference
Recrystallized Aspirin
Recrystallized Aspirin
- transfer to watch glass
- air dry
- weigh
- calculate % recovery
- transfer to clean vial
- transfer to watch glass
- air dry
- weigh
- calculate % recovery
- transfer to clean vial
Aspirin crystals
Aspirin crystals
Discard
Discard
Filtrate
Filtrate
- transfer to 125 ml E. flask
- add water dropwise while swirling until almost all crude aspirin...
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